| 51. |
- Illergård, Kristoffer, et al.
(author)
-
Structure is three to ten times more conserved than sequence-A study of structural response in protein cores
- 2009
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 77:3, s. 499-508
-
Journal article (peer-reviewed)abstract
- Protein structures change during evolution in response to mutations. Here, we analyze the mapping between sequence and structure in a set of structurally aligned protein domains. To avoid artifacts, we restricted our attention only to the core components of these structures. We found that on average, using different measures of structural change, protein cores evolve linearly with evolutionary distance (amino acid substitutions per site). This is true irrespective of which measure of structural change we used, whether RMSD or discrete structural descriptors for secondary structure, accessibility, or contacts. This linear response allows us to quantify the claim that structure is more conserved than sequence. Using structural alphabets of similar cardinality to the sequence alphabet, structural cores evolve three to ten times slower than sequences. Although we observed an average linear response, we found a wide variance. Different domain families varied fivefold in structural response to evolution. An attempt to categorically analyze this variance among subgroups by structural and functional category revealed only one statistically significant trend. This trend can be explained by the fact that beta-sheets change faster than alpha-helices, most likely due to that they are shorter and that change occurs at the ends of the secondary structure elements. Proteins 2009; 77:499-508. (C) 2009 Wiley-Liss, Inc.
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| 52. |
- Illergård, Kristoffer, et al.
(author)
-
Why are polar residues within the membrane core evolutionary conserved?
- 2011
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 79:1, s. 79-91
-
Journal article (peer-reviewed)abstract
- Here, we present a study of polar residues within the membrane core of alpha-helical membrane proteins. As expected, polar residues are less frequent in the membrane than expected. Further, most of these residues are buried within the interior of the protein and are only rarely exposed to lipids. However, the polar groups often border internal water filled cavities, even if the rest of the sidechain is buried. A survey of their functional roles in known structures showed that the polar residues are often directly involved in binding of small compounds, especially in channels and transporters, but other functions including proton transfer, catalysis, and selectivity have also been attributed to these proteins. Among the polar residues histidines often interact with prosthetic groups in photosynthetic-and oxidoreductase-related proteins, whereas pro-lines often are required for conformational changes of the proteins. Indeed, the polar residues in the membrane core are more conserved than other residues in the core, as well as more conserved than polar residues outside the membrane. The reason is twofold; they are often (i) buried in the interior of the protein and (ii) directly involved in the function of the proteins. Finally, a method to identify which polar residues are present within the membrane core directly from protein sequences was developed. Applying the method to the set of all human membrane proteins the prediction indicates that polar residues were most frequent among active transporter proteins and GPCRs, whereas infrequent in families with few transmembrane regions, such as non-GPCR receptors. Proteins 2011; 79: 79-91.
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| 53. |
- Irbäck, Anders, et al.
(author)
-
Folding thermodynamics of three beta-sheet peptides: A model study
- 2004
-
In: Proteins. - : Wiley. - 0887-3585. ; 56:1, s. 110-116
-
Journal article (peer-reviewed)abstract
- We study the folding thermodynamics of a beta-hairpin and two three-stranded beta-sheet peptides using a simplified sequence-based all-atom model, in which folding is driven mainly by backbone hydrogen bonding and effective hydrophobic attraction. The native populations obtained for these three sequences are in good. agreement with experimental data. We also show that the apparent native population depends on which observable is studied; the hydrophobicity energy and the number of native hydrogen bonds give different results. The magnitude of this dependence matches well with the results obtained in two different experiments on the beta-hairpin. (C) 2004 Wiley-Liss, Inc.
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| 54. |
- Irbäck, Anders, et al.
(author)
-
Spontaneous beta-barrel formation: an all-atom study of Abeta(16-22) oligomerization
- 2008
-
In: Proteins. - : Wiley. - 0887-3585. ; 71:1, s. 207-214
-
Journal article (peer-reviewed)abstract
- Using all-atom Monte Carlo simulations with implicit water, combined with a cluster size analysis, we study the aggregation of A16-22, a peptide capable of forming amyloid fibrils. We consider a system of six initially randomly oriented A16-22 peptides, and investigate the thermodynamics and structural properties of aggregates formed by this system. The system is unaggregated without ordered secondary structure at high temperature, and forms -sheet rich aggregates at low temperature. At the crossover between these two regimes, we find that clusters of all sizes occur, whereas the -strand content is low. In one of several runs, we observe the spontaneous formation of a -barrel with six antiparallel strands. The -barrel stands out as the by far most long-lived aggregate seen in our simulations.
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| 55. |
- Irbäck, Anders, et al.
(author)
-
Thermal versus mechanical unfolding of ubiquitin
- 2006
-
In: Proteins. - : Wiley. - 0887-3585. ; 65:3, s. 759-766
-
Journal article (peer-reviewed)abstract
- The authors studied the temperature-induced unfolding of ubiquitin by all-atom Monte Carlo simulations. The unfolding behavior is compared with that seen in previous simulations of the mechanical unfolding of this protein, based on the same model. In mechanical unfolding, secondary-structure elements were found to break in a quite well-defined order. In thermal unfolding, the authors saw somewhat larger event-to-event fluctuations, but the unfolding pathway, was still far from random. Two long-lived secondary-structure elements could be identified in the simulations. These two elements have been found experimentally to be the thermally most stable ones. Interestingly, one of these long-lived elements, the first P-hairpin, was found to break early in the mechanical unfolding simulations. Their combined simulation results thus enable the authors to predict in detail important differences between the thermal and mechanical unfolding behaviors of ubiquitin.
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| 56. |
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| 57. |
- Janowski, R, et al.
(author)
-
3D domain-swapped human cystatin c with amyloidlike intermolecular beta-sheets
- 2005
-
In: Proteins. - : Wiley. - 0887-3585. ; 61:3, s. 570-578
-
Journal article (peer-reviewed)abstract
- Oligomerization of human cystatin C (HCC) leads to amyloid deposits in brain arteries, and this process is greatly accelerated with a naturally occurring L68Q variant. The crystal structures of N-truncated and full-length HCC (cubic form) showed dimer formation via three-dimensional (3D) domain swapping, and this observation has led to the suggestion that an analogous domain-swapping mechanism, but propagated in an open-ended fashion, could be the basis of HCC fibril formation. Here we report that full-length HCC, when crystallized in a new, tetragonal form, dimerizes by swapping the same secondary structure elements but with a very different overall structure generated by the flexibility of the hinge linking the moveable elements. The beta-strands of the beta-cores of the two folding units of the present dimer are roughly parallel, while they formed an angle of about 100 degrees in the previous two structures. The dimers pack around a crystallographic dyad by extending their molecular beta-sheets in an intermolecular context. At the other edge of the molecular beta-sheet, side-chain-side-chain hydrogen bonds propagate the beta-structure in the same direction. In consequence, a supramolecular crystal structure is generated, with all the P-strands of the domain-swapped dimers being perpendicular to one crystallographic direction. This observation is relevant to amyloid aggregation of HCC, as X-ray diffraction studies of amyloid fibrils show them to have ordered, repeating structure, consistent with the so-called cross-beta structure, in which extended polypeptide chains are perpendicular to the fiber axis and form infinite beta-sheets that are parallel to this axis.
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| 58. |
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| 59. |
- Jones, TA, et al.
(author)
-
CASP3 comparative modeling evaluation
- 1999
-
In: Proteins. - 0887-3585 .- 1097-0134. ; , s. 30-46
-
Journal article (peer-reviewed)abstract
- We report our evaluation of the CASP3 comparative modelling competition. Our analysis covers the accuracy of the over-all fold, the bridging of insertions and deletions, and the adding of side-chains. We describe our attempts at automating aspects of the evaluation.
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| 60. |
- Jonsson, Sigurdur, et al.
(author)
-
Distinct phases of free α-synuclein - A Monte Carlo study.
- 2012
-
In: Proteins. - : Wiley. - 0887-3585. ; 80:9, s. 2169-2177
-
Journal article (peer-reviewed)abstract
- The α-synuclein protein (αS), implicated in Parkinson's disease (PD), shows conformational versatility. It aggregates into β-sheet-rich fibrils, occurs in helical membrane-bound forms, is disordered as a free monomer, and has recently been suggested to have a folded helical tetramer as its main physiological form. Here we use implicit solvent all-atom Monte Carlo (MC) methods to explore the conformational ensemble sampled by the free αS monomer. We analyze secondary-structure propensities, size and topological properties, and compare with existing experimental data. Our study suggests that free αS has two distinct phases. One phase has the expected disordered character. The other phase also shows large conformational variability. However, in this phase, the β-strand content is substantial, and the backbone fold shows statistical similarities with that in αS fibrils. Presence of this phase is consistent with data from low-temperature experiments. Conversion of disordered αS to this fibril-like form requires the crossing of a rather large apparent free-energy barrier. Proteins 2012. © 2012 Wiley Periodicals, Inc.
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| 61. |
- Julenius, Karin, et al.
(author)
-
Coupling of ligand binding and dimerization of helix-loop-helix peptides: Spectroscopic and sedimentation analyses of calbindin D-9k EF-hands
- 2002
-
In: Proteins. - : Wiley. - 0887-3585. ; 47:3, s. 323-333
-
Journal article (peer-reviewed)abstract
- Isolated Ca2+-binding EF-hand peptides have a tendency to dimerize. This study is an attempt to account for the coupled equilibria of Ca2+-binding and peptide association for two EF-hands with strikingly different loop sequence and net charge. We have studied each of the two separate EF-hand fragments from calbindin D-9k. A series of Ca2+-titrations at different peptide concentrations were monitored by CD and fluorescence spectroscopy. All data were fitted simultaneously to both a complete model of all possible equilibrium intermediates and a reduced model not including dimerization in the absence of Ca2+. Analytical ultracentrifugation shows that the peptides may occur as monomers or dimers depending on the solution conditions. Our results show strikingly different behavior for the two EF-hands. The fragment containing the N-terminal EF-hand shows a strong tendency to dimerize in the Ca2+-bound state. The average Ca2+-affinity is 3.5 orders of magnitude lower than for the intact protein. We observe a large apparent cooperativity of Ca2+ binding for the overall process from Ca2+-free monomer to fully loaded dimer, showing that a Ca2+-free EF-hand folds upon dimerization to a Ca2+-bound EF-hand, thereby presenting a preformed binding site to the second Ca2+-ion. The C-terminal EF-hand shows a much smaller tendency to dimerize, which may be related to its larger net negative charge. In spite of the differences in dimerization behavior, the Ca2+ affinities of both EF-hand fragments are similar and in the range IgK = 4.6-5.3.
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| 62. |
- Karlsson, B Göran, 1962, et al.
(author)
-
Solution structure of the calmodulin-like C-terminal domain of Entamoeba-actinin2
- 2016
-
In: Proteins-Structure Function and Bioinformatics. - : Wiley. - 0887-3585 .- 1097-0134. ; 84:4, s. 461-466
-
Journal article (peer-reviewed)abstract
- Cell motility is dependent on a dynamic meshwork of actin filaments that is remodelled continuously. A large number of associated proteins that are severs, cross-links, or caps the filament ends have been identified and the actin cross-linker -actinin has been implied in several important cellular processes. In Entamoeba histolytica, the etiological agent of human amoebiasis, -actinin is believed to be required for infection. To better understand the role of -actinin in the infectious process we have determined the solution structure of the C-terminal calmodulin-like domain using NMR. The final structure ensemble of the apo form shows two lobes, that both resemble other pairs of calcium-binding EF-hand motifs, connected with a mobile linker. Proteins 2016; 84:461-466.
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| 63. |
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| 64. |
- Knapp, S, et al.
(author)
-
Thermal unfolding of small proteins with SH3 domain folding pattern
- 1998
-
In: Proteins. - 0887-3585 .- 1097-0134. ; 31:3, s. 309-319
-
Journal article (peer-reviewed)abstract
- The thermal unfolding of three SH3 domains of the Tec family of tyrosine kinases was studied by differential scanning calorimetry and CD spectroscopy, The unfolding transition of the three protein domains in the acidic pH region can be described as a reversible two-state process. For all three SH3 domains maximum stability was observed in the pH region 4.5 < pH < 7.0 where these domains unfold at temperatures of 353K (Btk), 342K (Itk), and 344K (Tec), At these temperatures an enthalpy change of 196 kJ/mol, 178 kJ/mol, and 169 kJ/mol was measured for Btk-, Itk-, and Tec-SH3 domains, respectively. The determined changes in heat capacity between the native and the denatured state are in an usual range expected for small proteins. Our analysis revealed that all SH3 domains studied are only weakly stabilized and have free energies of unfolding which do not exceed 12-16 kJ/mol but show quite high melting temperatures. Comparing unfolding free energies measured for eukaryotic SH3 domains with those of the topologically identical Sso7d protein from the hyperthermophile Sulfolobus solfataricus, the increased melting temperature of the thermostable protein is due to a broadening as well as a significant lifting of its stability curve. However, at their physiological temperatures, 310K for mesophilic SH3 domains and 350K for Sso7d, eukaryotic SH3 domains and Sso7d show very similar stabilities. (C) 1998 Wiley-Liss, Inc.
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| 65. |
- Knobe, Karin, et al.
(author)
-
Probing the activation of protein C by the thrombin-thrombomodulin complex using structural analysis, site-directed mutagenesis, and computer modeling
- 1999
-
In: Proteins. - 0887-3585. ; 35:2, s. 218-234
-
Journal article (peer-reviewed)abstract
- Protein C (PC) is activated to an essential anticoagulant enzyme (activated PC or APC) by thrombin (T) bound to thrombomodulin (TM), a membrane receptor present on the surface of endothelial cells. The understanding of this complex biological system is in part limited due to the lack of integration of experimental and structural data. In the work presented here, we analyze the PC-T-TM pathway in the context of both types of information. First, structural analysis of the serine protease domain of PC suggests that a positively charged cluster of amino acids could be involved in the activation process. To investigate the importance of these basic amino acids, two recombinant PC mutants were constructed using computer-guided site-directed mutagenesis. The double mutant had the K62[217]N/K63[218]D substitution and in the single mutant, K86[241] was changed to S. Both mutants were activated by free thrombin at rates equivalent to that of wild-type PC (wt-PC) and they demonstrated similar calcium-dependent inhibition of their activation. The K86[241]S mutant and wt-PC were activated by thrombin bound to soluble TM at a similar rate. In contrast, the K62[217]N/ K63[218]D mutant was activated by the T-TM complex at a 10-fold lower catalytic efficiency due to a lowering in k(cat) and increase in Km. Molecular models for PC and thrombin bound to a segment of TM were developed. The experimental results and the modeling data both indicate that electrostatic interactions are of crucial importance to orient PC onto the T-TM complex. A key electropositive region centered around loops 37[191] and 60[214] of PC is defined. PC loop 37[191] is located 7-8 A from the TM epidermal growth factor (EGF) 4 while the loop 60[214] is about 10 A away from TM EGF4. Both loops are far from thrombin. A key function of TM could be to create an additional binding site for PC. The Gla domain of PC points toward the membrane and away from thrombin or the EGF modules of TM during the activation process.
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| 66. |
- Kontijevskis, Aleksejs, et al.
(author)
-
Computational proteomics analysis of HIV-1 protease interactome
- 2007
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 68:1, s. 305-312
-
Journal article (peer-reviewed)abstract
- HIV-1 protease is a small homodimeric enzyme that ensures maturation of HIV virions by cleaving the viral precursor Gag and Gag-Pol polyproteins into structural and functional elements. The cleavage sites in the viral polyproteins share neither sequence homology nor binding motif and the specificity of the HIV-1 protease is therefore only partially understood. Using an extensive data set collected from 16 years of HIV proteome research we have here created a general and predictive rule-based model for HIV-1 protease specificity based on rough sets. We demonstrate that HIV-1 protease specificity is much more complex than previously anticipated, which cannot be defined based solely on the amino acids at the substrate's scissile bond or by any other single substrate amino acid position only. Our results show that the combination of at least three particular amino acids is needed in the substrate for a cleavage event to occur. Only by combining and analyzing massive amounts of HIV proteome data it was possible to discover these novel and general patterns of physico-chemical substrate cleavage determinants. Our study is an example how computational biology methods can advance the understanding of the viral interactomes.
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| 67. |
- Kontijevskis, Aleksejs, et al.
(author)
-
Proteochemometric analysis of small cyclic peptides' interaction with wild-type and chimeric melanocortin receptors
- 2007
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 69:1, s. 83-96
-
Journal article (peer-reviewed)abstract
- The melanocortin (MC) system confines unique G-protein coupled receptor pathways, which include the MC1-5 receptors and their endogenous agonists and antagonists, the MCs and the agouti and agouti-related proteins. The MC4 receptor is an important target for development of drugs for treatment of obesity and cachexia. While natural MC peptides are selective for the MC1 receptor, some cyclic pentapeptides, such as the HS-129 peptide, show high selectivity for the MC4 receptor. Here we gained insight into the mechanisms for its recognition by MC receptors. To this end we correlated the interaction data of four HS peptide analogues with four wild-type and 14 multiple chimeric MC receptors to the binary and physicochemical descriptions of the studied entities by use of partial least squares regression, which resulted in highly valid proteochemometric models. Analysis of the models revealed that the recognition sites of the HS peptides are different from the earlier proteochemometrically mapped linear MSH peptides' recognitions sites, although they overlap partially. The analysis also revealed important amino acids that explain the selectivity of the HS-129 peptide for the MC4 receptor.
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| 68. |
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| 69. |
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| 70. |
- Kulkarni, Tejas, et al.
(author)
-
Crystal structure of β-glucosidase 1A from Thermotoga neapolitana and comparison of active site mutants for hydrolysis of flavonoid glucosides
- 2017
-
In: Proteins: Structure, Function and Bioinformatics. - : Wiley. - 1097-0134 .- 0887-3585. ; 85:5, s. 872-884
-
Journal article (peer-reviewed)abstract
- The β-glucosidase TnBgl1A catalyses hydrolysis of O-linked terminal β-glycosidic bonds at the nonreducing end of glycosides/oligosaccharides. Enzymes with this specificity have potential in lignocellulose conversion (degrading cellobiose to glucose) and conversion of bioactive flavonoids (modification of glycosylation results in modulation of bioavailability). Previous work has shown TnBgl1A to hydrolyse 3, 4′ and 7 glucosylation in flavonoids, and although conversion of 3-glucosylated substrate to aglycone was low, it was improved by mutagenesis of residue N220. To further explore structure-function relationships, the crystal structure of the nucleophile mutant TnBgl1A-E349G was determined at 1.9 Å resolution, and docking studies of flavonoid substrates were made to reveal substrate interacting residues. A series of single amino acid changes were introduced in the aglycone binding region [N220(S/F), N221(S/F), F224(I), F310(L/E), and W322(A)] of the wild type. Activity screening was made on eight glucosylated flavonoids, and kinetic parameters were monitored for the flavonoid quercetin-3-glucoside (Q3), as well as for the model substrate para-nitrophenyl-β-d-glucopyranoside (pNPGlc). Substitution by Ser at N220 or N221 increased the catalytic efficiency on both pNPGlc and Q3. Residue W322 was proven important for substrate accomodation, as mutagenesis to W322A resulted in a large reduction of hydrolytic activity on 3-glucosylated flavonoids. Flavonoid glucoside hydrolysis was unaffected by mutations at positions 224 and 310. The mutations did not significantly affect thermal stability, and the variants kept an apparent unfolding temperature of 101°C. This work pinpoints positions in the aglycone region of TnBgl1A of importance for specificity on flavonoid-3-glucosides, improving the molecular understanding of activity in GH1 enzymes.
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| 71. |
- Kumar, Niti, et al.
(author)
-
Intrinsically disordered protein from a pathogenic mesophile Mycobacterium tuberculosis adopts structured conformation at high temperature.
- 2008
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 71:3, s. 1123-33
-
Journal article (peer-reviewed)abstract
- Compared to eukaryotes, the occurrence of "intrinsically disordered" or "natively unfolded" proteins in prokaryotes has not been explored extensively. Here, we report the occurrence of an intrinsically disordered protein from the mesophilic human pathogen Mycobacterium tuberculosis. The Histidine-tagged recombinant Rv3221c biotin-binding protein is intrinsically disordered at ambient and physiological growth temperatures as revealed by circular dichroism and Fourier transform infrared (FTIR) spectroscopic studies. However, an increase in temperature induces a transition from disordered to structured state with a folding temperature of approximately 53 degrees C. Addition of a structure inducing solvent trifluoroethanol (TFE) causes the protein to fold at lower temperatures suggesting that TFE fosters hydrophobic interactions, which drives protein folding. Differential Scanning Calorimetry studies revealed that folding is endothermic and the transition from a disordered to structured state is continuous (higher-order), implying existence of intermediates during folding process. Secondary structure analysis revealed that the protein has propensity to form beta-sheets. This is in conformity with FTIR spectrum that showed an absorption peak at wave number of 1636 cm(-1), indicative of disordered beta-sheet conformation in the native state. These data suggest that although Rv3221c may be disordered under ambient or optimal growth temperature conditions, it has the potential to fold into ordered structure at high temperature driven by increased hydrophobic interactions. In contrast to the generally known behavior of other intrinsically disordered proteins folding at high temperature, Rv3221c does not appear to oligomerize or aggregate as revealed through numerous experiments including Congo red binding, Thioflavin T-binding, turbidity measurements, and examining molar ellipticity as a function of protein concentration. The amino acid composition of Rv3221c reveals that it has 24% charged and 54.9% hydrophobic amino acid residues. In this respect, this protein, although belonging to the class of intrinsically disordered proteins, has distinct features. The intrinsically disordered state and the biotin-binding feature of this protein suggest that it may participate in many biochemical processes requiring biotin as a cofactor and adopt suitable conformations upon binding other folded targets.
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| 72. |
- Kurut Sabanoglu, Anil, et al.
(author)
-
Role of histidine for charge regulation of unstructured peptides at interfaces and in bulk.
- 2014
-
In: Proteins. - : Wiley. - 0887-3585. ; 82:4, s. 657-667
-
Journal article (peer-reviewed)abstract
- Histidine rich, unstructured peptides adsorb to charged interfaces such as mineral surfaces and microbial cell membranes. At a molecular level, we investigate the adsorption mechanism as a function of pH, salt, and multivalent ions showing that (1) proton charge fluctuations are - in contrast to the majority of proteins - optimal at neutral pH, promoting electrostatic interactions with anionic surfaces through charge regulation, and (2) specific zinc(II)-histidine binding competes with protons and ensures an unusually constant charge distribution over a broad pH interval. In turn this further enhances surface adsorption. Our analysis is based on atomistic molecular dynamics simulations, coarse grained Metropolis Monte Carlo, and classical polymer density functional theory. This multi-scale modelling provides a consistent picture in good agreement with experimental data on Histatin 5, an antimicrobial salivary peptide. Biological function is discussed and we suggest that charge regulation is a significant driving force for the remarkably robust activity of histidine rich antimicrobial peptides.
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| 73. |
- Laine, Elodie, et al.
(author)
-
Protein sequence-to-structure learning : Is this the end(-to-end revolution)?
- 2021
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 89:12, s. 1770-1786
-
Research review (peer-reviewed)abstract
- The potential of deep learning has been recognized in the protein structure prediction community for some time, and became indisputable after CASP13. In CASP14, deep learning has boosted the field to unanticipated levels reaching near-experimental accuracy. This success comes from advances transferred from other machine learning areas, as well as methods specifically designed to deal with protein sequences and structures, and their abstractions. Novel emerging approaches include (i) geometric learning, that is, learning on representations such as graphs, three-dimensional (3D) Voronoi tessellations, and point clouds; (ii) pretrained protein language models leveraging attention; (iii) equivariant architectures preserving the symmetry of 3D space; (iv) use of large meta-genome databases; (v) combinations of protein representations; and (vi) finally truly end-to-end architectures, that is, differentiable models starting from a sequence and returning a 3D structure. Here, we provide an overview and our opinion of the novel deep learning approaches developed in the last 2 years and widely used in CASP14.
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| 74. |
- Lapinsh, Maris, et al.
(author)
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Proteochemometric modeling reveals the interaction site for Trp9 modified alpha-MSH peptides in melanocortin receptors
- 2007
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 67:3, s. 653-660
-
Journal article (peer-reviewed)abstract
- The interactions of α-MSH peptides with melanocortin receptors (MCRs) were located by proteochemometric modeling. Nine α-MSH peptide analogues were constructed by exchanging the Trp9 residue in the α-MSH core with the natural or artificial amino acids Arg, Asp, Cys, Gly, Leu, Nal, d-Nal, Pro, or d-Trp. The nine peptides created, and α-MSH itself, were evaluated for their interactions with the 4 wild-type MC1,3-5Rs and 15 multichimeric MCRs, each of the latter being constructed from three sequence segments, each taken from a different wild-type MC1,3-5R. The segments of the chimeric MCRs were selected according to the principles of statistical molecular design and were arranged so as to divide the receptors into five parts. By this approach, a set of 19 maximally diverse MC receptor proteins was obtained for which the interaction activity with the 10 peptides were measured by radioligand binding thus creating data for 190 ligand-protein pairs, which were subsequently analyzed by use of proteochemometric modeling. In proteochemometrics, the structural or physicochemical properties of both interaction partners, which represent the complementarity of the interacting entities, are used to create multivariate mathematical descriptions. (Here, physicochemical property descriptors of the receptors' and peptides' amino acids were used). A valid, highly predictive (Q2 = 0.74) and easily interpretable model was then obtained. The model was further validated by its ability to correctly predicting the affinity of α-MSH for new point and cassette-mutated MC4/MC1RS, and it was then used to identify the receptor residues that are important for affording the high affinity and selectivity of α-MSH for the MC1R. It was revealed that these residues are located in several quite distant parts of the receptors' transmembrane cavity and must therefore cause their influence at various stages of the dynamic ligand-binding process, such as by affecting the conformation of the ligand at the vicinity of the receptor and taking part in the path of the ligand's entry into its binding pocket. Our study can be used as a template how to create high resolution proteochemometric models when there are a limited number of natural proteins and ligands available.
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| 75. |
- Larsson, Per, et al.
(author)
-
Assessment of global and local model quality in CASP8 using Pcons and ProQ
- 2009
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 77:9, s. 167-172
-
Journal article (peer-reviewed)abstract
- Model Quality Assessment Programs (MQAPs) are programs developed to rank protein models. These methods can be trained to predict the overall global quality of a model or what local regions in a model that are likely to be incorrect. In CASP8, we participated with two predictors that predict both global and local quality using either consensus information, Pcons, or purely structural information, ProQ. Consistently with results in previous CASPs, the best performance in CASP8 was obtained using the Pcons method. Furthermore, the results show that the modification introduced into Pcons for CASP8 improved the predictions against GDT_TS and now a correlation coefficient above 0.9 is achieved, whereas the correlation for ProQ is about 0.7. The correlation is better for the easier than for the harder targets, but it is not below 0.5 for a single target and below 0.7 only for three targets. The correlation coefficient for the best local quality MQAP is 0.68 showing that there is still clear room for improvement within this area. We also detect that Pcons still is not always able to identify the best model. However, we show that using a linear combination of Pcons and ProQ it is possible to select models that are better than the models from the best single server. In particular, the average quality over the hard targets increases by about 6% compared with using Pcons alone.
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| 76. |
- Lehtio, J., et al.
(author)
-
Alpha-amylase inhibitors selected from a combinatorial library of a cellulose binding domain scaffold
- 2000
-
In: Proteins. - 0887-3585 .- 1097-0134. ; 41:3, s. 316-322
-
Journal article (peer-reviewed)abstract
- A disulfide bridge-constrained cellulose binding domain (CBD,) derived from the cellobiohydrolase Ce17A from Trichoderma reesei has been investigated for use in scaffold engineering to obtain novel binding proteins. The gene encoding the wild-type 36 aa CBDWT domain was first inserted into a phagemid vector and shown to be functionally displayed on M13 filamentous phage as a protein III fusion protein with retained cellulose binding activity. A combinatorial library comprising 46 million variants of the CBD domain was constructed through randomization of 11 positions located at the domain surface and distributed over three separate beta -sheets of the domain. Using the enzyme porcine alpha-amylase (PPA) as target in biopannings, two CBD variants showing selective binding to the enzyme were characterized. Reduction and iodoacetamide blocking of cysteine residues in selected CBD variants resulted in a loss of binding activity, indicating a conformation dependent binding. Interestingly, further studies showed that the selected CBD variants were capable of competing with the binding of the amylase inhibitor acarbose to the enzyme. In addition, the enzyme activity could be partially inhibited by addition of soluble protein, suggesting that the selected CBD variants bind to the active site of the enzyme.
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| 77. |
- Lensink, Marc F., et al.
(author)
-
Impact of AlphaFold on structure prediction of protein complexes: The CASP15-CAPRI experiment
- 2023
-
In: Proteins. - : WILEY. - 0887-3585 .- 1097-0134.
-
Journal article (peer-reviewed)abstract
- We present the results for CAPRI Round 54, the 5th joint CASP-CAPRI protein assembly prediction challenge. The Round offered 37 targets, including 14 homodimers, 3 homo-trimers, 13 heterodimers including 3 antibody-antigen complexes, and 7 large assemblies. On average similar to 70 CASP and CAPRI predictor groups, including more than 20 automatics servers, submitted models for each target. A total of 21 941 models submitted by these groups and by 15 CAPRI scorer groups were evaluated using the CAPRI model quality measures and the DockQ score consolidating these measures. The prediction performance was quantified by a weighted score based on the number of models of acceptable quality or higher submitted by each group among their five best models. Results show substantial progress achieved across a significant fraction of the 60+ participating groups. High-quality models were produced for about 40% of the targets compared to 8% two years earlier. This remarkable improvement is due to the wide use of the AlphaFold2 and AlphaFold2-Multimer software and the confidence metrics they provide. Notably, expanded sampling of candidate solutions by manipulating these deep learning inference engines, enriching multiple sequence alignments, or integration of advanced modeling tools, enabled top performing groups to exceed the performance of a standard AlphaFold2-Multimer version used as a yard stick. This notwithstanding, performance remained poor for complexes with antibodies and nanobodies, where evolutionary relationships between the binding partners are lacking, and for complexes featuring conformational flexibility, clearly indicating that the prediction of protein complexes remains a challenging problem.
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| 78. |
- Linhult, M., et al.
(author)
-
Improving the tolerance of a protein a analogue to repeated alkaline exposures using a bypass mutagenesis approach
- 2004
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 55:2, s. 407-416
-
Journal article (peer-reviewed)abstract
- Staphylococcal protein A (SPA) is a cell surface protein expressed by Staphylococcus aureus. It consists of five repetitive domains. The five SPA-domains show individual interaction to the Fc-fragment as well as certain Fab-fragments of immunoglobulin G (IgG) from most mammalian species. Due to the high affinity and selectivity of SPA, it has a widespread use as an affinity ligand for capture and purification of antibodies. One of the problems with proteinaceous affinity ligands in large-scale purification is their sensitivity to alkaline conditions. SPA however, is considered relatively stable to alkaline treatment. Nevertheless, it is desirable to further improve the stability in order to enable an SPA-based affinity medium to withstand even longer exposure to the harsh conditions associated with cleaning-in-place (CIP) procedures. For this purpose, a protein engineering strategy, which was used earlier for stabilization and consists of replacing the asparagine residues, is employed. Since Z in its nonengineered form already has a significant tolerance to alkaline treatment, small changes in stability due to the mutations are difficult to assess. Hence, in order to enable detection of improvements regarding the alkaline resistance of the Z domain, we chose to use a bypass mutagenesis strategy using a mutated variant Z(F30A) as a surrogate framework. Z(F30A) has earlier been shown to possess an affinity to IgG that is similar to the wild-type but also demonstrates decreased structural stability. Since the contribution of the different asparagine residues to the deactivation rate of a ligand is dependent on the environment and also the structural flexibility of the particular region, it is important to consider all sensitive amino acids one by one. The parental Z-domain contains eight asparagine residues, each with a different impact on the alkaline stability of the domain. By exchanging asparagine 23 for a threonine, we were able to increase the stability of the Z(F30A) domain in alkaline conditions. Also, when grafting the N23T mutation to the Z scaffold, we were able to detect an increased tolerance to alkaline treatment compared to the native Z molecule.
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| 79. |
- Lubovac, Zelmina, et al.
(author)
-
Combining functional and topological properties to identify core modules in protein interaction networks
- 2006
-
In: Proteins. - : John Wiley & Sons. - 0887-3585 .- 1097-0134. ; 64:4, s. 948-959
-
Journal article (peer-reviewed)abstract
- Advances in large-scale technologies in proteomics, such as yeast two-hybrid screening and mass spectrometry, have made it possible to generate large Protein Interaction Networks (PINs). Recent methods for identifying dense sub-graphs in such networks have been based solely on graph theoretic properties. Therefore, there is a need for an approach that will allow us to combine domain-specific knowledge with topological properties to generate functionally relevant sub-graphs from large networks. This article describes two alternative network measures for analysis of PINs, which combine functional information with topological properties of the networks. These measures, called weighted clustering coefficient and weighted average nearest-neighbors degree, use weights representing the strengths of interactions between the proteins, calculated according to their semantic similarity, which is based on the Gene Ontology terms of the proteins. We perform a global analysis of the yeast PIN by systematically comparing the weighted measures with their topological counterparts. To show the usefulness of the weighted measures, we develop an algorithm for identification of functional modules, called SWEMODE (Semantic WEights for MODule Elucidation), that identifies dense sub-graphs containing functionally similar proteins. The proposed method is based on the ranking of nodes, i.e., proteins, according to their weighted neighborhood cohesiveness. The highest ranked nodes are considered as seeds for candidate modules. The algorithm then iterates through the neighborhood of each seed protein, to identify densely connected proteins with high functional similarity, according to the chosen parameters. Using a yeast two-hybrid data set of experimentally determined protein-protein interactions, we demonstrate that SWEMODE is able to identify dense clusters containing proteins that are functionally similar. Many of the identified modules correspond to known complexes or subunits of these complexes.
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| 80. |
- Luo, Jinghui, et al.
(author)
-
Examining the promiscuous phosphatase activity of Pseudomonas aeruginosa arylsulfatase : A comparison to analogous phosphatases
- 2012
-
In: Proteins: Structure, Function and Bioinformatics. - : Wiley. - 1097-0134 .- 0887-3585. ; 80:4, s. 1211-1226
-
Journal article (peer-reviewed)abstract
- Pseudomonas aeruginosa arylsulfatase (PAS) is a bacterial sulfatase capable ofhydrolyzing a range of sulfate esters. Recently, it has been demonstrated to also show very high proficiency for phosphate ester hydrolysis. Such proficient catalytic promiscuity is significant, as promiscuity has been suggested to play an important role in enzyme evolution. Additionally, a comparative study of the hydrolyses of the p-nitrophenyl phosphate and sulfate monoesters in aqueous solution has demonstrated that despite superficial similarities, the two reactions proceed through markedly different transition states with very different solvation effects, indicating that the requirements for the efficient catalysis of the two reactions by an enzyme will also be very different (and yet they are both catalyzed by thesame active site). This work explores the promiscuous phosphomonoesterase activity ofPAS. Specifically, we have investigated the identity of the most likely base for the initial activation of the unusual formylglycine hydrate nucleophile (which is common to many sulfatases), and demonstrate that a concerted substrate-as-base mechanism is fully consistent with the experimentally observed data. This is very similar to other related systems, and suggests that, as far as the phosphomonoesterase activity of PAS is concerned, the sulfatase behaves like a classical phosphatase, despite the fact that such a mechanism is unlikely to be available to the native substrate (based on pKa considerations and studies of model systems). Understanding such catalytic versatility can be used to design novel artificial enzymes that are far more proficient than the current generation ofdesigner enzymes.
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| 81. |
- Magnusdottir, Audur, et al.
(author)
-
The structure of the PP2A regulatory subunit B56gamma : The remaining piece of the PP2A jigsaw puzzle
- 2009
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 74:1, s. 212-221
-
Journal article (peer-reviewed)abstract
- The PP2A serine/threonine phosphatase regulates a plethora of cellular processes. In the cell the predominant form of the enzyme is a heterotrimer, formed by a core dimer composed of a catalytic and a scaffolding subunit, which assemble together with one of a range of different regulatory B subunits. Here, we present the first structure of a free non-complexed B subunit, B56. Comparison with the recent structures of a heterotrimeric complex and the core dimer reveals several significant conformational changes in the interface region between the B56 and the core dimer. These allow for an assembly scheme of the PP2A holoenzyme to be put forth where B56 first complexes with the scaffolding subunit and subsequently binds to the catalytic subunit and this induces the formation of a binding site for the invariant C-terminus of the catalytic subunit that locks in the complex as a last step of assembly.
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| 82. |
- Mark, Pekka, et al.
(author)
-
Analysis of nasturtium TmNXG1 complexes by crystallography and molecular dynamics provides detailed insight into substrate recognition by family GH16 xyloglucan endo-transglycosylases and endo-hydrolases
- 2009
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 75:4, s. 820-836
-
Journal article (peer-reviewed)abstract
- Reorganization and degradation of the wall crosslinking and seed storage polysaccharide xyloglucan by glycoside hydrolase family 16 (GH16) endo-transglycosylases and hydrolases are crucial to the growth of the majority of land plants, affecting processes as diverse as germination, morphogenesis, and fruit ripening. A high-resolution, three-dimensional structure of a nasturtium (Tropaeolum majus) endo-xyloglucanase loop mutant, TmNXG1-Delta YNIIG, with an ohgosaccharide product bound in the negative active-site subsites, has been solved by X-ray crystallography. Comparison of this novel complex to that of the strict xyloglucan endotransglycosylase PttXET16-34 from hybrid aspen (Populus tremula x tremuloides), previously solved with a xylogluco-oligosaccharide bound in the positive subsites, highlighted key protein structures that affect the disparate catalytic activities displayed by these closely related enzymes. Combination of these "partial" active-site complexes through molecular dynamics simulations in water allowed modeling of wild-type TmNXG1, TmNXG1-Delta YNIIG, and wild-type PttXET16-34 in complex with a xyloglucan octadecasaccharide spanning the entire catalytic cleft. A comprehensive analysis of these full-length complexes underscored the importance of various loops lining the active site. Subtle differences leading to a tighter hydrogen bonding pattern on the negative (glycosyl donor) binding subsites, together with loop flexibility on the positive (glycosyl acceptor) binding subsites appear to favor hydrolysis over transglycosylation in GH16 xyloglucan-active enzymes.
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| 83. |
- Mirabello, Claudio, et al.
(author)
-
InterPred: A pipeline to identify and model protein-protein interactions
- 2017
-
In: Proteins. - : WILEY. - 0887-3585 .- 1097-0134. ; 85:6, s. 1159-1170
-
Journal article (peer-reviewed)abstract
- Protein-protein interactions (PPI) are crucial for protein function. There exist many techniques to identify PPIs experimentally, but to determine the interactions in molecular detail is still difficult and very time-consuming. The fact that the number of PPIs is vastly larger than the number of individual proteins makes it practically impossible to characterize all interactions experimentally. Computational approaches that can bridge this gap and predict PPIs and model the interactions in molecular detail are greatly needed. Here we present InterPred, a fully automated pipeline that predicts and model PPIs from sequence using structural modeling combined with massive structural comparisons and molecular docking. A key component of the method is the use of a novel random forest classifier that integrate several structural features to distinguish correct from incorrect protein-protein interaction models. We show that InterPred represents a major improvement in protein-protein interaction detection with a performance comparable or better than experimental high-throughput techniques. We also show that our full-atom protein-protein complex modeling pipeline performs better than state of the art protein docking methods on a standard benchmark set. In addition, InterPred was also one of the top predictors in the latest CAPRI37 experiment. InterPred source code can be downloaded from http://wallnerlab.org/InterPred (C) 2017 Wiley Periodicals, Inc.
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| 84. |
- Mitternacht, Simon, et al.
(author)
-
Comparing the folding free-energy landscapes of Abeta42 variants with different aggregation properties.
- 2010
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 78:12, s. 2600-2608
-
Journal article (peer-reviewed)abstract
- The properties of the amyloid-beta peptide that lead to aggregation associated with Alzheimer's disease are not fully understood. This study aims at identifying conformational differences among four variants of full-length Abeta42 that are known to display very different aggregation properties. By extensive all-atom Monte Carlo simulations, we find that a variety of beta-sheet structures with distinct turns are readily accessible for full-length Abeta42. In the simulations, wild type (WT) Abeta42 preferentially populates two major classes of conformations, either extended with high beta-sheet content or more compact with lower beta-sheet content. The three mutations studied alter the balance between these classes. Strong mutational effects are observed in a region centered at residues 23-26, where WT Abeta42 tends to form a turn. The aggregation-accelerating E22G mutation associated with early onset of Alzheimer's disease makes this turn region conformationally more diverse, whereas the aggregation-decelerating F20E mutation has the reverse effect, and the E22G/I31E mutation reduces the turn population. Comparing results for the four Abeta42 variants, we identify specific conformational properties of residues 23-26 that might play a key role in aggregation. Proteins 2010. (c) 2010 Wiley-Liss, Inc.
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| 85. |
- Moretti, Rocco, et al.
(author)
-
Community-wide evaluation of methods for predicting the effect of mutations on protein-protein interactions
- 2013
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 81:11, s. 1980-1987
-
Journal article (peer-reviewed)abstract
- Community-wide blind prediction experiments such as CAPRI and CASP provide an objective measure of the current state of predictive methodology. Here we describe a community-wide assessment of methods to predict the effects of mutations on protein-protein interactions. Twenty-two groups predicted the effects of comprehensive saturation mutagenesis for two designed influenza hemagglutinin binders and the results were compared with experimental yeast display enrichment data obtained using deep sequencing. The most successful methods explicitly considered the effects of mutation on monomer stability in addition to binding affinity, carried out explicit side-chain sampling and backbone relaxation, evaluated packing, electrostatic, and solvation effects, and correctly identified around a third of the beneficial mutations. Much room for improvement remains for even the best techniques, and large-scale fitness landscapes should continue to provide an excellent test bed for continued evaluation of both existing and new prediction methodologies. Proteins 2013; 81:1980-1987.
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| 86. |
- Nandy, A., et al.
(author)
-
Homology model of the human tRNA splicing ligase RtcB
- 2017
-
In: Proteins-Structure Function and Bioinformatics. - : Wiley. - 0887-3585 .- 1097-0134. ; 85:11, s. 1983-1993
-
Journal article (peer-reviewed)abstract
- RtcB is an essential human tRNA ligase required for ligating the 2', 3'-cyclic phosphate and 5'-hydroxyl termini of cleaved tRNA halves during tRNA splicing and XBP1 fragments during endoplasmic reticulum stress. Activation of XBP1 has been implicated in various human tumors including breast cancer. Here we present, for the first time, a homology model of human RtcB (hRtcB) in complex with manganese and covalently bound GMP built from the Pyrococcus horikoshii RtcB (bRtcB) crystal structure, PDB ID 4DWQA. The structure is analyzed in terms of stereochemical quality, folding reliability, secondary structure similarity with bRtcB, druggability of the active site binding pocket and its metal-binding microenvironment. In comparison with bRtcB, loss of a manganese-coordinating water and movement of Asn226 (Asn202 in 4DWQA) to form metal-ligand coordination, demonstrates the uniqueness of the hRtcB model. Rotation of GMP leads to the formation of an additional metal-ligand coordination (Mn-O). Umbrella sampling simulations of Mn binding in wild type and the catalytically inactive C122A mutant reveal a clear reduction of Mn binding ability in the mutant, thus explaining the loss of activity therein. Our results furthermore clearly show that the GTP binding site of the enzyme is a well-defined pocket that can be utilized as target site for in silico drug discovery.
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| 87. |
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| 88. |
- Nivón, Lucas G, et al.
(author)
-
Automating human intuition for protein design
- 2014
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 82:5, s. 858-866
-
Journal article (peer-reviewed)abstract
- In the design of new enzymes and binding proteins, human intuition is often used to modify computationally designed amino acid sequences prior to experimental characterization. The manual sequence changes involve both reversions of amino acid mutations back to the identity present in the parent scaffold and the introduction of residues making additional interactions with the binding partner or backing up first shell interactions. Automation of this manual sequence refinement process would allow more systematic evaluation and considerably reduce the amount of human designer effort involved. Here we introduce a benchmark for evaluating the ability of automated methods to recapitulate the sequence changes made to computer-generated models by human designers, and use it to assess alternative computational methods. We find the best performance for a greedy one-position-at-a-time optimization protocol that utilizes metrics (such as shape complementarity) and local refinement methods too computationally expensive for global Monte Carlo (MC) sequence optimization. This protocol should be broadly useful for improving the stability and function of designed binding proteins.
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| 89. |
- Permyakov, Eugene A, et al.
(author)
-
Ultraviolet illumination-induced reduction of alpha-lactalbumin disulfide bridges
- 2003
-
In: Proteins: Structure, Function, and Bioinformatics. - : Wiley. - 0887-3585. ; 51:4, s. 498-503
-
Journal article (peer-reviewed)abstract
- Prolonged exposure of Ca2+-loaded or Ca2+-depleted human -lactalbumin to ultraviolet light (270-290 nm, 1 mW/cm2, for 2 to 4 h) results in a 10-nm red shift of its tryptophan fluorescence spectrum. Gel chromatography of the UV-illuminated samples reveals two non-native protein forms: (1) a component with a red-shifted tryptophan fluorescence spectrum; and (2) a component with kynurenine-like fluorescent properties. The first component has from 0.6 to 0.9 free DTNB-reactive SH groups per protein molecule, which are absent in the native protein and is characterized by slightly lowered Ca2+-affinity (2 × 108 M-1 versus 8 × 108 M-1 for the native protein) and absence of observable thermal transition. The second component corresponds to the protein with photochemically modified tryptophan residues. It is assumed that the UV excitation of tryptophan residue(s) in -lactalbumin is followed by a transfer of electrons to the SS bonds, resulting in their reduction. Mass spectrometry data obtained for trypsin-fragmented UV-illuminated -lactalbumin with acrylodan-modified free thiol groups reveal the reduction of the 61-77 and 73-91 disulfide bridges. The effect observed has to be taken into account in any UV-region spectral studies of -lactalbumin. Proteins 2003;51:498-503.
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| 90. |
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| 91. |
- Peters, Christoph, et al.
(author)
-
Why is the biological hydrophobicity scale more accurate than earlier experimental hydrophobicity scales?
- 2014
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 82:9, s. 2190-2198
-
Journal article (peer-reviewed)abstract
- The recognition of transmembrane helices by the translocon is primarily guided by the average hydrophobicity of the protential transmembrane helix, However, he exact hydrophobicity of each amino acid can he identified in several diferent ways. The free energy of transfer for amino acid analogues between a hydrophobic media, for example, octanol and water can be measured or obtained from simulations, the hydrophobicity can also be estimated by statistical properties from known transmembrane segments and finally the contribution of each amino acid type for the probability of traitslocon recognition has recently been measured directly. Although these scales correlate quite well, there are dear differences between them and it is not well understood which scale represents neither the biology best nor what the differences are. Here, we try to provide some answers to this by studying the ability of different scales to recognize transmembrane helices and predict the topology of transmembrane proteins. From this analysis it is clear that the biological hydrophobicity scale as well scales created from statistical analysis of membrane helices perform better than earlier experimental scales that are mainly based on measurements of amino acid analogs and not directly on transmeiribrane helix recognition. Using these results we identified the properties of the scales that perform better than other scales. We find, for instance, that the better performing scales consider proline more hydrophilic. This shows that tratismembrarie recognition is not only governed by pure hydrophobicity but also by the helix preferences for amino acids, as praline is a strong helix breaker.
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| 92. |
- Pozzati, Gabriele, et al.
(author)
-
Scoring of protein-protein docking models utilizing predicted interface residues
- 2022
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 90:7, s. 1493-1505
-
Journal article (peer-reviewed)abstract
- Scoring docking solutions is a difficult task, and many methods have been developed for this purpose. In docking, only a handful of the hundreds of thousands of models generated by docking algorithms are acceptable, causing difficulties when developing scoring functions. Today's best scoring functions can significantly increase the number of top-ranked models but still fail for most targets. Here, we examine the possibility of utilizing predicted interface residues to score docking models generated during the scan stage of a docking algorithm. Many methods have been developed to infer the regions of a protein surface that interact with another protein, but most have not been benchmarked using docking algorithms. This study systematically tests different interface prediction methods for scoring >300.000 low-resolution rigid-body template free docking decoys. Overall we find that contact-based interface prediction by BIPSPI is the best method to score docking solutions, with >12% of first ranked docking models being acceptable. Additional experiments indicated precision as a high-importance metric when estimating interface prediction quality, focusing on docking constraints production. Finally, we discussed several limitations for adopting interface predictions as constraints in a docking protocol.
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| 93. |
- Rath, Emma M, et al.
(author)
-
Small-angle X-ray scattering of BAMLET at pH 12 : a complex of α-lactalbumin and oleic acid
- 2014
-
In: Proteins. - : Wiley. - 0887-3585. ; 82:7, s. 8-1400
-
Journal article (peer-reviewed)abstract
- BAMLET (Bovine Alpha-lactalbumin Made LEthal to Tumors) is a member of the family of the HAMLET-like complexes, a novel class of protein-based anti-cancer complexes that incorporate oleic acid and deliver it to cancer cells. Small angle X-ray scattering (SAXS) was performed on the complex at pH 12, examining the high pH structure as a function of oleic acid added. The SAXS data for BAMLET species prepared with a range of oleic acid concentrations indicate extended, irregular, partially unfolded protein conformations that vary with the oleic acid concentration. Increases in oleic acid concentration correlate with increasing radius of gyration without an increase in maximum particle dimension, indicating decreasing protein density. The models for the highest oleic acid content BAMLET indicate an unusual coiled elongated structure that contrasts with apo-α-lactalbumin at pH 12, which is an elongated globular molecule, suggesting that oleic acid inhibits the folding or collapse of the protein component of BAMLET to the globular form. Circular dichroism of BAMLET and apo-α-lactalbumin was performed and the results suggest that α-lactalbumin and BAMLET unfold in a continuum of increasing degree of unfolded states. Taken together, these results support a model in which BAMLET retains oleic acid by non-specific association in the core of partially unfolded protein, and represent a new type of lipoprotein structure.
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| 94. |
- Repic, Matej, et al.
(author)
-
Empirical valence bond simulations of the hydride transfer step in the monoamine oxidase B catalyzed metabolism of dopamine
- 2014
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 82:12, s. 3347-3355
-
Journal article (peer-reviewed)abstract
- Monoamine oxidases (MAOs) A and B are flavoenzymes responsible for the metabolism of biogenic amines such as dopamine, serotonin and noradrenaline. In this work, we present a comprehensive study of the rate-limiting step of dopamine degradation by MAO B, which consists in the hydride transfer from the methylene group of the substrate to the flavin moiety of the FAD prosthetic group. This article builds on our previous quantum chemical study of the same reaction using a cluster model (Vianello et al., Eur J Org Chem 2012; 7057), but now considering the full dimensionality of the hydrated enzyme with extensive configurational sampling. We show that MAO B is specifically tuned to catalyze the hydride transfer step from the substrate to the flavin moiety of the FAD prosthetic group and that it lowers the activation barrier by 12.3 kcal mol(-1) compared to the same reaction in aqueous solution, a rate enhancement of more than nine orders of magnitude. Taking into account the deprotonation of the substrate prior to the hydride transfer reaction, the activation barrier in the enzyme is calculated to be 16.1 kcal mol(-1), in excellent agreement with the experimental value of 16.5 kcal mol(-1). Additionally, we demonstrate that the protonation state of the active site residue Lys296 does not have an influence on the hydride transfer reaction.
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| 95. |
- Rozman Grinberg, Inna, et al.
(author)
-
Distinctive ligand-binding specificities of tandem PA14 biomass-sensory elements from Clostridium thermocellum and Clostridium clariflavum
- 2019
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 87:11, s. 917-930
-
Journal article (peer-reviewed)abstract
- Cellulolytic clostridia use a highly efficient cellulosome system to degrade polysaccharides. To regulate genes encoding enzymes of the multi-enzyme cellulosome complex, certain clostridia contain alternative sigma I (sigma(I)) factors that have cognate membrane-associated anti-sigma(I) factors (RsgIs) which act as polysaccharide sensors. In this work, we analyzed the structure-function relationship of the extracellular sensory elements of Clostridium (Ruminiclostridium) thermocellum and Clostridium clariflavum (RsgI3 and RsgI4, respectively). These elements were selected for comparison, as each comprised two tandem PA14-superfamily motifs. The X-ray structures of the PA14 modular dyads from the two bacterial species were determined, both of which showed a high degree of structural and sequence similarity, although their binding preferences differed. Bioinformatic approaches indicated that the DNA sequence of promoter of sigI/rsgI operons represents a strong signature, which helps to differentiate binding specificity of the structurally similar modules. The sigma(I4)-dependent C. clariflavum promoter sequence correlates with binding of RsgI4_PA14 to xylan and was identified in genes encoding xylanases, whereas the sigma(I3)-dependent C. thermocellum promoter sequence correlates with RsgI3_PA14 binding to pectin and regulates pectin degradation-related genes. Structural similarity between clostridial PA14 dyads to PA14-containing proteins in yeast helped identify another crucial signature element: the calcium-binding loop 2 (CBL2), which governs binding specificity. Variations in the five amino acids that constitute this loop distinguish the pectin vs xylan specificities. We propose that the first module (PA14(A)) is dominant in directing the binding to the ligand in both bacteria. The two X-ray structures of the different PA14 dyads represent the first reported structures of tandem PA14 modules.
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| 96. |
- Rämisch, Sebastian, et al.
(author)
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Exploring alternate states and oligomerization preferences of coiled-coils by de novo structure modeling
- 2015
-
In: Proteins. - : Wiley. - 0887-3585. ; 83:2, s. 235-247
-
Journal article (peer-reviewed)abstract
- Homomeric coiled-coils can self-assemble into a wide range of structural states with different helix topologies and oligomeric states. In this study, we have combined de novo structure modeling with stability calculations to simultaneously predict structure and oligomeric states of homomeric coiled-coils. For dimers an asymmetric modeling protocol was developed. Modeling without symmetry constraints showed that backbone asymmetry is important for the formation of parallel dimeric coiled-coils. Collectively, our results demonstrate that high-resolution structure of coiled-coils, as well as parallel and antiparallel orientations of dimers and tetramers, can be accurately predicted from sequence. De novo modeling was also used to generate models of competing oligomeric states, which were used to compare stabilities and thus predict the native stoichiometry from sequence. In a benchmark set of 33 coiled-coil sequences, forming dimers to pentamers, up to 70% of the oligomeric states could be correctly predicted. The calculations demonstrated that the free energy of helix folding could be an important factor for determining stability and oligomeric state of homomeric coiled-coils. The computational methods developed here should be broadly applicable to studies of sequence-structure relationships in coiled-coils and the design of higher order assemblies with improved oligomerization specificity. This article is protected by copyright. All rights reserved.
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| 97. |
- Saenz Mendez, Patricia, et al.
(author)
-
Structural insights into human microsomal epoxide hydrolase by combined homology modeling, molecular dynamics simulations, and molecular docking calculations
- 2017
-
In: Proteins-Structure Function and Bioinformatics. - : Wiley. - 0887-3585 .- 1097-0134. ; 85:4, s. 720-730
-
Journal article (peer-reviewed)abstract
- A new homology model of human microsomal epoxide hydrolase was derived based on multiple templates. The model obtained was fully evaluated, including MD simulations and ensemble-based docking, showing that the quality of the structure is better than that of only previously known model. Particularly, a catalytic triad was clearly identified, in agreement with the experimental information available. Analysis of intermediates in the enzymatic mechanism led to the identification of key residues for substrate binding, stereoselectivity, and intermediate stabilization during the reaction. In particular, we have confirmed the role of the oxyanion hole and the conserved motif (HGXP) in epoxide hydrolases, in excellent agreement with known experimental and computational data on similar systems. The model obtained is the first one that fully agrees with all the experimental observations on the system. (C) 2017 Wiley Periodicals, Inc.
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| 98. |
- Sagemark, Johan, et al.
(author)
-
Redox properties and evolution of human glutaredoxins
- 2007
-
In: Proteins. - : Wiley. - 0887-3585 .- 1097-0134. ; 68:4, s. 879-892
-
Journal article (peer-reviewed)abstract
- Glutaredoxins (Grxs) are glutathione-dependent oxidoreductases that belong to the thioredoxin superfamily catalyzing thiol-disulfide exchange reactions via active site cysteine residues. Focusing on the human dithiol glutaredoxins having a C-X-Y-C active site sequence motif, the redox potentials of hGrxl and hGrx2 were determined to be -232 and -221 mV, respectively, using a combination of redox buffers, protein-protein equilibrium and thermodynamic linkage. In addition, a nonactive site disulfide was identified between Cys28 and Cys.113 in hGrx2 using redox buffers and chemical digestion. This disulfide confers nearly five kcal mol-1 additional stability by linking the C-terminal helix to the bulk of the protein. The redox potential of this nonactive site disulfide was determined to be -317 mVand is thus expected to be present in all but the most reducing conditions in vivo. As all human glutaredoxins contain additional nonactive site cysteine residues, a full phylogenetic analysis was performed to help elucidate their structural and functional roles. Three distinct groups were found: Grx1, Grx2, and Grx5, the latter representing a highly conserved group of monothiol glutaredoxins having a C-G-F-S active site sequence, with clear homologs from bacteria to human. Grx1 and Grx2 diverged from a common ancestor before the origin vertebrates, possibly even earlier in animal evolution. The highly stabilizing nonactive site disulfide observed in hGrx2 is found to be a conserved feature within the deuterostomes and appears to be the only additional conserved intramolecular disulfide within the glutaredoxins.
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| 99. |
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| 100. |
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