| 1. |
- Brown, Christian, et al.
(författare)
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Structural and functional characterization of the microtubule interacting and trafficking domains of two oomycete chitin synthases
- 2016
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Ingår i: The FEBS Journal. - : Wiley. - 1742-464X .- 1742-4658. ; 283:16, s. 3072-3088
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Tidskriftsartikel (refereegranskat)abstract
- Chitin synthases (Chs) are responsible for the synthesis of chitin, a key structural cell wall polysaccharide in many organisms. They are essential for growth in certain oomycete species, some of which are pathogenic to diverse higher organisms. Recently, a Microtubule Interacting and Trafficking (MIT) domain, which is not found in any fungal Chs, has been identified in some oomycete Chs proteins. Based on experimental data relating to the binding specificity of other eukaryotic MIT domains, there was speculation that this domain may be involved in the intracellular trafficking of Chs proteins. However, there is currently no evidence for this or any other function for the MIT domain in these enzymes. To attempt to elucidate their function, MIT domains from two Chs enzymes from the oomycete Saprolegnia monoica were cloned, expressed and characterized. Both were shown to interact strongly with the plasma membrane component phosphatidic acid, and to have additional putative interactions with proteins thought to be involved in protein transport and localization. Aiding our understanding of these data, the structure of the first MIT domain from a carbohydrate-active enzyme (MIT1) was solved by NMR, and a model structure of a second MIT domain (MIT2) was built by homology modelling. Our results suggest a potential function for these MIT domains in the intracellular transport and/or regulation of Chs enzymes in the oomycetes.
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| 2. |
- Cheng, J., et al.
(författare)
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Molecular switches of the κ opioid receptor triggered by 6′-GNTI and 5′-GNTI
- 2016
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- The κ opioid receptor (κOR) is a member of G-protein-coupled receptors, and is considered as a promising drug target for treating neurological diseases. κOR selective 6′-GNTI was proved to be a G-protein biased agonist, whereas 5′-GNTI acts as an antagonist. To investigate the molecular mechanism of how these two ligands induce different behaviors of the receptor, we built two systems containing the 5′-GNTI-κOR complex and the 6′-GNTI-κOR complex, respectively, and performed molecular dynamics simulations of the two systems. We observe that transmembrane (TM) helix 6 of the κOR rotates about 4.6° on average in the κOR-6′-GNTI complex. Detailed analyses of the simulation results indicate that E2976.58 and I2946.55 play crucial roles in the rotation of TM6. In the simulation of the κOR-5′-GNTI system, it is revealed that 5′-GNTI can stabilize TM6 in the inactive state form. In addition, the kink of TM7 is stabilized by a hydrogen bond between S3247.47 and the residue V691.42 on TM1.
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| 3. |
- Fu, Yao, et al.
(författare)
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Duet of Acetate and Water at the Defects of Metal-Organic Frameworks
- 2019
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 19:3, s. 1618-1624
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Tidskriftsartikel (refereegranskat)abstract
- Metal-organic frameworks (MOFs) are porous crystalline materials with promising applications in molecular adsorption, separation, and catalysis. It has been discovered recently that structural defects introduced unintentionally or by design could have a significant impact on their properties. However, the exact chemical composition and structural evolution under different conditions at the defects are still under debate. In this study, we performed multidimensional solid-state nuclear magnetic resonance (SSNMR) coupled with computer simulations to elucidate an important scenario of MOF defects, uncovering the dynamic interplay between residual acetate and water. Acetate, as a defect modulator, and water, as a byproduct, are prevalent defect-associated species, which are among the key factors determining the reactivity and stability of defects. We discovered that acetate molecules coordinate to a single metal site monodentately and pair with water at the neighboring position. The acetates are highly flexible, which undergo fast libration as well as a slow kinetic exchange with water through dynamic hydrogen bonds. The dynamic processes under variable temperatures and different hydration levels have been quantitatively analyzed across a broad time scale from microseconds to seconds. The integration of SSNMR and computer simulations allows a precision probe into defective MOF structures with intrinsic dynamics and disorder.
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| 4. |
- Guanglin, Kuang, 1987-
(författare)
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Theoretical Studies of Protein-Ligand Interactions
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The protein-ligand interaction is an important issue in rational drug design and protein function research. This thesis focuses on the study of protein-ligand interactions using various molecular modeling methods, which are used in combination to predict the binding modes and calculate the binding free energies of several important protein-ligand systems, as summarized below.In Paper I, we investigated the binding profile of a type I positive allosteric modulator (PAM) NS-1738 with the α7-nicotinic acetylcholine receptor (α7-nAChR). NS-1738 is found to have three different binding sites on α7-nAChR and has moderate binding affinities to the receptor.In Paper II, we revealed the binding mechanism of a PET radio-ligand [18F]ASEM with α7-nAChR. Using metadynamics simulations, we managed to find a stable state which is not observed in molecular docking and unbiased molecular dynamics simulations. Free energy analysis further confirmed that this stable state is the global minimum with respect to the selected collective variables.In Paper III, we studied the binding modes and binding affinities of two probes (AZD2184 and thioflavin T) for the detection of amyloid β(1-42) fibrils in clinical studies. We found that AZD2184 and thioflavin T are able to bind to several sites of the Aβ(1-42) fibril. Due to the small size, planarity and neutrality of AZD2184, it binds more strongly with Aβ(1-42) fibril at all sites. By contrast, thioflavin T has more significant conformational changes after binding, which is the reason that thioflavin T can be used as a fluorescent probe in in vitro studies.In Paper IV, we studied the binding profile of PtdIns(3,4,5)P3 with the plecsktrin homology (PH) domain of Saprolegnia monoica cellulose synthase. We first studied the binding modes of the inositol groups with the PH domain in solution, the results of which were then used to guide the modeling of the binding mode of PtdIns(3,4,5)P3 in a membrane with the PH domain.
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| 5. |
- Guanglin, Kuang, et al.
(författare)
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Theoretical study of the binding profile of an allosteric modulator NS-1738 with a chimera structure of the alpha 7 nicotinic acetylcholine receptor
- 2016
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 18:40, s. 28003-28009
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Tidskriftsartikel (refereegranskat)abstract
- Potentiation of the function of the alpha 7 nicotinic acetylcholine receptor (alpha 7-nAChR) is believed to provide a possible way for the treatment of cholinergic system dysfunctions such as Alzheimer's disease and schizophrenia. Positive allosteric modulators (PAMs) are able to augment the peak current response of the endogenous agonist of alpha 7-nAChR by binding to some allosteric sites. In this study, the binding profile of a potent type I PAM, NS-1738, with a chimera structure (termed alpha 7-AChBP) constructed from the extracellular domain of alpha 7-nAChR and an acetylcholine binding protein was investigated with molecular docking, molecular dynamics simulation, and free energy calculation methods. We found that NS-1738 could bind to three allosteric sites of alpha 7-AChBP, namely, the top pocket, the vestibule pocket and the agonist sub-pocket. NS-1738 has moderate binding affinities (-6.76 to -9.15 kcal mol(-1)) at each allosteric site. The urea group is critical for binding and can form hydrogen-bond interactions with the protein. The bulky trifluoromethyl group also has a great impact on the binding modes and binding affinities. We believe that our study provides valuable insight into the binding profiles of type I PAMs with alpha 7-nAChR and is helpful for the development of novel PAMs.
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| 6. |
- Hussain, M., et al.
(författare)
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ATAD2 in cancer : a pharmacologically challenging but tractable target
- 2018
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Ingår i: Expert opinion on therapeutic targets. - : Taylor and Francis Ltd. - 1472-8222 .- 1744-7631. ; 22:1, s. 85-96
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: ATAD2 protein is an emerging oncogene that has strongly been linked to the etiology of multiple advanced human cancers. Therapeutically, despite the fact that genetic suppression/knockdown studies have validated it as a compelling drug target for future therapeutic development, recent druggability assessment data suggest that direct targeting of ATAD2’s bromodomain (BRD) may be a very challenging task. ATAD2’s BRD has been predicted as a ‘difficult to drug’ or ‘least druggable’ target due to the concern that its binding pocket, and the areas around it, seem to be unfeasible for ligand binding. Areas covered: In this review, after shedding light on the multifaceted roles of ATAD2 in normal physiology as well as in cancer-etiology, we discuss technical challenges rendered by ATAD2’s BRD active site and the recent drug discovery efforts to find small molecule inhibitors against it. Expert opinion: The identification of a novel low-nanomolar semi-permeable chemical probe against ATAD2’s BRD by recent drug discovery campaign has demonstrated it to be a pharmacologically tractable target. Nevertheless, the development of high quality bioavailable inhibitors against ATAD2 is still a pending task. Moreover, ATAD2 may also potentially be utilized as a promising target for future development of RNAi-based therapy to treat cancers.
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| 7. |
- Kuang, Guanglin, et al.
(författare)
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Characterization of the binding mode of the PET tracer [18F]ASEM to a chimera structure of the α7 nicotinic acetylcholine receptor
- 2017
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Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 7:32, s. 19787-19793
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Tidskriftsartikel (refereegranskat)abstract
- The α7 nicotinic acetylcholine receptor (α7-nAChR) is assumed to be implicated in a variety of neurological disorders, such as schizophrenia and Alzheimer's disease (AD). The progress of these disorders can be studied through imaging α7-nAChR with positron emission tomography (PET). [18F]ASEM is a novel and potent α7-nAChR PET radioligand showing great promise in recent tests. However, the mechanism of the molecular interaction between [18F]ASEM and α7-nAChR is still unclear. In this paper, the binding profile of [18F]ASEM to a chimera structure of α7-nAChR was investigated with molecular docking, molecular dynamics, and metadynamics simulation methods. We found that [18F]ASEM binds at the same site as the crystallized agonist epibatidine but with a different binding mode. The dibenzo[b,d]thiophene ring has a different orientation compared to the pyridine ring of epibatidine and has van der Waals interactions with residues from loop C on one side and π-π stacking interaction with Trp53 on the other side. The conformation of Trp53 was found to have a great impact on the binding of [18F]ASEM. Six binding modes in terms of the side chain dihedral angles χ1 and χ2 of Trp53 were discovered by metadynamics simulation. In the most stable binding mode, Trp53 adopts a different conformation from that in the crystalline structure and has a rather favorable π-π stacking interaction with [18F]ASEM. We believe that these discoveries can be valuable for the development of novel PET radioligands.
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| 8. |
- Kuang, Guanglin, et al.
(författare)
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Computational studies of the binding profile of phosphoinositide PtdIns (3,4,5) P-3 with the pleckstrin homology domain of an oomycete cellulose synthase
- 2016
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Saprolegnia monoica is a model organism to investigate Saprolegnia parasitica, an important oomycete which causes considerable loss in aquaculture every year. S. monoica contains cellulose synthases vital for oomycete growth. However, the molecular mechanism of the cellulose biosynthesis process in the oomycete growth is still poorly understood. Some cellulose synthases of S. monoica, such as SmCesA2, are found to contain a plecsktrin homology (PH) domain, which is a protein module widely found in nature and known to bind to phosphoinositides, a class of signaling compounds involved in many biological processes. Understanding the molecular interactions between the PH domain and phosphoinositides would help to unravel the cellulose biosynthesis process of oomycetes. In this work, the binding profile of PtdIns (3,4,5) P-3, a typical phosphoinositide, with SmCesA2-PH was studied by molecular docking, molecular dynamics and metadynamics simulations. PtdIns (3,4,5) P-3 is found to bind at a specific site located at beta 1, beta 2 and beta 1-beta 2 loop of SmCesA2-PH. The high affinity of PtdIns (3,4,5) P-3 to SmCesA2-PH is contributed by the free phosphate groups, which have electrostatic and hydrogenbond interactions with Lys88, Lys100 and Arg102 in the binding site.
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| 9. |
- Kuang, Guanglin, et al.
(författare)
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Insight into the adsorption profiles of the Saprolegnia monoica chitin synthase MIT domain on POPA and POPC membranes by molecular dynamics simulation studies
- 2016
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 18:7, s. 5281-5290
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Tidskriftsartikel (refereegranskat)abstract
- The critical role of chitin synthases in oomycete hyphal tip growth has been established. A microtubule interacting and trafficking (MIT) domain was discovered in the chitin synthases of the oomycete model organism, Saprolegnia monoica. MIT domains have been identified in diverse proteins and may play a role in intracellular trafficking. The structure of the Saprolegnia monoica chitin synthase 1 (SmChs1) MIT domain has been recently determined by our group. However, although our in vitro assay identified increased strength in interactions between the MIT domain and phosphatidic acid (PA) relative to other phospholipids including phosphatidylcholine (PC), the mechanism used by the MIT domain remains unknown. In this work, the adsorption behavior of the SmChs1 MIT domain on POPA and POPC membranes was systematically investigated by molecular dynamics simulations. Our results indicate that the MIT domain can adsorb onto the tested membranes in varying orientations. Interestingly, due to the specific interactions between MIT residues and lipid molecules, the binding affinity to the POPA membrane is much higher than that to the POPC membrane. A binding hotspot, which is critical for the adsorption of the MIT domain onto the POPA membrane, was also identified. The lower binding affinity to the POPC membrane can be attributed to the self-saturated membrane surface, which is unfavorable for hydrogen-bond and electrostatic interactions. The present study provides insight into the adsorption profile of SmChs1 and additionally has the potential to improve our understanding of other proteins containing MIT domains.
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| 10. |
- Kuang, Guanglin, et al.
(författare)
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Investigation of the Binding Profiles of AZD2184 and Thioflavin T with Amyloid-beta(1-42) Fibril by Molecular Docking and Molecular Dynamics Methods
- 2015
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 119:35, s. 11560-11567
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Tidskriftsartikel (refereegranskat)abstract
- Detecting deposits of amyloid beta fibrils in the brain is of paramount importance for an early diagnosis of Alzheimer's disease. A number of PET tracers have been developed for amyloid imaging, but many suffer from poor specificity and large signal to background ratio. Design of tracers with specificity and improved binding affinity requires knowledge about various potential binding sites in the amyloid beta fibril available for the tracers and the nature of the local microenvironment of these sites. In this study we investigate the local structure of fibrils using two important probes, namely, thioflavin T (a fluorescent probe) and AZD2184 (a PET tracer). The target structures for amyloid-beta(1-42) fibril are based on reported NMR solution models. By explicitly considering the effect of fibril flexibility on the available binding sites for all these models, the binding affinity of these probes has been investigated. The binding profiles of AZD2184 and thioflavin T were studied by molecular docking and molecular dynamics simulation methods. The two compounds were found to bind at the same sites of the fibril: three of which are within the fibril, and one is on the two sides of the Met35 residue on the surface. The binding affinity of AZD2184 and thioflavin T is found to be higher at the core sites than on the surface due to more contact residues. The binding affinity of AZD2184 is much higher than that of thioflavin T at every site due to electrostatic interaction and spatial restriction, which is in good agreement with experimental observation. However, the structural change of thioflavin T is much more significant than that of AZD2184, which is the chemical basis for its usage as a fluorescent probe. The ramifications of these results for the design and optimization of PET radioligands and fluorescent probes are briefly discussed.
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| 11. |
- Li, Junhao, et al.
(författare)
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Computational Insight Into Vitamin K-1 omega-Hydroxylation by Cytochrome P450 4F2
- 2018
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Ingår i: Frontiers in Pharmacology. - : Frontiers Media S.A.. - 1663-9812. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Vitamin K-1 (VK1) plays an important role in the modulation of bleeding disorders. It has been reported that omega-hydroxylation on the VK1 aliphatic chain is catalyzed by cytochrome P450 4F2 (CYP4F2), an enzyme responsible for the metabolism of eicosanoids. However, the mechanism of VK1 omega-hydroxylation by CYP4F2 has not been disclosed. In this study, we employed a combination of quantum mechanism (QM) calculations, homology modeling, molecular docking, molecular dynamics (MD) simulations, and combined quantum mechanism/molecular mechanism (QM/MM) calculations to investigate the metabolism profile of VK1 omega-hydroxylation. QM calculations based on the truncated VK1 model show that the energy barrier for omega-hydroxylation is about 6-25 kJ/mol higher than those at other potential sites of metabolism. However, results from the MD simulations indicate that hydroxylation at the omega-site is more favorable than at the other potential sites, which is in accordance with the experimental observation. The evaluation of MD simulations was further endorsed by the QM/MM calculation results. Our studies thus suggest that the active site residues of CYP4F2 play a determinant role in the omega-hydroxylation. Our results provide structural insights into the mechanism of VK1 omega-hydroxylation by CYP4F2 at the atomistic level and are helpful not only for characterizing the CYP4F2 functions but also for looking into the omega-hydroxylation mediated by other CYP4 enzymes.
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| 12. |
- Li, S., et al.
(författare)
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Cholesterol-directed nanoparticle assemblies based on single amino acid peptide mutations activate cellular uptake and decrease tumor volume
- 2017
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Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 8:11, s. 7552-7559
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Tidskriftsartikel (refereegranskat)abstract
- Peptide drugs have been difficult to translate into effective therapies due to their low in vivo stability. Here, we report a strategy to develop peptide-based therapeutic nanoparticles by screening a peptide library differing by single-site amino acid mutations of lysine-modified cholesterol. Certain cholesterol-modified peptides are found to promote and stabilize peptide α-helix formation, resulting in selectively cell-permeable peptides. One cholesterol-modified peptide self-assembles into stable nanoparticles with considerable α-helix propensity stabilized by intermolecular van der Waals interactions between inter-peptide cholesterol molecules, and shows 68.3% stability after incubation with serum for 16 h. The nanoparticles in turn interact with cell membrane cholesterols that are disproportionately present in cancer cell membranes, inducing lipid raft-mediated endocytosis and cancer cell death. Our results introduce a strategy to identify peptide nanoparticles that can effectively reduce tumor volumes when administered to in in vivo mice models. Our results also provide a simple platform for developing peptide-based anticancer drugs.
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| 13. |
- Sun, Lu, et al.
(författare)
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Origin of Ion Selectivity at the Air/Water Interface
- 2015
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 17:6, s. 4311-4318
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Tidskriftsartikel (refereegranskat)abstract
- Among many characteristics of ions, their capability to accumulate at air/water interfaces is a particular issue that has been the subject of much research attention. For example, the accumulation of halide anions (Cl-, Br-, I-) at the water surface is of great importance to heterogeneous reactions that are of environmental concern. However, the actual mechanism that drives anions towards the air/water interface remains unclear. In this work, we have performed atomistic simulations using polarizable models to mimic ionic behavior under atmospheric conditions. We find that larger anions are abundant at the water surface and that the cations are pulled closer to the surface by the counterions. We propose that polarization effects stabilize the anions with large radii when approaching the surface. This energetically more favorable situation is caused by the fact that the more polarized anions at the surface attract water molecules more strongly. Of relevance is also the ordering of the surface water molecules with their hydrogen atoms pointing outwards which induce an external electronic field that leads to a different surface behavior of anions and cations. The water-water interaction is weakened by the distinct water-ion attraction, a point contradicting the proposition that F- is a kosmotrope. The simulation results thus allow us to obtain a more holistic understanding of the interfacial properties of ionic solutions and atmospheric aerosols.
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| 14. |
- Sun, Xianqiang, et al.
(författare)
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Propagation of the Allosteric Modulation Induced by Sodium in the delta-Opioid Receptor
- 2017
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Ingår i: Chemistry - A European Journal. - : John Wiley & Sons. - 0947-6539 .- 1521-3765. ; 23:19, s. 4615-4624
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Tidskriftsartikel (refereegranskat)abstract
- Allosteric sodium in the helix bundle of a G protein-coupled receptor (GPCR) can modulate the receptor activation on the intracellular side. This phenomenon has confounded the GPCR community for decades. In this work, we present a theoretical model that reveals the mechanism of the allosteric modulation induced by sodium in the delta-opioid receptor. We found that the allosteric sodium ion exploits a distinct conformation of the key residue Trp2746.48 to propagate the modulation to helices 5 and 6, which further transmits along the helices and regulates their positions on the intracellular side. This mechanism is supported by subsequent functional assays. Remarkably, our results highlight the contrast between the allosteric effects towards two GPCR partners, the G protein and b-arrestin, as indicated by the fact that the allosteric modulation initiated by the sodium ion significantly affects the b-arrestin recruitment, while it alters the G protein signaling only moderately. We believe that the mechanism revealed in this work can be used to explain allosteric effects initiated by sodium in other GPCRs since the allosteric sodium is highly conserved across GPCRs.
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| 15. |
- Sun, Xianqiang, et al.
(författare)
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Residues remote from the binding pocket control the antagonist selectivity towards the corticotropin-releasing factor receptor-1
- 2015
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5, s. 8066-
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Tidskriftsartikel (refereegranskat)abstract
- The corticotropin releasing factors receptor-1 and receptor-2 (CRF1R and CRF2R) are therapeutic targets for treating neurological diseases. Antagonists targeting CRF1R have been developed for the potential treatment of anxiety disorders and alcohol addiction. It has been found that antagonists targeting CRF1R always show high selectivity, although CRF1R and CRF2R share a very high rate of sequence identity. This has inspired us to study the origin of the selectivity of the antagonists. We have therefore built a homology model for CRF2R and carried out unbiased molecular dynamics and well-tempered metadynamics simulations for systems with the antagonist CP-376395 in CRF1R or CRF2R to address this issue. We found that the side chain of Tyr(6.63) forms a hydrogen bond with the residue remote from the binding pocket, which allows Tyr(6.63) to adopt different conformations in the two receptors and results in the presence or absence of a bottleneck controlling the antagonist binding to or dissociation from the receptors. The rotameric switch of the side chain of Tyr356(6.63) allows the breaking down of the bottleneck and is a perquisite for the dissociation of CP-376395 from CRF1R.
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| 16. |
- Sun, Xianqiang
(författare)
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Theoretical Studies of G-Protein-Coupled Receptors
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The family of G-protein-coupled receptors (GPCRs) contains the largest number of drug targets in the human body, with more than a quarter of the clinically used drugs targeting them. Because of the important roles GPCRs play in the human body, the mechanisms of activation of GPCRs or ligands binding to GPCRs have captivated much research interest since the discovery of GPCRs. A number of GPCR crystal structures determined in recent years have provided us with unprecedented opportunities in investigating how GPCRs function through the conformational changes regulated by their ligands. This has motivated me to perform molecular dynamics (MD) simulations in combination with a variety of other modeling methods to study the activation of some GPCRs and their ligand selectivity.This thesis consists of six chapters. In the first chapter, a brief introduction of GPCRs and MD simulation techniques is given. Detailed MD simulation techniques, including pressure controlling methods and temperature coupling approaches, are described in chapter 2. The metadynamics simulation technique, used to enhance conformational sampling, is described in chapter 3. In chapter 4, I outline the inhomogeneous fluid theory used to calculate the thermodynamics properties of interfacial water molecules. Using the methods described in chapters 2-4, I carried out theoretical investigations on some GPCRs with the results summarized in chapter 5. In chapter 6, I provide a summary of the thesis with future work outlined in an outlook.
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| 17. |
- Wang, Xu, et al.
(författare)
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A theoretical study on the molecular determinants of the affibody protein ZAbeta3 bound to an amyloid beta peptide.
- 2015
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 17:26, s. 16886-16893
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Tidskriftsartikel (refereegranskat)abstract
- Amyloid beta (A beta) peptides are small cleavage products of the amyloid precursor protein. Aggregates of A beta peptides are thought to be linked with Alzheimer's and other neurodegenerative diseases. Strategies aimed at inhibiting amyloid formation and promoting A beta clearance have been proposed and investigated in in vitro experiments and in vivo therapies. A recent study indicated that a novel affibody protein Z(A beta 3), which binds to an A beta 40 monomer with a binding affinity of 17 nM, is able to prevent the aggregation of A beta 40. However, little is known about the energetic contribution of each residue in Z(A beta 3) to the formation of the (Z(A beta 3))(2):A beta complex. To address this issue, we carried out unbiased molecular dynamics simulations and molecular mechanics Poisson-Boltzmann surface area calculations. Through the per-residue decomposition scheme, we identified that the van der Waals interactions between the hydrophobic residues of (Z(A beta 3))(2) and those at the exterior and interior faces of A beta are the main contributors to the binding of (Z(A beta 3))(2) to A beta. Computational alanine scanning identified 5 hot spots, all residing in the binding interface and contributing to the binding of (Z(A beta 3))(2) to A beta through the hydrophobic effect. In addition, the amide hydrogen bonds in the 4-strand beta-sheet and the pi-pi stacking were also analyzed. Overall, our study provides a theoretical basis for future experimental improvement of the Z(A beta 3) peptide binding to A beta.
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| 18. |
- Wang, Xu
(författare)
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Computational Studies of Structures and Binding Properties of Protein-Ligand Complexes
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Proteins are dynamic structural entities that are involved in many biophysical processes through molecular interactions with their ligands. Protein-ligand interactions are of fundamental importance for computer-aided drug discovery. Due to the fast development in computer technologies and theoretical methods, computational studies are by now able to provide atomistic-level description of structures, thermodynamic and dynamic properties of protein-ligand systems, and are becoming indispensable in understanding complicated biomolecular systems. In this dissertation, I have applied molecular dynamic (MD) simulations combined with several state of the art free-energy calculation methodologies, to understand structures and binding properties of several protein-ligand systems.The dissertation consists of six chapters. In the first chapter, I present a brief introduction to classical MD simulations, to recently developed methods for binding free energy calculations, and to enhanced sampling of configuration space of biological systems. The basic features, including the Hamiltonian equations, force fields, integrators, thermostats, and barostats, that contribute to a complete MD simulation are described in chapter 2. In chapter 3, two classes of commonly used algorithms for estimating binding free energies are presented. I highlight enhanced sampling approaches in chapter 4, with a special focus on replica exchange MD simulations and metadynamics, as both of them have been utilized in my work presented in the chapter thereafter. In chapter 5, I outlined the work in the 5 papers included in the thesis. In paper I and II, I applied, respectively, the molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) and alchemical free energy calculation methods to identify the molecular determinant of the affibody protein ZAb3 bound to an amyloid b peptide, and to investigate the binding profile of the positive allosteric modulator NS-1738 with the α7 acetylcholine-binding protein (α7-AChBP protein); in paper III and VI, unbiased MD simulations were integrated with the well-tempered metadynamics approach, with the aim to reveal the mechanism behind the higher selectivity of an antagonist towards corticotropin-releasing factor receptor-1 (CRF1R) than towards CRF2R, and to understand how the allosteric modulation induced by a sodium ion is propagated to the intracellular side of the d-opioid receptor; in the last paper, I proved the structural heterogeneity of the intrinsically disordered AICD peptide, and then employed the bias-exchange metadynamics and kinetic Monte Carlo techniques to understand the coupled folding and binding of AICD to its receptor Fe65-PTB2. I finally proposed that the interactions between AICD and Fe65-PTB2 take place through an induced-fit mechanism. In chapter 6, I made a short conclusion of the work, with an outlook of computational simulations of biomolecular systems.
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| 19. |
- Wang, Yan, et al.
(författare)
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Molecular Adhesion at Clay Nanocomposite Interfaces Depends on Counterion Hydration-Molecular Dynamics Simulation of Montmorillonite/Xyloglucan
- 2015
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 16:1, s. 257-265
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Tidskriftsartikel (refereegranskat)abstract
- Nacre-mimetic clay/polymer nanocomposites with clay platelet orientation parallel to the film surface show interesting gas barrier and mechanical properties. In moist conditions, interfacial adhesion is lowered and mechanical properties are reduced. Molecular dynamic simulations (MD) have been performed to investigate the effects of counterions on molecular adhesion at montmorillonite clay (Mnt)-xyloglucan (XG) interfaces. We focus on the role of monovalent cations K+, Na+, and Li+ and the divalent cation Ca2+ for mediating and stabilizing the Mnt/XG complex formation. The conformation of adsorbed XG is strongly influenced by the choice of counterion and so is the simulated work of adhesion. Free energy profiles that are used to estimate molecular adhesion show stronger interaction between XG and clay in the monovalent cation system than in divalent cation system, following a decreasing order of K-Mnt, Na-Mnt, Li-Mnt, and Ca-Mnt. The Mnt clay hydrates differently in the presence of different counterions, leading to a chemical potential of water that is highest in the case of K-Mnt, followed by Na-Mnt and Li-Mnt, and lowest in the case of Ca-Mnt. This means that water is most easily displaced from the interface in the case of K-Mnt, which contributes to the relatively high work of adhesion. In all systems, the penalty of replacing polymer with water at the interface gives a positive contribution to the work of adhesion of between 19 and 35%. Our work confirms the important role of counterions in mediating the adsorption of biopolymer XG to Mnt clays and predicts potassium or sodium as the best choice of counterions for a Mnt-based biocomposite design.
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| 20. |
- Wang, Yan, et al.
(författare)
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Molecular mechanisms for the adhesion of chitin and chitosan to montmorillonite clay
- 2015
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Ingår i: RSC Advances. - : RSC Publishing. - 2046-2069. ; 5:67, s. 54580-54588
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics simulations have been performed to investigate molecular adhesion of chitin and chitosan oligomers to montmorillonite (Mnt) clay at different degrees of acetylation (DA, 0%, 20%, 40%, 60%, 80% and 100%) and different degree of protonation (DPr, 0%, 50%, 100% mimicking pH > 6.5, pH = 6.5, pH < 4, respectively) under fully hydrated conditions. Although the Mnt surface is negatively charged and a variation in DA also implies going from a positively charged oligomer at DA = 0% to a neutral oligomer at DA = 100%, the simulations show unexpectedly small variation of the total molecular adhesion as a function of DA. From our analysis we propose that this quantitatively similar adhesion arises from two different mechanisms. At low DA, the oligomer is rich in positively charged amino groups interacting strongly with the negatively charged surface by direct electrostatic interaction. On the other hand, at high DA, electrically neutral acetyl groups are strongly correlated with the Na+ counter ions, which are in all cases stuck at the surface and the counter ions seem to act as 'glue' between the acetyl groups and the Mnt. However, when protonation was decreased, adhesion was affected and significantly lowered at neutral conditions (DPr = 0%). The reason is concluded to be differences in charge distributions of the respective functional groups. A further investigation on the intramolecular hydrogen bonds formed in CHT or CHS shows that the adsorbed conformation of the polymer is also highly affected by DA. This work provides fundamental insights into adhesion mechanisms and is of potential importance for the development of polymer-clay based composite materials.
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| 21. |
- Wang, Yan, et al.
(författare)
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Swelling and dimensional stability of xyloglucan/montmorillonite nanocomposites in moist conditions from molecular dynamics simulations
- 2017
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Ingår i: Computational Materials Science. - : Elsevier. - 0927-0256. ; 128, s. 191-197
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Tidskriftsartikel (refereegranskat)abstract
- Nacre-mimetic biocomposites made from the combination of montmorillonite clay and the hemicellulose xyloglucan give materials that retain much of their material properties even at high relative humidity. Here, a model composite system consisting of two clay platelets intercalated by xyloglucan oligomers was studied at different levels of hydration using molecular dynamics simulations, and compared to the pure clay. It was found that xyloglucan inhibits swelling of the clay at low water contents by promoting the formation of nano-sized voids that fill with water without affecting the material's dimensions. At higher water contents the XG itself swells, but at the same time maintaining contact with both platelets across the gallery, thereby acting as a physical cross-linker in a manner similar to the role of XG in the plant cell wall.
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| 22. |
- Wang, Z., et al.
(författare)
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Organelle-Specific Triggered Release of Immunostimulatory Oligonucleotides from Intrinsically Coordinated DNA-Metal-Organic Frameworks with Soluble Exoskeleton
- 2017
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society. - 0002-7863 .- 1520-5126. ; 139:44, s. 15784-15791
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Tidskriftsartikel (refereegranskat)abstract
- DNA has proven of high utility to modulate the surface functionality of metal-organic frameworks (MOFs) for various biomedical applications. Nevertheless, current methods for preparing DNA-MOF nanoparticles rely on either inefficient covalent conjugation or specific modification of oligonucleotides. In this work, we report that unmodified oligonucleotides can be loaded on MOFs with high density (∼2500 strands/particle) via intrinsic, multivalent coordination between DNA backbone phosphate and unsaturated zirconium sites on MOFs. More significantly, surface-bound DNA can be efficiently released in either bulk solution or specific organelles in live cells when free phosphate ions are present. As a proof-of-concept for using this novel type of DNA-MOFs in immunotherapy, we prepared a construct of immunostimulatory DNA-MOFs (isMOFs) by intrinsically coordinating cytosine-phosphate-guanosine (CpG) oligonucleotides on biocompatible zirconium MOF nanoparticles, which was further armed by a protection shell of calcium phosphate (CaP) exoskeleton. We demonstrated that isMOFs exhibited high cellular uptake, organelle specificity, and spatiotemporal control of Toll-like receptors (TLR)-triggered immune responses. When isMOF reached endolysosomes via microtubule-mediated trafficking, the CaP exoskeleton dissolved in the acidic environment and in situ generated free phosphate ions. As a result, CpG was released from isMOFs and stimulated potent immunostimulation in living macrophage cells. Compared with naked CpG-MOF, isMOFs exhibited 83-fold up-regulation in stimulated secretion of cytokines. We thus expect this isMOF design with soluble CaP exoskeleton and an embedded sequential "protect-release" program provides a highly generic approach for intracellular delivery of therapeutic nucleic acids.
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| 23. |
- Zhao, Xin, et al.
(författare)
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Discovery of Highly Potent Pinanamine-Based Inhibitors against Amantadine- and Oseltamivir-Resistant Influenza A Viruses
- 2018
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Ingår i: Journal of Medicinal Chemistry. - : American Chemical Society (ACS). - 0022-2623 .- 1520-4804. ; 61:12, s. 5187-5198
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Tidskriftsartikel (refereegranskat)abstract
- Influenza pandemic is a constant major threat to public health caused by influenza A viruses (IAVs). IAVs are subcategorized by the surface proteins hemagglutinin (HA) and neuraminidase (NA), in which they are both essential targets for drug discovery. While it is of great concern that NA inhibitor oseltamivir resistant strains are frequently identified from human or avian influenza virus, structural and functional characterization of influenza HA has raised hopes for new antiviral therapies. In this study, we explored a structure-activity relationship (SAR) of pinanamine-based antivirals and discovered a potent inhibitor M090 against amantadine-resistant viruses, including the 2009 H1N1 pandemic strains, and oseltamivir-resistant viruses. Mechanism of action studies, particularly hemolysis inhibition, indicated that M090 targets influenza HA and it occupied a highly conserved pocket of the HA(2) domain and inhibited virus-mediated membrane fusion by "locking" the bending state of HA(2) during the conformational rearrangement process. This work provides new binding sites within the HA protein and indicates that this pocket may be a promising target for broad-spectrum anti-influenza A drug design and development.
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| 24. |
- Zhou, Yang, 1986-, et al.
(författare)
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Enhanced Sampling Simulations of Ligand Unbinding Kinetics Controlled by Protein Conformational Changes
- 2019
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Ingår i: Journal of Chemical Information and Modeling. - : AMER CHEMICAL SOC. - 1549-9596 .- 1549-960X. ; 59:9, s. 3910-3918
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Tidskriftsartikel (refereegranskat)abstract
- Understanding unbinding kinetics of protein-ligand systems is of great importance for the design of ligands with desired specificity and safety. In recent years, enhanced sampling techniques have emerged as effective tools for studying unbinding kinetics of protein-ligand systems at the atomistic level. However, in many protein-ligand systems, the ligand unbinding processes are strongly coupled to protein conformational changes and the disclosure of the hidden degrees of freedom closely related to the protein conformational changes so that sampling is enhanced over these degrees of freedom remains a great challenge. Here, we show how potential-scaled molecular dynamics (sMD) and infrequent metadynamics (InMetaD) simulation techniques can be combined to successfully reveal the unbinding mechanism of 3-(1,4-diazabicyclo[3.2.2]nonan-4-yl)-6-[F-18]fluorodibenzo[b,d]thiophen e 5,5-dioxide ([F-18]ASEM) from a chimera structure of the alpha 7-nicotinic acetylcholine receptor. By using sMD simulations, we disclosed that the "close to "open" conformational change of loop C plays a key role in the ASEM unbinding process. By carrying out InMetaD simulations with this conformational change taken into account as an additional collective variable, we further captured the key states in the unbinding process and clarified the unbinding mechanism of ASEM from the protein. Our work indicates that combining sMD and InMetaD simulation techniques can be an effective approach for revealing the unbinding mechanism of a protein-ligand system where protein conformational changes control the unbinding process.
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| 25. |
- Zhou, Yang, 1986-, et al.
(författare)
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Mechanistic insights into peptide and ligand binding of the ATAD2-bromodomain via atomistic simulations disclosing a role of induced fit and conformational selection
- 2018
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 20:36, s. 23222-23232
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Tidskriftsartikel (refereegranskat)abstract
- ATAD2 has emerged as a promising bromodomain (BRD)-containing therapeutic drug target in multiple human cancers. However, recent druggability assessment studies predicted ATAD2's BRD as a target 'difficult to drug' because its binding pocket possesses structural features that are unfeasible for ligand binding. Here, by using all-atom molecular dynamics simulations and an advanced metadynamics method, we demonstrate a dynamic view of the binding pocket features which can hardly be obtained from the "static" crystal data. The most important features disclosed from our simulation data, include: (1) a distinct 'open-to-closed' conformational switch of the ZA loop region in the context of peptide or ligand binding, akin to the induced fit mechanism of molecular recognition, (2) a dynamic equilibrium of the BC loop "in" and "out" conformations, highlighting a role in the conformational selection mechanism for ligand binding, and (3) a new binding region identified distal to the histone-binding pocket that might have implications in bromodomain biology and in inhibitor development. Moreover, based on our simulation results, we propose a model for an "auto-regulatory" mechanism of ATAD2's BRD for histone binding. Overall, the results of this study will not only have implications in bromodomain biology but also provide a theoretical basis for the discovery of new ATAD2's BRD inhibitors.
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| 26. |
- Zou, Rongfeng, et al.
(författare)
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Activity of Antimicrobial Peptide Aggregates Decreases with Increased Cell Membrane Embedding Free Energy Cost
- 2018
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Ingår i: Biochemistry. - : AMER CHEMICAL SOC. - 0006-2960 .- 1520-4995. ; 57:18, s. 2606-2610
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Tidskriftsartikel (refereegranskat)abstract
- Antimicrobial peptides (AMPs) are a promising alternative to antibiotics for mitigating bacterial infections, in light of increasing bacterial resistance to antibiotics. However, predicting, understanding, and controlling the antibacterial activity of AMPs remain a significant challenge. While peptide intramolecular interactions are known to modulate AMP antimicrobial activity, peptide intermolecular interactions remain elusive in their impact on peptide bioactivity. Herein, we test the relationship between AMP intermolecular interactions and antibacterial efficacy by controlling AMP intermolecular hydrophobic and hydrogen bonding interactions. Molecular dynamics simulations and Gibbs free energy calculations in concert with experimental assays show that increasing intermolecular interactions via interpeptide aggregation increases the energy cost for the peptide to embed into the bacterial cell membrane, which in turn decreases the AMP antibacterial activity. Our findings provide a route for predicting and controlling the antibacterial activity of AMPs against Gram-negative bacteria via reductions of intermolecular AMP interactions.
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| 27. |
- Zou, Rongfeng
(författare)
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Computational Studies of Protein-ligand Systems Using Enhanced Sampling Methods
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on studies of protein-ligand systems using enhanced sampling methods. In chapter I, I give a brief introduction to the time-scale problem and some enhanced sampling methods. In chapter II, the basics of MD simulation are reviewed. In chapter III, the theoretical backgrounds of umbrella sampling, bias-exchange metadynamics and infrequent metadynamics are presented. In chapter IV, the 5 papers included in this thesis are summarized. In paper 1, we studied the relationship between the antibacterial activities of antimicrobial peptides and their aggregation propensities. We found that an increasing aggregation propensity increases the free energy cost of peptide embedding into the bacterial membrane and decreases antibacterial activity. In paper 2, we employed the umbrella sampling approach to obtain the free energy landscape of Pittsburgh compound-B penetrating into the core binding sites of amyloid βfibrils. Our study suggested that, for the design of probes binding to fibril like proteins, other than the binding affinity, the dynamics of probes in the fibrils should also be considered. In paper 3, we studied the coupled folding and binding process of the intrinsically disordered protein p53 to MDM2 with bias-exchange metadynamics and infrequent metadynamics. We reconstructed the free energy landscape and built a kinetic network for this process. In paper 4, we studied the binding modes of ASEM with a chimera structure of α7 nicotinic acetylcholine receptor with well-tempered metadynamics. We found that an important residue, Trp53, can significantly affect the stabilities of the binding modes. In paper 5, we proposed an efficient method to estimate the transition times of rare events in biomolecular systems. In chapter V, I present a conclusion of this thesis and propose an outlook related to the selection of collective variables for enhanced sampling methods.
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| 28. |
- Zou, Rongfeng, et al.
(författare)
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Free Energy Profile for Penetration of Pittsburgh Compound-B into the Amyloid beta Fibril
- 2019
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Ingår i: ACS Chemical Neuroscience. - : American Chemical Society (ACS). - 1948-7193. ; 10:3, s. 1783-1790
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Tidskriftsartikel (refereegranskat)abstract
- The amyloid beta (A beta) fibril is a hallmark of Alzheimer's disease (AD) and has therefore served as an important target for early diagnosis of AD. The Pittsburgh Compound-B (PiB) is one of the most famous positron emission tomography (PET) tracers commonly used for in vivo detection of A beta fibrils. Many theoretical studies have predicted the existence of various core binding sites with different microenvironments for probes binding to the A beta fibril. However, little attention has been devoted to how the probes actually penetrate into the different core binding sites. In this study, an integrated molecular modeling scheme is used to study the penetration of PiB into the core binding sites of the A beta(1-42) fibril structure recently obtained by cryogenic electron microscopy. We find that there are two core binding sites for PiB with dramatic differences in cavity size and microenvironment properties, and furthermore that the penetration of PiB into site-1 is energetically prohibitive, whereas the penetration into site 2 is much more favorable. Therefore, the binding capacity at site-2 may be larger than that at site-1 despite its lower binding affinity. Our results thus suggest that site-2 may be a major binding site for PiB binding to A beta fibril and emphasize the importance to adopt a full dynamical picture when studying tracer fibril binding problems in general, something that in turn can be used to guide the development of tracers with higher affinity and selectivity for the A beta fibril.
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