| 1. |
- Benach, J, et al.
(författare)
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Structure of bacterial 3 beta/17 beta-hydroxysteroid dehydrogenase at 1.2 angstrom resolution : A model for multiple steroid recognition
- 2002
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 41:50, s. 14659-14668
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Tidskriftsartikel (refereegranskat)abstract
- The enzyme 3beta/17beta-hydroxysteroid dehydrogenase (3beta/17beta-HSD) is a steroid-inducible component of the Gram-negative bacterium Conramonas testosteroni. It catalyzes the reversible reduction/ dehydrogenation of the oxo/beta-hydroxy groups at positions 3 and 17 of steroid compounds, including hormones and isobile acids. Crystallographic analysis at 1.2 Angstrom resolution reveals the enzyme to have nearly identical subunits that form a tetramer with 222 symmetry. This is one of the largest oligomeric structures refined at this resolution. The subunit consists of a monomer with a single-domain structure built around a seven-stranded beta-sheet flanked by six alpha-helices. The active site contains a Ser-Tyr-Lys triad, typical for short-chain dehydrogenases/reductases (SDR). Despite their highly diverse substrate specificities, SDR members show a close to identical folding pattern architectures and a common catalytic mechanism. In contrast to other SDR apostructures determined, the substrate binding loop is well-defined. Analysis of structure-activity relationships of catalytic cleft residues, docking analysis of substrates and inhibitors, and accessible surface analysis explains how 3beta/17beta-HSD accommodates steroid substrates of different conformations.
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| 2. |
- Filling, C, et al.
(författare)
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Critical residues for structure and catalysis in short-chain dehydrogenases/reductases
- 2002
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 277:28, s. 25677-25684
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Tidskriftsartikel (refereegranskat)abstract
- Short-chain dehydrogenases/reductases form a large, evolutionarily old family of NAD(P)(H)-dependent enzymes with over 60 genes found in the human genome. Despite low levels of sequence identity (often 10-30%), the three-dimensional structures display a highly similar alpha/beta folding pattern. We have analyzed the role of several conserved residues regarding folding, stability, steady-state kinetics, and coenzyme binding using bacterial 3beta/17beta-hydroxysteroid dehydrogenase and selected mutants. Structure determination of the wildtype enzyme at 1.2-Angstrom resolution by x-ray crystallography and docking analysis was used to interpret the biochemical data. Enzyme kinetic data from mutagenetic replacements emphasize the critical role of residues Thr-12, Asp-60, Asn-86, Asn-87, and Ala-88 in coenzyme binding and catalysis. The data also demonstrate essential interactions of Asn-111 with active site residues. A general role of its side chain interactions for maintenance of the active site configuration to build up a proton relay system is proposed. This extends the previously recognized catalytic triad of Ser-Tyr-Lys residues to form a tetrad of Asn-Ser-Tyr-Lys in the majority of characterized short-chain dehydrogenases/reductase enzymes.
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| 3. |
- Filling, C, et al.
(författare)
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Structural role of conserved Asn179 in the short-chain dehydrogenase/reductase scaffold
- 2001
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Ingår i: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier BV. - 0006-291X .- 1090-2104. ; 289:3, s. 712-717
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Tidskriftsartikel (refereegranskat)abstract
- Short-chain dehydrogenases/reductases (SDR) constitute a large family of enzymes found in all forms of life. Despite a low level of sequence identity, the three-dimensional structures determined display a nearly superimposable alpha/beta folding pattern. We identified a conserved asparagine residue located within strand betaF and analyzed its role in the short-chain dehydrogenase/reductase architecture. Mutagenetic replacement of Asn179 by Ala in bacterial 3 beta /17 beta -hydroxysteroid dehydrogenase yields a folded, but enzymatically inactive enzyme, which is significantly more resistant to denaturation by guanidinium hydrochloride. Crystallographic analysis of the wild-type enzyme at 1.2-Angstrom resolution reveals a hydrogen bonding network, including a buried and well-ordered water molecule connecting strands betaE to betaF, a common feature found in 16 of 21 known three-dimensional structures of the family. Based on these results, we hypothesize that in mammalian 11 beta -hydroxysteroid dehydrogenase the essential Asn-linked glycosylation site, which corresponds to the conserved segment, displays similar structural features and has a central role to maintain the SDR scaffold.
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| 4. |
- Foloppe, N, et al.
(författare)
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Structure, dynamics and electrostatics of the active site of glutaredoxin 3 from Escherichia coli : Comparison with functionally related proteins
- 2001
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Ingår i: Journal of Molecular Biology. - : Elsevier BV. - 0022-2836 .- 1089-8638. ; 310:2, s. 449-470
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Tidskriftsartikel (refereegranskat)abstract
- The chemistry of active-site cysteine residues is central to the activity of thiol-disulfide oxidoreductases of the thioredoxin superfamily. In these reactions, a nucleophilic thiolate is required, but the associated pK(a), values differ vastly in the superfamily, from less than 4 in DsbA to greater than 7 in Trx. The factors that stabilize this thiolate are, however, not clearly established. The glutaredoxins (Grxs), which are members of this superfamily, contain a Cys-Pro-Tyr-Cys motif in their active site. In reduced Grxs, the pK(a) of the N-terminal active-site nucleophilic cysteine residue is lowered significantly, and the stabilization of the corresponding thiolate is expected to influence the redox potential of these enzymes. Here, we use a combination of long molecular dynamics (MD) simulations, pK(a) calculations, and experimental investigations to derive the structure and dynamics of the reduced active site from Escherichia coli Grx3, and investigate the factors that stabilize the thiolate. Several different MD simulations converged toward a consensus conformation for the active-site cysteine residues (Cys11 and Cys14), after a number of local conformational changes. Key features of the model were tested experimentally by measurement of NMR scalar coupling constants, and determination of pK(a) values of selected residues. The pK(a) values of the Grx3 active-site residues were calculated during the MD simulations, and support the underlying structural model. The structure of Grx3, in combination with the pK(a) calculations, indicate that the pK(a) of the N-terminal active-site cysteine residue in Grx3 is intermediate between that of its counterpart in DsbA and Trx. The pK(a) values in best agreement with experiment are obtained with a low (<4) protein dielectric constant. The calculated pK(a) values fluctuate significantly in response to protein dynamics, which underscores the importance of the details of the underlying structures when calculating pK(a) values. The thiolate of Cys11 is stabilized primarily by direct hydrogen bonding with the amide protons of Tyr13 and Cys14 and the thiol proton of Cys14, rather than by long range interactions from charged groups or from a helix macrodipole. From the comparison of reduced Grx3 with other members of the thioredoxin superfamily, a unifying theme for the structural basis of thiol pK(a) differences in this superfamily begins to emerge.
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| 5. |
- Hermann, Stefan, et al.
(författare)
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How transcriptional activators bind target proteins
- 2001
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 276:43, s. 40127-40132
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Tidskriftsartikel (refereegranskat)abstract
- The product of the proto-oncogene c-myc influences many cellular processes through the regulation of specific target genes. Through its transactivation domain (TAD), c-Myc protein interacts with several transcription factors, including TATA-binding protein (TBP). We present data that suggest that in contrast to some other transcriptional activators, an extended length of the c-Myc TAD is required for its binding to TBP. Our data also show that this interaction is a multistep process, in which a rapidly forming low affinity complex slowly converts to a more stable form. The initial complex formation results from ionic or polar interactions, whereas the slow conversion to a more stable form is hydrophobic in nature. Based on our results, we suggest two alternative models for activation domain/target protein interactions, which together provide a single universal paradigm for understanding activator-target factor interactions.
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| 6. |
- Holmgren, A, et al.
(författare)
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Glutaredoxin
- 2002
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Ingår i: Encyclopedia of Molecular Biology. - : John Wiley & Sons. - 9780471209188
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 7. |
- Holmgren, A, et al.
(författare)
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Thioredoxin
- 2002
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Ingår i: Encyclopedia of Molecular Biology. - : John Wiley & Sons. - 9780471209188
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Holmgren, A, et al.
(författare)
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Thioredoxin Reductase
- 2002
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Ingår i: Encyclopedia of Molecular Biology. - : John Wiley & Sons. - 9780471209188
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Jimenez, A, et al.
(författare)
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Human spermatid-specific thioredoxin-1 (Sptrx-1) is a two-domain protein with oxidizing activity
- 2002
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Ingår i: FEBS Letters. - 0014-5793 .- 1873-3468. ; 530:1-3, s. 79-84
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Tidskriftsartikel (refereegranskat)abstract
- Spermatid-specific thioredoxin-1 (Sptrx-1) is the first member of the thioredoxin family of proteins with a tissue-specific expression pattern, found exclusively in the tail of elongating spermatids and spermatozoa. We describe here further biochemical characterization of human Sptrx-1 protein structure and enzymatic activity. In gel filtration chromatography human Sptrx-1 eluates as a 400 kDa protein consistent with either an oligomeric form, not maintained by intermolecular disulfide bonding, and/or a highly asymmetrical structure. Analysis of circular dichroism spectra of fragments 1-360 and 361-469 and comparison to spectra of full-length Sptrx-1 supports a two-domain organization with a largely unstructured N-terminal domain and a folded thioredoxin-like C-terminal domain. Functionally, Sptrx-1 behaves as an oxidant in vitro when using selenite, but not oxidized glutathione, as electron acceptor. This oxidizing enzymatic activity suggests that Sptrx-1 might govern the stabilization (by disulfide cross-linking) of the different structures in the developing tail of spermatids and spermatozoa.
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| 10. |
- Lebbink, J H G, et al.
(författare)
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Structural and thermodynamic studies on a salt-bridge triad in the NADP-binding domain of glutamate dehydrogenase from Thermotoga maritima : Cooperativity and electrostatic contribution to stability
- 2002
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 41:52, s. 15524-15535
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Tidskriftsartikel (refereegranskat)abstract
- Cooperative interactions within ion-pair networks of hyperthermostable proteins are thought to be a major determinant for extreme protein stability. While the favorable thermodynamic contributions of optimized electrostatics in general as well as those of pairwise interactions have been documented, cooperativity between pairwise interactions has not yet been studied thermodynamically in proteins from hyperthermophiles. In this study we use the isolated cofactor binding domain of glutamate dehydrogenase from the hyperthermophilic bacterium Thermotoga maritima to analyze pairwise and cooperative interactions within the salt-bridge triad Arg190-Glu231-Lys193. The X-ray structure of the domain was solved at 1.43 Angstrom and reveals the salt-bridge network with surrounding solvent molecules in detail. All three participating charges in the network were mutated to alanine in all combinations. The X-ray structure of the variant lacking all three charges reveals that the removal of the side chains has no effect on the overall conformation of the protein. Using solvent denaturation and thermodynamic cycles, the interaction energies between each pair of residues in the network were determined in the presence and in the absence of the third residue. Both the Arg190-Glu231 ion pair and the Lys193-Glu231 salt bridge in the absence of the third residue, contribute favorably to the free energy for unfolding of the domain in urea. Using guanidinium chloride as denaturant reveals a strong cooperativity between the two ion-pair interactions, the presence of the second ion pair converts the first interaction from destabilizing into stabilizing by as much as 1.09 kcal/mol. The different energetics of the salt-bridge triad in urea and GdmCl are discussed with reference to the observed anion binding in the crystal structure at high ionic strength and their possible role in a highly charged, high-temperature environment such as the cytoplasm of hyperthermophiles.
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