Atomic Resolution Structures of the Core Domain of Avian Sarcoma Virus Integrase and Its D64N Mutant.
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Journal Article↗
Biomedical subjects
Z Dauter
Publications and source records attributed to Z Dauter.
Atomic resolution structures of the core domain of avian sarcoma virus integrase and its D64N mutant.
Six crystal structures of the core domain of integrase (IN) from avian sarcoma virus (ASV) and its active-site derivative containing an Asp64 --> Asn substitution have been solved at atomic resolution ranging 1.02-1.42 A. The high-quality data provide new structural information about the active site of the enzyme and clarify previous inconsistencies in the description of this fragment. The very high resolution of the data and excellent quality of the refined models explain the dynamic properties of IN and the multiple conformations of its disordered residues. They also allow an accurate description of the solvent structure and help to locate other molecules bound to the enzyme. A detailed analysis of the flexible active-site region, in particular the loop formed by residues 144-154, suggests conformational changes which may be associated with substrate binding and enzymatic activity. The pH-dependent conformational changes of the active-site loop correlates with the pH vs activity profile observed for ASV IN.
Amino Acid Substitution↗
Experimental observation of bonding electrons in proteins.
We demonstrate with two examples the success and potential of recent developments in x-ray protein crystallography at ultra high resolution. Our preliminary structural analyses using diffraction data collected for the two proteins crambin and savinase show meaningful deviations from the conventional independent spherical atom approximation. A noise-reduction averaging technique enables bonding details of electron distributions in proteins to be revealed experimentally for the first time. We move one step closer to imaging directly the fine details of the electronic structure on which the biological function of a protein is based.
Animals↗
X-ray structure of Novamyl, the five-domain "maltogenic" alpha-amylase from Bacillus stearothermophilus: maltose and acarbose complexes at 1.7A resolution.
The three-dimensional structure of the Bacillus stearothermophilus "maltogenic" alpha-amylase, Novamyl, has been determined by X-ray crystallography at a resolution of 1.7 A. Unlike conventional alpha-amylases from glycoside hydrolase family 13, Novamyl exhibits the five-domain structure more usually associated with cyclodextrin glycosyltransferase. Complexes of the enzyme with both maltose and the inhibitor acarbose have been characterized. In the maltose complex, two molecules of maltose are found in the -1 to -2 and +2 to +3 subsites of the active site, with two more on the C and E domains. The C-domain maltose occupies a position identical to one previously observed in the Bacillus circulans CGTase structure [Lawson, C. L., et al. (1994) J. Mol. Biol. 236, 590-600], suggesting that the C-domain plays a genuine biological role in saccharide binding. In the acarbose-maltose complex, the tetrasaccharide inhibitor acarbose is found as an extended hexasaccharide species, bound in the -3 to +3 subsites. The transition state mimicking pseudosaccharide is bound in the -1 subsite of the enzyme in a 2H3 half-chair conformation, as expected. The active site of Novamyl lies in an open gully, fully consistent with its ability to perform internal cleavage via an endo as opposed to an exo activity.
Acarbose↗
Can anomalous signal of sulfur become a tool for solving protein crystal structures?
A general method for solving the phase problem from native crystals of macromolecules has long eluded structural biology. For well diffracting crystals this goal can now be achieved, as is shown here, thanks to modern data collection techniques and new statistical phasing algorithms. Using solely a native crystal of tetragonal hen egg-white lysozyme, a protein of 14 kDa molecular mass, it was possible to detect the positions of the ten sulfur and seven chlorine atoms from their anomalous signal, and proceed from there to obtain an electron-density map of very high quality.
Algorithms↗
Anomalous signal of solvent bromides used for phasing of lysozyme.
The anomalous signal of bromide ions, present in the crystal structure of tetragonal hen egg-white lysozyme through the substitution of NaCl by NaBr in the crystallization medium, was used for phasing of X-ray data collected to 1.7 A resolution with a wavelength near the absorption edge of bromine. Phasing of a single wavelength data set, based purely on anomalous deltaf " contribution, led to easily interpretable electron density, equivalent to the complete multiwavelength anonalous dispersion phasing based on four-wavelength data. The classic small-structure direct methods program SHELXS run against all anomalous differences gave a successful solution of six highest peaks corresponding to six bromide ions in the structure with data limited up to a resolution of 3.5 A. Interpretable maps were obtained at a resolution up to 3.0 A using programs MLPHARE and DM. Bromide ions occupy well ordered positions at the protein surface. Phasing based on the single wavelength signal of anomalous scatterers introduced into the ordered solvent shell can be proposed as a tool for solving structures of well diffracting crystals.
Algorithms↗
Crystal structure of dUTPase from equine infectious anaemia virus; active site metal binding in a substrate analogue complex.
The X-ray structures of dUTPase from equine infectious anaemia virus (EIAV) in unliganded and complexed forms have been determined to 1.9 and 2.0 A resolution, respectively. The structures were solved by molecular replacement using Escherichia coli dUTPase as search model. The exploitation of a relatively novel refinement approach for the initial model, combining maximum likelihood refinement with stereochemically unrestrained updating of the model, proved to be of crucial importance and should be of general relevance.EIAV dUTPase is a homotrimer where each subunit folds into a twisted antiparallel beta-barrel with the N and C-terminal portions interacting with adjacent subunits. The C-terminal 14 and 17 amino acid residues are disordered in the crystal structure of the unliganded and complexed enzyme, respectively. Interactions along the 3-fold axis include a water-containing volume (size 207 A3) which has no contact with bulk solvent. It has earlier been shown that a divalent metal ion is essential for catalysis. For the first time, a putative binding site for such a metal ion, in this case Sr2+, is established. The positions of the inhibitor (the non-hydrolysable substrate analogue dUDP) and the metal ion in the complex are consistent with the location of the active centre established for trimeric dUTPase structures, in which subunit interfaces form three surface clefts lined with evolutionary conserved residues. However, a detailed comparison of the active sites of the EIAV and E. coli enzymes reveals some structural differences. The viral enzyme undergoes a small conformational change in the uracil-binding beta-hairpin structure upon dUDP binding not observed in the other known dUTPase structures.
Amino Acid Sequence↗
Catalysis and specificity in enzymatic glycoside hydrolysis: a 2,5B conformation for the glycosyl-enzyme intermediate revealed by the structure of the Bacillus agaradhaerens family 11 xylanase.
BACKGROUND: The enzymatic hydrolysis of glycosides involves the formation and subsequent breakdown of a covalent glycosyl-enzyme intermediate via oxocarbenium-ion-like transition states. The covalent intermediate may be trapped on-enzyme using 2-fluoro-substituted glycosides, which provide details of the intermediate conformation and noncovalent interactions between enzyme and oligosaccharide. Xylanases are important in industrial applications - in the pulp and paper industry, pretreating wood with xylanases decreases the amount of chlorine-containing chemicals used. Xylanases are structurally similar to cellulases but differ in their specificity for xylose-based, versus glucose-based, substrates. RESULTS: The structure of the family 11 xylanase, Xyl11, from Bacillus agaradhaerens has been solved using X-ray crystallography in both native and xylobiosyl-enzyme intermediate forms at 1.78 A and 2.0 A resolution, respectively. The covalent glycosyl-enzyme intermediate has been trapped using a 2-fluoro-2-deoxy substrate with a good leaving group. Unlike covalent intermediate structures for glycoside hydrolases from other families, the covalent glycosyl-enzyme intermediate in family 11 adopts an unusual 2,5B conformation. CONCLUSIONS: The 2,5B conformation found for the alpha-linked xylobiosyl-enzyme intermediate of Xyl11, unlike the 4C1 chair conformation observed for other systems, is consistent with the stereochemical constraints required of the oxocarbenium-ion-like transition state. Comparison of the Xyl11 covalent glycosyl-enzyme intermediate with the equivalent structure for the related family 12 endoglucanase, CelB, from Streptomyces lividans reveals the likely determinants for substrate specificity in this clan of glycoside hydrolases.
Bacillus↗
Penicillin V acylase crystal structure reveals new Ntn-hydrolase family members.
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Bacillus↗
1.7 A structure of the stabilized REIv mutant T39K. Application of local NCS restraints.
The X-ray structure of the T39K mutant of the variable domain of a human immunoglobulin kappa light chain has been determined at room temperature to 1.7 A resolution with a conventional R factor of 0. 182. T39K crystallizes in the triclinic space group P1 [a = 35.4 (1), b = 40.1 (1), c = 43.1 (1) A, alpha = 66.9 (1), beta = 85.4 (1), gamma = 73.8 (1) degrees ]. The unit-cell contains two monomers, related by a non-crystallographic twofold axis. The use of a novel type of local non-crystallographic symmetry restraints on related isotropic displacement parameters and 1-4 distances as incorporated in the refinement program SHELXL improves the model and quality of the maps, but local differences between both monomers in areas subject to different packing contacts can still be observed. 12 overall anisotropic scaling parameters were refined. These may have compensated for the difficulties in accurately scaling single rotation axis image plate data from a triclinic crystal, because of the scarcity of common equivalent reflections. The final model has been used to perform a number of tests on anisotropic scaling, non-crystallographic symmetry, anisotropic refinement, determination of standard uncertainties and bulk solvent correction. It is remarkable that removal of the NCS restraints from the final model caused Rfree to increase. These tests clarify the strategies for optimum use of SHELXL for refinement at medium as opposed to atomic resolution.
Crystallography, X-Ray↗
Crystallization and preliminary diffraction data analysis of both single and pseudo-merohedrally twinned crystals of rubredoxin oxygen oxidoreductase from Desulfovibrio gigas.
Crystals of rubredoxin oxygen oxidoreductase have been obtained and characterized. They belong to space group P2(1)2(1)2, with unit-cell dimensions a = 88.24 (15), b = 101.25 (7), c = 90.80 (3) A. The homodimer (86 kDa) in the asymmetric unit is related by a non-crystallographic twofold rotation axis parallel to the ab 'diagonal' direction, as shown by the self-rotation maximum in the section with chi = 180 degrees. This pseudo-crystallographic symmetry element was also found to be the twinning axis of pseudo-merohedrally twinned crystals, leading to apparent pseudo-tetragonal P42(1)2 crystal symmetry.
Cold Temperature↗
How RhoGDI binds Rho.
Like all Rho (Ras homology) GTPases, RhoA functions as a molecular switch in cell signaling, alternating between GTP- and GDP-bound states, with its biologically inactive GDP-bound form maintained as a cytosolic complex with RhoGDI (guanine nucleotide-exchange inhibitor). The crystal structures of RhoA-GDP and of the C-terminal immunoglobulin-like domain of RhoGDI (residues 67-203) are known, but the mechanism by which the two proteins interact is not known. The functional human RhoA-RhoGDI complex has been expressed in yeast and crystallized (P6(5)22, unit-cell parameters a = b = 139, c = 253 A, two complexes in the asymmetric unit). Although diffraction from these crystals extends to 3.5 A and is highly anisotropic, the experimentally phased (MAD plus MIR) electron-density map was adequate to reveal the mutual disposition of the two molecules. The result was validated by molecular-replacement calculations when data were corrected for anisotropy. Furthermore, the N-terminus of RhoGDI (the region involved in inhibition of nucleotide exchange) can be identified in the electron-density map: it is bound to the switch I and switch II regions of RhoA, occluding an epitope which binds Dbl-like nucleotide-exchange factors. The entrance of the hydrophobic pocket of RhoGDI is 25 A from the last residue in the RhoA model, with its C-terminus oriented to accommodate the geranylgeranyl group without conformational change in RhoA.
Binding Sites↗
Data-collection strategies.
The optimal strategy for collecting X-ray diffraction data from macromolecular crystals is discussed. Two kinds of factors influencing the completeness of data are considered. The first are geometric, arising from the symmetry of the reciprocal lattice and from the experimental setup; they affect quantitatively the completeness of the measured set of reflections. The second concern the quality, or information content, of the recorded intensities of these measured reflections.
Crystallography, X-Ray↗
Crystal structure of human muscle aldolase complexed with fructose 1,6-bisphosphate: mechanistic implications.
Fructose 1,6-bisphosphate aldolase catalyzes the reversible cleavage of fructose 1,6-bisphosphate and fructose 1-phosphate to dihydroxyacetone phosphate and either glyceraldehyde 3-phosphate or glyceraldehyde, respectively. Catalysis involves the formation of a Schiff's base intermediate formed at the epsilon-amino group of Lys229. The existing apo-enzyme structure was refined using the crystallographic free-R-factor and maximum likelihood methods that have been shown to give improved structural results that are less subject to model bias. Crystals were also soaked with the natural substrate (fructose 1,6-bisphosphate), and the crystal structure of this complex has been determined to 2.8 A. The apo structure differs from the previous Brookhaven-deposited structure (1ald) in the flexible C-terminal region. This is also the region where the native and complex structures exhibit differences. The conformational changes between native and complex structure are not large, but the observed complex does not involve the full formation of the Schiff's base intermediate, and suggests a preliminary hydrogen-bonded Michaelis complex before the formation of the covalent complex.
Borohydrides↗
Contribution of a conserved asparagine to the conformational stability of ribonucleases Sa, Ba, and T1.
The contribution of hydrogen bonding by peptide groups to the conformational stability of globular proteins was studied. One of the conserved residues in the microbial ribonuclease (RNase) family is an asparagine at position 39 in RNase Sa, 44 in RNase T1, and 58 in RNase Ba (barnase). The amide group of this asparagine is buried and forms two similar intramolecular hydrogen bonds with a neighboring peptide group to anchor a loop on the surface of all three proteins. Thus, it is a good model for the hydrogen bonding of peptide groups. When the conserved asparagine is replaced with alanine, the decrease in the stability of the mutant proteins is 2.2 (Sa), 1.8 (T1), and 2.7 (Ba) kcal/mol. When the conserved asparagine is replaced by aspartate, the stability of the mutant proteins decreases by 1.5 and 1.8 kcal/mol for RNases Sa and T1, respectively, but increases by 0.5 kcal/mol for RNase Ba. When the conserved asparagine was replaced by serine, the stability of the mutant proteins was decreased by 2.3 and 1.7 kcal/mol for RNases Sa and T1, respectively. The structure of the Asn 39 --> Ser mutant of RNase Sa was determined at 1.7 A resolution. There is a significant conformational change near the site of the mutation: (1) the side chain of Ser 39 is oriented differently than that of Asn 39 and forms hydrogen bonds with two conserved water molecules; (2) the peptide bond of Ser 42 changes conformation in the mutant so that the side chain forms three new intramolecular hydrogen bonds with the backbone to replace three hydrogen bonds to water molecules present in the wild-type structure; and (3) the loss of the anchoring hydrogen bonds makes the surface loop more flexible in the mutant than it is in wild-type RNase Sa. The results show that burial and hydrogen bonding of the conserved asparagine make a large contribution to microbial RNase stability and emphasize the importance of structural information in interpreting stability studies of mutant proteins.
Asparagine↗
Structural parameters for proteins derived from the atomic resolution (1.09 A) structure of a designed variant of the ColE1 ROP protein.
The crystal structure of a designed variant of the ColE1 repressor of primer (ROP) protein has been refined with SHELXL93 to a resolution of 1.09 A. The final model with 510 non-H protein atoms, 576 H atoms in calculated positions and 114 water molecules converged to a standard R factor of 10% using unrestrained blocked full-matrix refinement. For all non-H atoms six-parameter anisotropic thermal parameters have been refined. The majority of atomic vibrations have a preferred orientation which is approximately perpendicular to the bundle axis; analysis with the TLS method [Schomaker & Trueblood (1968). Acta Cryst. B24, 63-77] showed a relatively good agreement between the individual atomic displacements and a rigid-body motion of the protein. Disordered residues with multiple conformations form clusters on the surface of the protein; six C-terminal residues have been omitted from the refined model due to disorder. Part of the solvent structure forms pentagonal or hexagonal clusters which bridge neighbouring protein molecules. Some water molecules are also conserved in wild-type ROP. The unrestrained blocked full-matrix least-squares refinement yielded reliable estimates of the standard deviations of the refined parameters. Comparison of these parameters with the stereochemical restraints used in various protein refinement programs showed statistically significant differences. These restraints should be adapted to the refinement of macromolecules by taking into account parameters determined from atomic resolution protein structures.
Anisotropy↗
The refined structure of dUTPase from Escherichia coli.
Deoxyuridine 5'-triphosphate nucleotidohydrolase (dUTPase, E.C. 3.6. 1.23) catalyzes the hydrolysis of dUTP to dUMP and pyrophosphate and is involved in nucleotide metabolism and DNA synthesis. A crystal of the recombinant E. coli enzyme, precipitated from polyethylene glycol mixtures in the presence of succinate at pH 4.2, was used to collect synchrotron diffraction data to 1.9 A resolution, in space group R3, a = b = 86.62, c = 62.23 A. Mercury and platinum derivative data were collected at wavelengths to optimize the anomalous contribution. The resulting 2.2 A MIRAS phases differed from the final set by 40 degrees on average and produced an excellent map which was easy to interpret. The model contains 132 water molecules and refined to an R value of 13.7%. 136 residues have clear electron density out of 152 expected from the gene sequence. The 16 C-terminal residues are presumably disordered in the crystal lattice. The monomer is a 'jelly-roll' type, containing mostly beta-sheet and only one short helix. The molecule is a tight trimer. A long C-terminal arm extends from one subunit and encompasses the next one within the trimer contributing to its beta-sheet. Conserved sequence motifs common among dUTPases, previously suggested to compose the active site and confirmed in a recent study of the dUDP complex, are located at subunit-subunit interfaces along the threefold axis, in parts of the beta-sheet and in loop regions. A similar molecular architecture has recently been found in two other trimeric dUTPases.
Amino Acid Sequence↗
Crystallization and preliminary X-ray crystallographic studies of the plant aspartic proteinase cardosin A.
The plant aspartic proteinase cardosin A was crystallized using vapour diffusion. Crystals belong to the monoclinic space group C2, cell dimensions a = 116.9 (2), b = 87.2 (8), c = 81.3 (1) A, beta = 104.4 (4) degrees, and contain two molecules in the asymmetric unit related by a non-crystallographic twofold axis. Diffraction data were collected at room temperature with radiation from a synchrotron source up to 2.85 A resolution. When the crystals were flash cooled to 110 K in a nitrogen stream the same resolution limit could also be obtained on a rotating-anode source. Recently, synchrotron radiation together with flash cooling led to an improvement of the diffraction data to 1.72 A resolution.
Aspartic Acid Endopeptidases↗