Biomedical subjects

L Mourey

Publications and source records attributed to L Mourey.

25 records · Page 2Linked to original sources

PubMed1997

Small-angle X-ray scattering and crystallographic studies of arcelin-1: an insecticidal lectin-like glycoprotein from Phaseolus vulgaris L.

Arcelin-1 and alpha-amylase inhibitor are two lectin-like glycoproteins expressed in the seeds of the kidney bean (Phaseolus vulgaris). They display insecticidal activities and protect the seeds from predation by larvae of various bruchids through different biological actions. Solution-state investigations by small-angle X-ray scattering (SAXS) show the dimeric structure of arcelin-1, a requirement for its hemagglutinating properties. Anions were found to have specific properties in their effectiveness to disrupt protein aggregates, affect solubility, and improve crystallizability. The SAXS results were used to improve crystallization conditions, and single crystals diffracting beyond 1.9 A resolution were obtained. X-ray diffraction data analysis shows that noncrystallographic symmetry-related arcelin-1 molecules form a lectin-like dimer and reveals the presence of a solvent-exposed anion binding site on the protein, at a crystal-packing interface. The solution state properties of arcelin-1 and crystal twinning may be explained by the anion specificity of this binding site.

Amino Acid Sequence↗

PubMed1996

Structural basis of extended spectrum TEM beta-lactamases. Crystallographic, kinetic, and mass spectrometric investigations of enzyme mutants.

The E166Y and the E166Y/R164S TEM-1 beta-lactamase mutant enzymes display extended spectrum substrate specificities. Electrospray mass spectrometry demonstrates that, with penicillin G as substrate, the rate-limiting step in catalysis is the hydrolysis of the E166Y acyl-enzyme complex. Comparison of the 1.8-A resolution x-ray structures of the wild-type and of the E166Y mutant enzymes shows that the binding of cephalosporin substrates is improved, in the mutant enzyme, by the enlargement of the substrate binding site. This enlargement is due to the rigid body displacement of 60 residues driven by the movement of the omega-loop. These structural observations strongly suggest that the link between the position of the omega-loop and that of helix H5, plays a central role in the structural events leading to extended spectrum TEM-related enzymes. The increased omega-loop flexibility caused by the R164S mutation, which is found in several natural mutant TEM enzymes, may lead to similar structural effects. Comparisons of the kinetic data of the E166Y, E166Y/R164S, and R164S mutant enzymes supports this hypothesis.

Amino Acid Sequence↗

PubMed1995

Electrostatic analysis of TEM1 beta-lactamase: effect of substrate binding, steep potential gradients and consequences of site-directed mutations.

BACKGROUND: Escherichia coli TEM1 is a penicillinase and belongs to class A beta-lactamases. Its naturally occurring mutants are responsible for bacterial resistance to beta-lactamin-based antibiotics. X-ray structure determinations show that all class A beta-lactamases are similar, but, despite the numerous kinetic investigations, the reaction mechanism of these enzymes is still debated. We address the questions of what the molecular contexts during the acylation and deacylation steps are and how they contribute to the efficiency of these penicillinases. RESULTS: Electrostatic analysis of the 1.8 A resolution refined X-ray structure of the wild-type enzyme, and of its modelled Michaelis and acyl-enzyme complexes, showed that substrate binding induces an upward shift in the pKa of the unprotonated Lys73 by 6.4 pH units. The amine group of Lys73 can then abstract the Ser70 hydroxyl group proton and promote acylation. In the acyl-enzyme complex, the deacylating water is situated between the carboxylate group of Glu166, within the enzyme, and the estercarbonyl carbon of the acyl-enzyme complex, in an electrostatic potential gradient amounting to 30 kTe-1 A-1. Other residues, not directly involved in catalysis, also contribute to the formation of this gradient. The deacylation rate is related to the magnitude of the gradient. The kinetic behavior of site-directed mutants that affect the protonation state of residue 73 cannot be explained on the basis of the wild-type enzyme mechanism. CONCLUSIONS: In the wild-type enzyme, the very high rates of acylation and deacylation of class A beta-lactamases arise from an optimal chemical setup in which the acylation reaction seems triggered by substrate binding that changes the general base property of Lys73. In site-directed mutants where Lys73 is protonated, acylation may proceed through activation of a water molecule by Glu166, and Lys73 contributes as a proton shuffle partner in this pathway.

Acylation↗

PubMed1993

Crystal structure of cleaved bovine antithrombin III at 3.2 A resolution.

The crystal structure of cleaved antithrombin III (ATIII) has been determined to 3.2 A resolution by single isomorphous replacement, real space density modification and phase extension protocols. The heavy-atom sites and the first molecular envelope were determined owing to the molecular replacement solution previously reported and partially refined. Refinement of the two molecules of the asymmetric unit led to a crystallographic R-factor of 0.212 for all reflections between 8.0 and 3.2 A, without inclusion of water molecules. The root-mean-square deviation from ideal values is, respectively, 0.015 A and 3.6 degrees for bond lengths and bond angles. The topology of the molecule closely resembles that of cleaved serpins inhibitors with the two residues forming the reactive bond at opposite ends of the molecule. The most significant difference between ATIII and alpha 1-antitrypsin lies in the 45 residue N-terminal extension in ATIII which contribute to the definition of the heparin binding site. This loop region at the surface of the molecule is held by two disulphide bridges to the protein core and exhibits high temperature factor values. It forms a valley which restrains the possibilities for binding of heparin. Docking of the pentasaccharide unit which represents the minimum fragment of heparin able to bind to ATIII indicates a possible role for arginine 14 in the interaction of heparin and the protein.

Amino Acid Sequence↗

PubMed1993

Crystal structure of Escherichia coli TEM1 beta-lactamase at 1.8 A resolution.

The X-ray structure of Escherichia coli TEM1 beta-lactamase has been refined to a crystallographic R-factor of 16.4% for 22,510 reflections between 5.0 and 1.8 A resolution; 199 water molecules and 1 sulphate ion were included in refinement. Except for the tips of a few solvent-exposed side chains, all protein atoms have clear electron density and refined to an average atomic temperature factor of 11 A2. The estimated coordinates error is 0.17 A. The substrate binding site is located at the interface of the two domains of the protein and contains 4 water molecules and the sulphate anion. One of these solvent molecules is found at hydrogen bond distance from S70 and E166. S70 and S130 are hydrogen bonded to K73 and K234, respectively. It was found that the E. coli TEM1 and Staphylococcus aureus PC1 beta-lactamases crystal structures differ in the relative orientations of the two domains composing the enzymes, which result in a narrowed substrate binding cavity in the TEM1 enzyme. Local but significant differences in the vicinity of this site may explain the occurrence of TEM1 natural mutants with extended substrate specificities.

Binding Sites↗

PubMed1990

Antithrombin III: structural and functional aspects.

Antithrombin III is a plasma glycoprotein responsible for thrombin inhibition in the blood coagulation cascade. The X-ray structure of its cleaved form has been determined and refined to 3.2 A resolution. The overall topology is similar to that of alpha 1-antitrypsin, another member of the serpin (serine protease inhibitor) superfamily. The biological activity of antithrombin III is mediated by a polysaccharide, heparin. The binding site of this effector is described. A possible structural transition from the native to the cleaved structure is discussed.

Amino Acid Sequence↗

PubMed1989

Crystallization and preliminary crystallographic data for bovine antithrombin III.

Crystals of bovine antithrombin III were obtained in the presence of metal ions with ammonium sulphate as precipitating agent. Crystals belong to space group P4(1)2(1)2 or P4(3)2(1)2 with cell parameters a = b = 91.4 A, c = 383.1 A; there are two molecules per asymmetric unit. Electrophoresis experiments and amino acid sequence analysis of the N-terminal part of redissolved crystals suggest that the protein molecules are cleaved at the active site.

Animals↗