1znb
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(New page: 200px<br /><applet load="1znb" size="450" color="white" frame="true" align="right" spinBox="true" caption="1znb, resolution 1.85Å" /> '''METALLO-BETA-LACTAMA...)
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Revision as of 05:25, 21 November 2007
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METALLO-BETA-LACTAMASE
Overview
BACKGROUND: The metallo-beta-lactamase from Bacteroides fragilis, hydrolyzes a wide range of beta-lactam antibiotics, and is not clinically, susceptible to any known beta-lactamase inhibitors. B. fragilis is, associated with post-surgery hospital infections, and there has been a, recent report of plasmid-mediated dissemination of the enzyme. Effective, inhibitors are therefore urgently needed. Knowledge of the, three-dimensional structure will aid in the drug design effort. RESULTS:, The crystal structure of the enzyme has been determined by using, multiwavelength anomalous diffraction at the zinc absorption edge and, refined to 1.85 A resolution. The structure is a four-layer, alpha/beta/beta/alpha molecule. The active site, found at the edge of the, beta sandwich contains a binuclear zinc center with several novel, features. One zinc is tetrahedrally coordinated, the other has a trigonal, bipyramidal coordination; a water/hydroxide molecule serves as a ligand, for both metals. The residues that coordinate the two zincs are invariant, in all metallo-beta-lactamases that have been sequenced, except for two, conservative replacements. Despite the existence of the pattern for, binuclear zinc binding, the reported structure of the Bacillus cereus, enzyme contains only a single zinc. CONCLUSIONS: Structural analysis, indicates that affinity for the penta-coordinated zinc can be modulated by, neighboring residues, perhaps explaining the absence of the second zinc in, the B. cereus structure. Models of bound substrates suggest that the, active-site channel can accommodate a wide variety of beta-lactams. We, propose that the zinc cluster prepares an hydroxide, probably the, hydroxide that ligates both zincs, for nucleophilic attack on the carbonyl, carbon atom of the beta-lactam. The resulting negatively charged, tetrahedral intermediate implicated in catalysis is stabilized by an, oxyanion hole formed by the side chain of the invariant Asn 193 and the, tetrahedral zinc.
About this Structure
1ZNB is a Single protein structure of sequence from Bacteroides fragilis with ZN and NA as ligands. Active as Beta-lactamase, with EC number 3.5.2.6 Full crystallographic information is available from OCA.
Reference
Crystal structure of the wide-spectrum binuclear zinc beta-lactamase from Bacteroides fragilis., Concha NO, Rasmussen BA, Bush K, Herzberg O, Structure. 1996 Jul 15;4(7):823-36. PMID:8805566
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