1blh
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(New page: 200px<br /><applet load="1blh" size="450" color="white" frame="true" align="right" spinBox="true" caption="1blh, resolution 2.3Å" /> '''STRUCTURE OF A PHOSPH...)
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STRUCTURE OF A PHOSPHONATE-INHIBITED BETA-LACTAMASE. AN ANALOG OF THE TETRAHEDRAL TRANSITION STATE(SLASH)INTERMEDIATE OF BETA-LACTAM HYDROLYSIS
Overview
The crystal structure of beta-lactamase from Staphylococcus aureus, inactivated by, p-nitrophenyl[[N-(benzyloxycarbonyl)amino]methyl]phosphonate, a, methylphosphonate monoester monoanion inhibitor, has been determined and, refined at 2.3 A resolution. The structure reveals a tetrahedral, phosphorus covalently bonded to the O gamma atom of the active site, serine, Ser70. One of the oxygen atoms bonded to phosphorus is located in, the oxyanion hole formed by the two main-chain nitrogen atoms of Ser70 and, Gln237, and the second bonded oxygen is solvated. The, (benzyloxycarbonyl)aminomethyl group is oriented towards the active site, gully such that the peptide group forms compensating electrostatic, interactions with polar groups on the enzyme. The benzyl group forms a, hydrophobic interaction with Ile239 and an aromatic-aromatic edge-to-face, interaction with Tyr105, which has undergone a conformational transition, relative to the native structure. The mode of binding supports the, proposal that on reaction with the enzyme, the phosphonate generates a, structure analogous to the tetrahedral transition state/intermediate, associated with the acylation step of a normal substrate. The disposition, of the phosphonyl group in this complex is the same as that of the, corresponding phosphoryl group in the complex resulting from the, inhibition of trypsin by diisopropylphosphofluoridate. The structure is, consistent with a mechanism of inactivation that follows an associative, pathway, proceeding via a transition state/intermediate in which, phosphorus is penta-co-ordinated, forming a trigonal bipyramidal geometry, with the phosphonyl donor (p-nitrophenol) and acceptor (Ser70 O gamma, atom) in apical positions. A model of this transition state can be, accommodated in the active site of beta-lactamase without any steric, hindrance. A model of the tetrahedral transition state associated with the, acylation step by benzyl penicillin has been derived. Because of the, conformational rigidity of the fused rings of penicillin molecules, the, orientation of the substrate is fixed once the tetrahedral carbonyl carbon, and its ligands are superimposed on the phosphonate group. The outcome is, that the carboxylate substituent on the thiazolidine ring forms a salt, bridge with Lys234, and the preferred puckering of the ring is that, observed in the crystal structure of ampicillin, the so-called "open", conformer.
About this Structure
1BLH is a Single protein structure of sequence from Staphylococcus aureus with FOS as ligand. Active as Beta-lactamase, with EC number 3.5.2.6 Full crystallographic information is available from OCA.
Reference
Structure of a phosphonate-inhibited beta-lactamase. An analog of the tetrahedral transition state/intermediate of beta-lactam hydrolysis., Chen CC, Rahil J, Pratt RF, Herzberg O, J Mol Biol. 1993 Nov 5;234(1):165-78. PMID:8230196
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