1gce

From Proteopedia

STRUCTURE OF THE BETA-LACTAMASE OF ENTEROBACTER CLOACAE GC1

Overview

A class C beta-lactamase from a clinical isolate of Enterobacter cloacae, strain GC1 with improved hydrolytic activity for oxyimino beta-lactam, antibiotics has been analyzed by X-ray crystallography to 1.8 A, resolution. Relative to the wild-type P99 beta-lactamase, this natural, mutant contains a highly unique tandem repeat Ala211-Val212-Arg213 [Nugaka, et al. (1995) J. Biol. Chem. 270, 5729-5735]. The 39.4 kDa chromosomal, beta-lactamase crystallizes from poly(ethylene glycol) 8000 in potassium, phosphate in space group P2(1)2(1)2 with cell dimensions a = 78.0 A, b =, 69.5 A, and c = 63.1 A. The crystal structure was solved by the molecular, replacement method, and the model has been refined to an R-factor of 0.20, for all nonzero data from 8 to 1.8 A. Deviations of model bonds and angles, from ideal values are 0.008 A and 1.4 degrees, respectively. Overlay of, alpha-carbon atoms in the GC1 and P99 beta-lactamases results in an rms, deviation of 0.6 A. Largest deviations occur in a loop containing Gln120, and in the Omega loop region (200-218) where the three residues 213-215, are disordered. Possibly as a result of this disorder, the width of the, opening to the substrate binding cavity, as measured from the 318-324, beta-strand to two loops containing Gln120 and Tyr150 on the other side, is 0.6-1.4 A wider than in P99. It is suggested that conformational, flexibility in the expanded Omega loop, and its influence on adjacent, protein structure, may facilitate hydrolysis of oxyimino beta-lactams by, making the acyl intermediate more open to attack by water. Nevertheless, backbone atoms in core catalytic site residues Ser64, Lys67, Tyr150, Asn152, Lys318, and Ser321 deviate only 0.4 A (rmsd) from atoms in P99. A, rotation of a potential catalytic base, Tyr150, relative to P99 at pH 8, is consistent with the requirement for a lower than normal pK(a) for this, residue.

About this Structure

1GCE is a Single protein structure of sequence from Enterobacter cloacae. Active as Beta-lactamase, with EC number 3.5.2.6 Structure known Active Site: ASA. Full crystallographic information is available from OCA.

Reference

Structure of the extended-spectrum class C beta-lactamase of Enterobacter cloacae GC1, a natural mutant with a tandem tripeptide insertion., Crichlow GV, Kuzin AP, Nukaga M, Mayama K, Sawai T, Knox JR, Biochemistry. 1999 Aug 10;38(32):10256-61. PMID:10441119

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