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1iem
From Proteopedia
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Crystal Structure of AmpC beta-lactamase from E. coli in Complex with a Boronic Acid Inhibitor (1, CefB4)
Overview
Third-generation cephalosporins are widely used beta-lactam antibiotics, that resist hydrolysis by beta-lactamases. Recently, mutant, beta-lactamases that rapidly inactivate these drugs have emerged. To, investigate why third-generation cephalosporins are relatively stable to, wild-type class C beta-lactamases and how mutant enzymes might overcome, this, the structures of the class C beta-lactamase AmpC in complex with, the third-generation cephalosporin ceftazidime and with a transition-state, analogue of ceftazidime were determined by X-ray crystallography to 2.0, and 2.3 A resolution, respectively. Comparison of the acyl-enzyme, structures of ceftazidime and loracarbef, a beta-lactam substrate, reveals, that the conformation of ceftazidime in the active site differs from that, of substrates. Comparison of the structures of the acyl-enzyme, intermediate and the transition-state analogue suggests that ceftazidime, blocks formation of the tetrahedral transition state, explaining why it is, an inhibitor of AmpC. Ceftazidime cannot adopt a conformation competent, for catalysis due to steric clashes that would occur with conserved, residues Val211 and Tyr221. The X-ray crystal structure of the mutant, beta-lactamase GC1, which has improved activity against third-generation, cephalosporins, suggests that a tandem tripeptide insertion in the Omega, loop, which contains Val211, has caused a shift of this residue and also, of Tyr221 that would allow ceftazidime and other third-generation, cephalosporins to adopt a more catalytically competent conformation. These, structural differences may explain the extended spectrum activity of GC1, against this class of cephalosporins. In addition, the complexed structure, of the transition-state analogue inhibitor (K(i) 20 nM) with AmpC reveals, potential opportunities for further inhibitor design.
About this Structure
1IEM is a Single protein structure of sequence from Escherichia coli with PO4 and CB4 as ligands. Active as Beta-lactamase, with EC number 3.5.2.6 Full crystallographic information is available from OCA.
Reference
Structures of ceftazidime and its transition-state analogue in complex with AmpC beta-lactamase: implications for resistance mutations and inhibitor design., Powers RA, Caselli E, Focia PJ, Prati F, Shoichet BK, Biochemistry. 2001 Aug 7;40(31):9207-14. PMID:11478888
Page seeded by OCA on Tue Nov 20 17:20:49 2007
