1ylp
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Atomic resolution structure of CTX-M-27 beta-lactamase
OverviewOverview
Extended spectrum beta-lactamases (ESBLs) confer bacterial resistance to, third-generation cephalosporins, such as cefotaxime and ceftazidime, increasing hospital mortality rates. Whereas these antibiotics are almost, impervious to classic beta-lactamases, such as TEM-1, ESBLs have one to, four orders greater activity against them. The origins of this activity, have been widely studied for the TEM and SHV-type ESBLs, but have received, less attention for the CTX-M beta-lactamases, an emerging family that is, now the dominant ESBL in several regions. To understand how CTX-M, beta-lactamases achieve their remarkable activity, biophysical and, structural studies were undertaken. Using reversible, two-state thermal, denaturation, it was found that as these enzymes evolve a broader, substrate range, they sacrifice stability. Thus, the mutant enzyme, CTX-M-16 is eightfold more active against ceftazidime than the, pseudo-wild-type CTX-M-14 but is 1.9 kcal/mol less stable. This is, consistent with a "stability-activity tradeoff," similar to that observed, in the evolution of other resistance enzymes. To investigate the, structural basis of enzyme activity and stability, the structures of four, CTX-M enzymes were determined by X-ray crystallography. The structures of, CTX-M-14, CTX-M-27, CTX-M-9 and CTX-M-16 were determined to 1.10, Angstroms, 1.20 Angstroms, 0.98 Angstroms and 1.74 Angstroms resolution, respectively. The enzyme active sites resemble those of the, narrow-spectrum TEM-1 and SHV-1, and not the enlarged sites typical of, ESBL mutants such as TEM-52 and TEM-64. Instead, point substitutions, leading to specific interactions may be responsible for the improved, activity against ceftazidime and cefotaxime, consistent with observations, first made for the related Toho-1 enzyme. The broadened substrate range of, CTX-M-16 may result from coupled defects in the enzyme's B3 strand, which, lines the active site. Substitutions Val231-->Ala and Asp240-->Gly, which, convert CTX-M-14 into CTX-M-16, occur at either end of this strand. These, defects appear to increase the mobility of B3 based on anisotropic, B-factor analyses at ultrahigh resolution, consistent with stability loss, and activity gain. The unusually high resolution of these structures that, makes such analyses possible also makes them good templates for inhibitor, discovery.
About this StructureAbout this Structure
1YLP is a Single protein structure of sequence from Escherichia coli with SUC and SO4 as ligands. Active as Beta-lactamase, with EC number 3.5.2.6 Full crystallographic information is available from OCA.
ReferenceReference
Atomic resolution structures of CTX-M beta-lactamases: extended spectrum activities from increased mobility and decreased stability., Chen Y, Delmas J, Sirot J, Shoichet B, Bonnet R, J Mol Biol. 2005 Apr 29;348(2):349-62. PMID:15811373
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