5g18

Publication Abstract from PubMed

The monobactam antibiotic aztreonam is used to treat cystic fibrosis patients with chronic pulmonary infections colonized by Pseudomonas aeruginosa strains expressing CTX-M extended-spectrum beta-lactamases. The protonation states of active site residues that are responsible for hydrolysis have been determined previously for the apo form of a CTX-M beta-lactamase, but not for a monobactam acyl-enzyme intermediate. Here we used neutron and high-resolution X-ray crystallography to probe the mechanism by which CTX-M extended-spectrum beta-lactamases hydrolyze monobactam antibiotics. In these first reported structures of a class A beta-lactamase in an acyl-enzyme complex with aztreonam we directly observed most of the hydrogen atoms (as deuterium) within the active site. Although Lys 234 is fully protonated in the acyl-intermediate, we find that Lys 73 is neutral. These findings are consistent with Lys 73 being able to serve as a general base during the acylation part of the catalytic mechanism, as previously proposed. SIGNIFICANCE: Since their initial discovery beta-lactams have constantly remained the most widely prescribed class of antibiotics due to their excellent safety, efficacy coupled with their high availability. The emergence and dissemination of bacterial resistance via beta-lactamase enzymes to this class of drug is now a serious problem in the clinic, often leaving few treatment options for infections resulting from multiple drug resistant superbugs. Using high resolution X-ray and neutron diffraction we have experimentally located key hydrogen atoms and been able to probe the exact mechanism by which extended-spectrum beta-lactamases are able to hydrolyze monobactam antibiotics.

Active Site Protonation States in an Acyl-enzyme Intermediate of a Class A beta-lactamase with a Monobactam Substrate.,Vandavasi VG, Langan PS, Weiss KL, Parks JM, Cooper JB, Ginell SL, Coates L Antimicrob Agents Chemother. 2016 Oct 24. pii: AAC.01636-16. PMID:27795378^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.