Structural highlights
Publication Abstract from PubMedCarbapenems are the last resort antibiotics for treatment of life-threatening infections. The GES beta-lactamases are important contributors to carbapenem resistance in clinical bacterial pathogens. A single amino acid difference at position 170 of the GES-1, GES-2, and GES-5 enzymes is responsible for the expansion of their substrate profile to include carbapenem antibiotics. This highlights the increasing need to understand the mechanisms by which the GES beta-lactamases function to aid in development of novel therapeutics. We demonstrate that the catalytic efficiency of the enzymes with carbapenems meropenem, ertapenem, and doripenem progressively increases (100-fold) from GES-1 to -5, mainly due to an increase in the rate of acylation. The data reveal that while acylation is rate limiting for GES-1 and GES-2 for all three carbapenems, acylation and deacylation are indistinguishable for GES-5. The ertapenem-GES-2 crystal structure shows that only the core structure of the antibiotic interacts with the active site of the GES-2 beta-lactamase. The identical core structures of ertapenem, doripenem, and meropenem are likely responsible for the observed similarities in the kinetics with these carbapenems. The lack of a methyl group in the core structure of imipenem may provide a structural rationale for the increase in turnover of this carbapenem by the GES beta-lactamases. Our data also show that in GES-2 an extensive hydrogen-bonding network between the acyl-enzyme complex and the active site water attenuates activation of this water molecule, which results in poor deacylation by this enzyme. Kinetic and Structural Requirements for Carbapenemase Activity in GES-Type beta-Lactamases.,Stewart NK, Smith CA, Frase H, Black DJ, Vakulenko SB Biochemistry. 2014 Dec 22. PMID:25485972[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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