5f83

Publication Abstract from PubMed

Some members of the class A beta-lactamase family are capable of conferring resistance to the last resort carbapenem antibiotics. A unique structural feature of these clinically important enzymes, referred to as class A carbapenemases, is a disulfide bond between invariant Cys69 and Cys238 residues. It was proposed that this disulfide bond may be responsible for the carbapenemase activity of class A beta-lactamases but this has not yet been validated. We show that disruption of the disulfide bond in the GES-5 carbapenemase by C69G substitution results in only minor decreases in the conferred levels of resistance to the carbapenem imipenem and other beta-lactams. Kinetic and circular dichroism experiments with the GES-5 C69G mutant demonstrate that this drop in antibiotic resistance is due to a decline in the enzyme activity caused by a marginal loss of thermal stability. Atomic resolution crystal structures of the C69G-GES-5 mutant show that the protein architecture is unchanged upon disruption of the disulfide bond, and that the enzyme is fully capable of binding imipenem. Disruption of the disulfide bridge in three other class A carbapenemases, NMCA, SFC-1 and SME-1, severely destabilizes these enzymes and impairs bacterial growth. Structural analysis of these enzymes shows that their diminished stability upon loss of the disulfide bridge, compared to that of GES-5, results from a less intensive hydrogen-bonding network holding together two structural domains. Our results demonstrate that the disulfide bond does not play a direct role in the carbapenemase activity of class A carbapenemases but is essential for their stability.

Role of the conserved disulfide bridge in class A carbapenemases.,Smith CA, Nossoni Z, Toth M, Stewart NK, Frase H, Vakulenko SB J Biol Chem. 2016 Sep 2. pii: jbc.M116.749648. PMID:27590339^[1]

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