Reactions of Peptidoglycan-Mimetic β-Lactams with Penicillin-Binding Proteins in Vivo and in Membranes

Publisher Website
Google Scholar
Abstract
The membrane-bound bacterial d-alanyl-d-alanine peptidases or penicillin-binding proteins (PBPs) catalyze the final transpeptidation reaction of bacterial cell wall biosynthesis and are the targets of β-lactam antibiotics. Rather surprisingly, the substrate specificity of these enzymes is not well understood. In this paper, we present measurements of the reactivity of typical examples of these enzymes with peptidoglycan-mimetic β-lactams under in vivo conditions. The minimum inhibitory concentrations of β-lactams with Escherichia coli-specific side chains were determined against E. coli cells. Analogous measurements were made with Streptococcus pneumoniae R6. The reactivity of the relevant β-lactams with E. coli PBPs in membrane preparations was also determined. The results show that under none of the above protocols were β-lactams with peptidoglycan-mimetic side chains more reactive than generic analogues. This suggests that in vivo, as in vitro, these enzymes do not specifically recognize elements of peptidoglycan structure local to the reaction center. Substrate recognition must thus involve extended structure.