Factors essential for L,D-transpeptidase-mediated peptidoglycan cross-linking and ?-lactam resistance in Escherichia coli.

ABSTRACT: The target of ?-lactam antibiotics is the D,D-transpeptidase activity of penicillin-binding proteins (PBPs) for synthesis of 4?3 cross-links in the peptidoglycan of bacterial cell walls. Unusual 3?3 cross-links formed by L,D-transpeptidases were first detected in Escherichia coli more than four decades ago, however no phenotype has previously been associated with their synthesis. Here we show that production of the L,D-transpeptidase YcbB in combination with elevated synthesis of the (p)ppGpp alarmone by RelA lead to full bypass of the D,D-transpeptidase activity of PBPs and to broad-spectrum ?-lactam resistance. Production of YcbB was therefore sufficient to switch the role of (p)ppGpp from antibiotic tolerance to high-level ?-lactam resistance. This observation identifies a new mode of peptidoglycan polymerization in E. coli that relies on an unexpectedly small number of enzyme activities comprising the glycosyltransferase activity of class A PBP1b and the D,D-carboxypeptidase activity of DacA in addition to the L,D-transpeptidase activity of YcbB.

SUBMITTER: Hugonnet JE 

PROVIDER: S-EPMC5089857 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature