Question

Transpeptidase enzyme activity in bacterial cell wall formation

Answer 1

HMW PBPs are enzymes that are composed of two modules located on the outer surface of the cytoplasm membrane and anchored to the cytoplasmic membrane by an N-terminal, noncleavable signal peptide. The C-terminal module is the penicillin-binding domain, which catalyzes the cross-linking of the PG peptides. Depending on the primary structure and on the catalytic activity of the N-terminal domain, HMW PBPs can be divided in two major classes: A and B . The N-terminal module of HMW class A PBPs, of which PBP1A and PBP1B of E. coli are the prototypes, has transglycosylase activity. This makes class A PBPs capable of both the elongation of glycan strands (transglycosylation) and the formation of cross-links between the peptides (transpeptidation) of PG. Transglycosylation may also be done by monofunctional glycosyl transferases . Class B HMW PBPs, of which PBP2 and PBP3 from E. coli are representatives, have an N-terminal non-penicillin-binding domain whose function is unknown but which has been suggested to be a morphogenetic determinant module . At least in E. coliPBP3, the N-terminal domain is required for the folding and stability of the penicillin-binding module, functioning as an intramolecular chaperone , and it may also provide recognition sites for interaction with other cell division proteins .

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