Some PBPs from Gram positive bacteria involved in spore peptidoglycan synthesis also belong to subclass B3, e.g. Class B HMW-PBPs can be further divided into subclasses and Escherichia coli PBP3 is paradigmatic of subclass B3 that groups class B PBPs from Gram negative bacteria involved in cell division. The HMW-PBPs group can be subdivided into classes A and B, the LMW group into classes A, B and C.
The former enzymes act as transpeptidases in vivo and are involved in peptidoglycan synthesis while the latter are carboxypeptidases and endopeptidases thought to remodel peptidoglycan during the bacterial life cycle but details of their in vivo activities are not well established. Penicillin-binding proteins belong to the family of acyl-serine transferases and are traditionally separated into high-molecular-weight (HMW) PBPs and low-molecular-weight (LMW) PBPs based on molecular weight and sequence homology –. They are found in all bacteria and represent major targets in anti-biotherapy, especially for the widely used β-lactam antibiotics. The penicillin-binding proteins (PBPs) synthesize and remodel the cell wall peptidoglycan, a major component of the bacterial cell wall that gives the cell its shape and rigidity –.