Alterations in the chemical composition of peptidoglycan of Escherichia coli DH5 alpha induced by the expression of Enterococcus faecalis penicillin binding protein 5.

Low-affinity penicillin binding proteins (PBPs) are a particular class of membrane proteins involved in penicillin resistance in Enterococci and other micro-organisms. This PBP is thought to be capable of taking over the activity of all other PBPs during peptidoglycan synthesis. Unfortunately, nothing is known about the enzymatic activity catalyzed by this PBP, but a transpeptidase/transglycosylase action can be postulated to allow complete peptidoglycan synthesis. Recently, we cloned and expressed in Escherichia coli the PBP5 (a low-affinity PBP) of Enterococcus faecalis (Signoretto, C., Boaretti, M., and Canepari, P.: FEMS Microbiol. Lett. 123, 99-106, 1994). Here we describe some of the effects of this PBP when expressed in E. coli, in terms of increased growth rate and autolysis, and particularly its effects on the fine chemical composition of the E. coli peptidoglycan. A distinct increase in the di- and tripeptide monomers and a parallel decrease in the tetrapeptide monomer are described. The results presented here are explained in terms of a partial action of the postulated transpeptidase/ transglycosylase enzymatic complex which leads to the cleavage of one, two or three amino-acids from the pentapeptide monomer, but is incapable of performing the cross-linking between two side-chains due to lack of the natural substrate which is different from that of E. coli.