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A soluble derivative of the Enterococcus faecalis JH2-2 class A PBP1 (*PBP1) was overproduced and purified. It exhibited a glycosyltransferase activity on the Escherichia coli 14C-labeled lipid II precursor. As a DD- peptidase, it could hydrolyze thiolester substrates with efficiencies similar to those of other class A penicillin-binding proteins (PBPs) and bind beta-lactams, but with k2/K (a parameter accounting for the acylation step efficiency) values characteristic of penicillin-resistant PBPs.

Penicillin-binding protein 4a (PBP4a) from Bacillus subtilis was overproduced and purified to homogeneity. It clearly exhibits DD-carboxypeptidase and thiolesterase activities in vitro. Although highly isologous to the Actinomadura sp. strain R39 DD-peptidase (B. Granier, C. Duez, S. Lepage, S. Englebert, J. Dusart, O. Dideberg, J. van Beeumen, J. M. Frère, and J. M. Ghuysen, Biochem. J. 282:781-788, 1992), which is rapidly inactivated by many beta-lactams, PBP4a is only moderately sensitive to these compounds. The second-order rate constant (k(2)/K) for the acylation of the essential serine by benzylpenicillin is 300,000 M(-1) s(-1) for the Actinomadura sp. strain R39 peptidase, 1,400 M(-1) s(-1) for B. subtilis PBP4a, and 7,000 M(-1) s(-1) for Escherichia coli PBP4, the third member of this class of PBPs. Cephaloridine, however, efficiently inactivates PBP4a (k(2)/K = 46,000 M(-1) s(-1)). PBP4a is also much more thermostable than the R39 enzyme.