The penicillin-binding proteins (PBPs) are ubiquitous bac-terial enzymes involved in cell wall biosynthesis,and are the targets of theb-lactam antibiotics. The low molecular mass Neisseria gonorrhoeaePBP 4 (NG PBP 4) is the fourthPBP revealed in the gonococcal genome. NG PBP 4 was cloned, overexpressed,purified,and characterized for b-lactam binding,DD-carboxypeptidase activity,acyl-donor substrate specificity,transpeptidase activity, inhibitionby a number of active site directed reagents,and pHprofile