Anchor structure of staphylococcal surface proteins IV. Inhibitors of the cell wall sorting reaction

Surface proteins of Staphylococcus aureus are covalently linked to the bact erial cell wall by a mechanism requiring a COOH-terminal sorting signal wit h a conserved LPXTG motif. Cleavage between the threonine and the glycine o f the LPXTG motif liberates the carboxyl of threonine to form an amide bond with the amino of the pentaglycine cross-bridge in the staphylococcal pept idoglycan. We asked whether antibiotic cell wall synthesis inhibitors inter fere with the anchoring of surface proteins. Penicillin G, a transpeptidati on inhibitor, had no effect on surface protein anchoring, whereas vancomyci n and moenomycin, inhibitors of cell wall polymerization into peptidoglycan strands, slowed the sorting reaction. Cleavage of surface protein precurso rs did not require a mature assembled cell wall and was observed in staphyl ococcal protoplasts. A search for chemical inhibitors of the sorting reacti on identified methanethiosulfonates and p-hydroxymercuribenzoic acid. Thus, sortase, the enzyme proposed 60 cleave surface proteins at the LPXTG motif , appears to be a sulfhydryl-containing enzyme that utilizes peptidoglycan precursors but not an assembled cell wall as a substrate for the anchoring of surface protein.