ANCHOR STRUCTURE OF STAPHYLOCOCCAL SURFACE-PROTEINS III - ROLE OF THEFEMA, FEMB, AND FEMX FACTORS IN ANCHORING SURFACE-PROTEINS TO THE BACTERIAL-CELL WALL

Surface proteins of Staphylococcus aureus are covalently linked to the bacterial cell wall by a mechanism requiring a COOH-terminal sorting signal with a conserved LPXTG motif, Cleavage between the threonine an d the glycine of the LPXTG motif liberates the carboxyl of threonine t o form an amide bond with the pentaglycyl cross-bridge in the staphylo coccal peptidoglycan. Here, we asked whether altered peptidoglycan cro ss-bridges interfere with the sorting reaction and investigated surfac e protein anchoring in staphylococcal fem mutants. S. aureus strains c arrying mutations in the femA, femB, femAB, or the femAX genes synthes ize altered cross-bridges, and each of these strains displayed decreas ed sorting activity. Characterization of cell wall anchor structures p urified from the fem mutants revealed that surface proteins were linke d to cross-bridges containing one, three, or five glycyl residues, but not to the epsilon-amino of lysyl in muropeptides without glycine, Wh en tested in a femAB strain synthesizing cross-bridges with mono-, tri -, and pentaglycyl as well as tetraglycyl-monoseryl, surface proteins were found anchored mostly to the five-residue cross-bridges (pentagly cyl or tetraglycyl-monoseryl). Thus, although mild-type peptidoglycan appears to be the preferred substrate for the sorting reaction, altere d cell wall cross-bridges can be linked to the COOH-terminal end of su rface proteins.