Sortase-catalysed anchoring of surface proteins to the cell wall of Staphylococcus aureus

Many surface proteins of Gram-positive bacteria are anchored to the cell wa ll envelope by a transpeptidation mechanism, requiring a C-terminal sorting signal with a conserved LPXTG motif. Sortase, a membrane protein of Staphy lococcus aureus, cleaves polypeptides between the threonine and the glycine of the LPXTG motif and catalyses the formation of an amide bond between th e carboxyl-group of threonine and the amino-group of peptidoglycan cross-br idges. S. aureus mutants lacking the srtA gene fail to anchor and display s ome surface proteins and are impaired in the ability to cause animal infect ions. Sortase acts on surface proteins that are initiated into the secretio n (Sec) pathway and have their signal peptide removed by signal peptidase. The S. aureus genome encodes two sets of sortase and secretion genes. It is conceivable that S. aureus has evolved more than one pathway for the trans port of 20 surface proteins to the cell wall envelope.