Decreased amounts of cell wall-associated protein A and fibronectin-binding proteins in Staphylococcus aureus sarA mutants due to up-regulation of extracellular proteases

Data have been presented indicating that Staphylococcus aureus cell surface protein can be degraded by extracellular proteases produced by the same ba cterium. We have found that in sarA mutant cells, which produce high amount s of four major extracellular proteases (staphylococcal serine protease [V8 protease] [SspA], cysteine protease [SspB], aureolysin [metalloprotease] [ Aur], and staphopain [Scp]), the levels of cell-bound fibronectin-binding p roteins (FnBPs) and protein A were very low compared to those of wild-type cells, in spite of unaltered or increased transcription of the correspondin g genes. Cultivation of sarA mutant cells in the presence of the global pro tease inhibitor alpha (2)-macroglobulin resulted in a 16-fold increase in c ell-bound FnBPs, indicating that extracellular proteases were responsible f or the decreased amounts of FnBPs in sarA mutant cells. The protease inhibi tor E64 had no effect on the level of FnBPs, indicating that cysteine prote ases were not involved. Inactivation of either ssp or our in the prototype S. aureus strain 8325-4 resulted in a threefold increase in the amount of c ell-bound FnBPs. Inactivation of the same protease genes in a sarA mutant o f 8325-4 resulted in a 10- to 20-fold increase in cell-bound protein A. As the serine protease requires aureolysin to be activated, it can thus be con cluded that the serine protease is the most important protease in the relea se of cell-bound FnBPs and protein A.