ABSTRACT
Group A Streptococcus is a common pathogen that causes pharyngitis, impetigo, myositis, and lethal streptococcal toxic shock syndrome. Streptococcal pyrogenic exotoxin B (SPE B) is strongly associated with the severity of disease. SPE B is a cysteine protease and matures itself by autocatalysis. We found that SPE B was directly associated with human S-adenosylhomocysteine hydrolase (AdoHcyase), an essential factor for a delayed-type immune response. AdoHcyase protein levels and enzymatic activities were significantly higher in human cells infected with the Streptococcus pyogenes SW510 speB mutant strain than in cells infected with the NZ131 wild-type strain. SPE B also inactivated AdoHcyase, shown by a decrease in homocysteine, the main product of AdoHcyase. We found that in vivo and in vitro, SPE B induced hypermethioninemia, which is caused by an AdoHcyase defect. We also found that AdoHcyase is a substrate of SPE B cysteine protease. SPE B, therefore, potentially causes immunosuppression by cleaving AdoHcyase.
