Purification and biochemical characterization of a basic superantigen (SPEX/SMEZ3) from Streptococcus pyogenes

A potent basic superantigen (designated streptococcal pyrogenic exotoxin X, SPEX/SMEZ3) was purified to homogeneity from culture supernatants of a Str eptococcus pyogenes scarlatina strain of type 12 (genotype speA(-), speC(-) ) and characterized. Sequence alignments revealed SPEX to be an allele of t he streptococcal mitogens type Z (SMEZ). The N-terminal amino acid sequence of SPEX was found with LEVDNNSLLR to be identical to the recently describe d acidic superantigen SMEZ. Although SPEX/SMEZ genes were present in all of the streptococcal strains tested, a toxin production could only be detecte d in a small number of strains. The produced toxin concentration in the cul ture supernatants of positive strains differed between 0 and 20 ng ml(-1). The purified SPEX stimulated human T-lymphocytes with V beta 8 specificity at extremely low concentrations (lower than 100 pg ml(-1)). (C) 2000 Publis hed by Elsevier Science B.V. on behalf of the Federation of European Microb iological Societies.