DIFFERENT FORMS OF STREPTOLYSIN-O PRODUCED BY STREPTOCOCCUS-PYOGENES AND BY ESCHERICHIA-COLI EXPRESSING RECOMBINANT TOXIN - CLEAVAGE BY STREPTOCOCCAL CYSTEINE PROTEASE

To resolve apparent discrepancies in the literature, N-terminal sequen ces of tile active high- and low-molecular-weight (high- and low-M(r)) forms of native streptolysin O (nSLO) purified from Streptococcus pyo genes culture supernatants and of the similar-size high- and low-M(r) forms of recombinant SLO (rSLO) found in the periplasm of Escherichia coli expressing a cloned slo gene were determined. The high-M(r) forms of nSLO and rSLO are identical, reflecting removal of a 31-residue si gnal peptide, but the similar-size low-M(r) forms are very different. Removal of C-terminal sequences by proteases in the E. coli periplasm produces an inactive low-M(r) form of rSLO. In contrast, an active Low -M(r) form of nSLO is produced by proteolytic cleavage between the N-t erminal residues Lys-77 and Leu-78, which was shown to correspond to a n extremely sensitive cleavage site for the pyrogenic exotoxin B-deriv ed streptococcal cysteine protease.