Repeating covalent structure of streptococcal M protein.

Abstract

The covalent structure of the M protein molecule of group A streptococci that is responsible for inducing type-specific, protective immunity was identified. M protein was extracted from type 24 streptococci, purified and cleaved with CNBr. Seven CNBr peptides were purified and further characterized. Together, the peptides account for the entire amino acid content of the M protein molecule. Each of the purified peptides possessed the type-specific determinant that inhibits opsonic antibodies for group A streptococci. The primary structures of the NH2--terminal regions of each of the purified peptides was studied by automated Edman degradation. The partial sequences of 2 of the peptides were identical to each other and to that of the uncleaved M protein molecule through at least the first 27 residues. The NH2--terminal sequences of the remaining 5 peptides were identical to each other through the 20th residue but completely different from the NH2--terminal region of the other 2 peptides. The type-specific immunoreactivity and the incomplete analysis of the primary structure of the 7 peptides suggest that the antiphagocytic determinant resides in a repeating amino acid sequence in the M protein molecule.