title: Immunochemical properties of streptococcal M protein purified by isoelectric focusing.
abstract: Electrofucusing of an alkaline extract of type 24 streptococcal M protein yielded an antigenic fraction that was type specific and apparently homogeneous. The haptenic nature of this fraction was suggested by its inability to precipitate type-specific antiserum or to induce opsonic antibodies in rabbits, despite its ability to strongly inhibit opsonization of homologous-type streptococci by M antibody. The fraction migrated as a single band upon electrophoresis in sodium dodecyl sulfate (SDS) acrylamide gel. The mobility of the protein band was consistent with a molecular weight of 36,500 daltons. In some experiments using larger quantities of protein, a second faint protein band with an average molecular weight of 70,000 was observed, suggesting the presence of dimers of the 36,500-dalton protein. Amino acid analysis showed the predominant amino acid to be glycine followed by aspartic acid and glutamic acid. Moreover, this M protein fraction was free of non-type-specific immunotoxic properties in guinea pigs and in man. Although apparently not immunogenic, this nontoxic fraction may provide a useful tool to study the relationship of the type-specific protective moiety to potentially harmful "impurities" in M protein vaccines.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D000942:Antigens, Bacterial / Q000032:analysis; D001426:Bacterial Proteins / Q000008:administration & dosage / Q000032:analysis / Q000302:isolation & purification*; D003168:Complement Fixation Tests; D006168:Guinea Pigs; D006801:Humans; D007106:Immune Sera / Q000302:isolation & purification; D007115:Immunization Schedule; D007271:Injections, Intradermal; D007525:Isoelectric Focusing; D009895:Opsonin Proteins / Q000032:analysis; D010587:Phagocytosis; D011817:Rabbits; D012882:Skin Tests; D013297:Streptococcus pyogenes / Q000276:immunology*
chemical_list: D000596:Amino Acids; D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D007106:Immune Sera; D009895:Opsonin Proteins