Size variation of the M protein in group A streptococci.
In addition to the type-specific antigenic variation that is a well-known characteristic for the group A streptococcal M protein, we have now found that the M molecules vary with respect to their molecular size, both between M types and within an M type. By the use of an M6 monoclonal antibody, which crossreacts with 20 different M protein types, and antibodies to the N-acetyl glucosamine determinant of the cell wall, we have been able to identify the M protein molecules released from the streptococcal cell wall with muralytic enzymes, particularly group C phage-associated lysin. Immunoblot analysis of the cell extract identified M protein molecules bound to various cell wall fragments, suggesting a peptidoglycan linkage for the M molecule. M protein extracted from 20 different streptococcal serotypes revealed size variations from 41,000 to 80,000 in molecular weight. This extreme variation is unusual for related proteins. Similar size variations in the M molecule were also found in random clinical isolates of type 6 streptococci. No size change was seen in M6 protein isolated from: (a) strains within a limited epidemic, (b) a strain passaged in mice 192 times, and (c) a strain passaged in the laboratory for 156 generations, suggesting that the observed variation is not a rapid process. The results indicate that, within the broad limits observed in this study, the size of the M protein may not be critical to the antiphagocytic activity of the molecule.
V A
VA
Fischetti
K F
KF
Jones
J R
JR
Scott
D000942:Antigens, Bacterial / Q000276:immunology / Q000302:isolation & purification; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000276:immunology / Q000302:isolation & purification*; D002352:Carrier Proteins; D010450:Endopeptidases; D000939:Epitopes / Q000302:isolation & purification; D008970:Molecular Weight; D009113:Muramidase; D013297:Streptococcus pyogenes / Q000032:analysis* / Q000276:immunology
D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D000939:Epitopes; C014689:streptococcal M protein; D009113:Muramidase; D010450:Endopeptidases; C021816:mutanolysin