Fischetti V A, Jones K F, Scott J R
J Exp Med. 1985 Jun 1;161(6):1384-401. doi: 10.1084/jem.161.6.1384.
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.
除了特定类型的抗原变异，这是A组链球菌M蛋白的一个众所周知的特征外，我们现在还发现，M分子在分子大小方面存在差异，既存在于不同M型之间，也存在于同一M型内。通过使用与20种不同M蛋白类型发生交叉反应的M6单克隆抗体，以及针对细胞壁N - 乙酰葡糖胺决定簇的抗体，我们能够鉴定出用溶菌酶从链球菌细胞壁释放的M蛋白分子，特别是C组噬菌体相关溶素。对细胞提取物的免疫印迹分析鉴定出与各种细胞壁片段结合的M蛋白分子，这表明M分子与肽聚糖存在连接。从20种不同链球菌血清型中提取的M蛋白显示分子量在41,000至80,000之间存在大小差异。这种极端变异对于相关蛋白来说是不寻常的。在6型链球菌的随机临床分离株中也发现了M分子类似的大小变异。从以下来源分离的M6蛋白未观察到大小变化：(a) 在有限疫情中的菌株，(b) 在小鼠体内传代192次的菌株，以及(c) 在实验室传代156代的菌株，这表明观察到的变异不是一个快速过程。结果表明，在本研究观察到的广泛范围内，M蛋白的大小可能对该分子的抗吞噬活性并不关键。
