Johnson R H, Beachey E H
Infect Immun. 1979 Sep;25(3):1051-9. doi: 10.1128/iai.25.3.1051-1059.1979.
R protein was extracted from type 3 group A streptococci with hot (95 degrees C) HCl and was purified by ammonium sulfate precipitation followed by molecular-sieve and ion exchange chromatography. Although the R3 antigen was present in a heterogeneous population of proteins ranging from 78,000 to 100,000 daltons in size, we were able to separate an R-rich fraction that contained minimal amounts of heterogeneous proteins as indicated by electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. The final yield of the purified R protein was approximately 15 mug (dry weight) per g (wet weight) of washed and sedimented streptococci. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated a molecular size of approximately 78,000 daltons. Amino acid analysis showed lysine, glutamic acid, alanine, and aspartic acid as the predominant amino acids. A detailed comparison of the purified R3 protein with type 3 M protein indicated a similarity in composition and order of frequency of amino acids. However, the R3 antigen was found to be distinctive from the M3 antigen in agar gel diffusion tests. In addition, R3 and M3 proteins behaved differently in opsonophagocytosis tests and opsonization inhibition tests. Thus, R3 and M3 proteins produced precipitin lines of nonidentity with an unabsorbed antiserum against whole type 3 streptococci: M3-specific antiserum, but not R3-specific antiserum, enhanced the phagocytosis of type 3 streptococci. Purified M3 but not R3 protein was capable of inhibiting the type-specific opsonization of type 3 streptococci. The physicochemical resemblance between M and R proteins in general suggests a common genetic origin. Perhaps R proteins are variant forms of M proteins from which the antiopsonic determinant has been deleted.
用热（95摄氏度）盐酸从A群3型链球菌中提取R蛋白，并通过硫酸铵沉淀，随后进行分子筛和离子交换色谱法进行纯化。尽管R3抗原存在于大小从78,000到100,000道尔顿不等的异质蛋白质群体中，但我们能够分离出一个富含R的组分，通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳显示该组分含有极少量的异质蛋白质。纯化后的R蛋白的最终产量约为每克（湿重）洗涤并沉淀的链球菌15微克（干重）。十二烷基硫酸钠-聚丙烯酰胺凝胶电泳显示其分子大小约为78,000道尔顿。氨基酸分析表明赖氨酸、谷氨酸、丙氨酸和天冬氨酸是主要氨基酸。纯化的R3蛋白与3型M蛋白的详细比较表明，它们在氨基酸组成和频率顺序上具有相似性。然而，在琼脂凝胶扩散试验中发现R3抗原与M3抗原不同。此外，R3和M3蛋白在调理吞噬试验和调理抑制试验中的表现也不同。因此，R3和M3蛋白与针对全3型链球菌的未吸收抗血清产生非同一性沉淀线：M3特异性抗血清而非R3特异性抗血清增强了3型链球菌的吞噬作用。纯化的M3蛋白而非R3蛋白能够抑制3型链球菌的型特异性调理作用。一般来说，M蛋白和R蛋白之间的物理化学相似性表明它们有共同的遗传起源。也许R蛋白是M蛋白的变体形式，其中抗调理决定簇已被删除。
