Many streptococcal strains bind to two main human blood plasma proteins: IgG and human serum albumin (HSA). Protein G expressed in group C and G streptococci has specific binding regions for these proteins. Protein G in group G streptococcal strains also contains a region binding another human plasma protein, α2-macroglobulin (α2-М), upstream to the HSA-binding domain. Two recombinant polypeptides GM and GM1 capable of binding to α2-М were obtained using the G4223 strain of a group G Streptococcus, protein G molecule of which interacts with three human blood serum proteins (IgG, HSA, and α2-М). However, polypeptide GM containing three IgG-binding and three HSA-bindings domains and the region binding α2-М has higher molecular mass and higher affinity to α2-М than polypeptide GM1 that includes only the α2-М binding region.

中文翻译：

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结合α2-巨球蛋白的重组多肽的产生及其结合人血清α2-巨球蛋白的能力分析

许多链球菌菌株与两种主要的人血浆蛋白结合：IgG 和人血清白蛋白 (HSA)。在 C 组和 G 组链球菌中表达的蛋白 G 具有这些蛋白的特异性结合区。G 组链球菌菌株中的蛋白 G 还包含结合另一种人血浆蛋白 α2-巨球蛋白 (α2-М) 的区域，位于 HSA 结合域的上游。使用 G 组链球菌的 G4223 菌株获得了两种能够与 α2-М 结合的重组多肽 GM 和 GM1，其蛋白 G 分子与三种人血清蛋白（IgG、HSA 和 α2-М）相互作用。然而，包含三个 IgG 结合域和三个 HSA 结合域以及结合 α2-М 的区域的多肽 GM 比仅包含 α2-М 结合区域的多肽 GM1 具有更高的分子量和对 α2-М 的更高亲和力。