Production of Recombinant Polypeptides Binding α2-Macroglobulin and Analysis of Their Ability to Bind Human Serum α2-Macroglobulin

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, alpha 2-macroglobulin (alpha 2-M), upstream to the HSA-binding domain. Two recombinant polypeptides GM and GM1 capable of binding to alpha 2-M were obtained using the G4223 strain of a group GStreptococcus, protein G molecule of which interacts with three human blood serum proteins (IgG, HSA, and alpha 2-M). However, polypeptide GM containing three IgG-binding and three HSA-bindings domains and the region binding alpha 2-M has higher molecular mass and higher affinity to alpha 2-M than polypeptide GM1 that includes only the alpha 2-M binding region.