Recombinant Protein G

Protein G is a cell wall protein isolated from G Streptococci, which has two IgG binding domains, albumin and a cell surface binding site. The recombinant protein G was expressed in Escherichia coli, which removed albumin and cell surface binding sites and reduced non-specific adsorption. Protein G binds best at pH 5.0, but also works well between pH 7.0-7.2. Compared with Protein A, Protein G has stronger binding ability to IgG of most mammals, and it can also bind rat IgG2a, human IgG3 and mouse IgG1 that cannot bind Protein A well. Protein G does not bind to human IgM, IgD and IgA. The difference in the binding properties of Protein A and Protein G may be due to the different composition of the IgG binding sites of the two proteins.