Protein G is a cell wall protein from group C and G Streptococci with a molecular weight between 40-65 kDa and shows high specificity for the Fc region of immunoglobulin G molecules of many mammalian species. The quality of the resin (Protein G Agarose or equivalent) and stability of the immobilisation is important to avoid leakage of Protein G during the elution procedure.
Protein G affinity chromatography is a rapid one-step purification, which removes most non IgG contaminants and can achieve purities close to homogeneity. It is particularly useful for purifications of tissue culture supernatant, where 10-100 fold concentrations can be achieved.