SPA Recombinant produced in E.Coli is a single non-glycosylated polypeptide chain fused with 6×His tag at C-terminus. SPA is comprised of 5 IgG-binding domains E-D-A-B-C aligned in series containing 306 amino acids and having a molecular mass of 34.7kDa containing little or no carbohydrate. Cell wall binding region, cell membrane binding region and albumin binding region were removed to ensure the highest specific IgG binding.