Protein A is a cell wall protein of Staphylococcus aureus that can bind the Fc part of immunoglobulin molecule of different species with strong affinity. It consists of a single polypeptide chain of molecular weight 42 kDa, containing four repetitive domains. One protein A molecule has been shown to bind at least 2 molecules of IgG simultaneously.
Recombinant protein A is expressed by E. coli and purified by affinity chromatography to give a purity of 95% or more (Coomassie staining SDS-PAGE). The purification process does not use antibody column affinity chromatography to avoid the possibility of incorporation of unrelated IgG in the product.
Protein A affinity chromatography columns have become widely used as affinity columns for purified antibodies from ascites and serum. They can be used for purification genetically engineered recombinant proteins containing antibody Fc fragments.
Recombinant protein A binds to most human and mouse IgG subclasses (e.g., human IgG1, IgG2, IgG4; mouse IgG2, IgG2a, IgG2b, IgG3). It also binds to cow, guinea pig, hamster, house, pig and rabbit total IgG form. Recombinant protein A can be conjugated to a variety of reporter molecules (fluorescent dyes, enzyme labels, biotin, colloidal gold, radioactive labels, etc.) without affecting its binding to the antibody.
These conjugated protein A derivatives can be used for antibody detection of Western-blot, ELISA, immunohistochemistry.