Protein A is a highly stable surface receptor which is capable of binding the Fc portion of immunoglobulins, especially IgGs, from a large number of species

• From Staphylococcus aureus (Cowan strain)
• Each protein A molecule can bind 2 molecules of IgG
• Allows the formation of a precipitate
• Binding to Human IgG Agarose ≥95%

Protein A may be coupled to a wide variety of reporter molecules including fluorescent dyes, enzyme markers, biotin, colloidal gold and radioactive iodine without affecting the antibody binding site. These conjugates may be used to track immunoglobulins in histochemical, western and ELISA applications. Alternatively, protein A may be immobilized onto a solid support to facilitate the purification and recovery of either polyclonal or monoclonal immunoglobulins. Immobilized protein A has recently been applied therapeutically to treat a variety of humoral diseases.

Protein A may be conjugated with various reporter molecules including fluorescent dyes (FITC), enzyme markers (peroxidase, β-galactosidase, alkaline phosphatase), biotin, and colloidal gold without affecting the antibody binding site on the molecule. These conjugates are used to detect immunoglobulins in various immunochemical assays including western blotting, immunohistochemistry, and ELISA applications. In addition, protein A may be immobilized on a solid support such as agarose or acrylic beads for the purification of either polyclonal or monoclonal immunoglobulins. It is also routinely used for immunoprecipitation assays.

Protein A is a highly stable cell surface receptor produced by several strains of Staphylococcus aureus. It consists of a single polypeptide chain of molecular weight 42 kDa, containing four repetitive domains rich in aspartic and glutamic acids but devoid of cysteine. It contains little or no carbohydrate and only 4 tyrosine residues and no tryptophans. Protein A is capable of binding to the Fc portion of immunoglobulins, especially IgGs, from a large number of species. One protein A molecule has been shown to bind at least 2 molecules of IgG simultaneously. The IgG binding domain of Protein A consists of three anti-parallel α-helicies, the third of which is disrupted when the protein is complexed with the Fc region of the immunoglobulins. Protein A will bind the Fc portion of human IgG subclasses, IgM, IgA and IgE; and mouse IgG1 (weakly), IgG2a, and IgG2b. Protein A also binds IgGs from other species, including monkey, rabbit, pig, guinea pig, dog, and cat. Protein A also participates in a number of different protective biological functions including anti-tumor, toxic, and carcinogenic activities. In addition to acting as an immunomodulator, it also has antifungal and antiparasitic properties.