Protein A is a surface protein (approximately 56kDa in size) originally discovered within the cell wall of Staphylococcus aureus. While important for bacterial survival, Protein A has beneficial uses in immunology for its high affinity binding to immunoglobulins (especially the IgG isotype). This high affinity property makes Protein A essential in the large scale purification of antibodies.Synonyms: ProA, Staphylococcus A protein