Protein A of Staphylococcus aureus and related immunoglobulin receptors produced by streptococci and pneumonococci.

Abstract

Publisher Summary Several hundred strains of staphylococci and related organisms have been tested for the production of cell surface and/or extracellular SPA. Techniques for detecting the cell-bound protein include agglutination of erythrocytes sensitized with SPA-reactive antibody. Results have demonstrated the presence of extracellular as well as cell-bound SPA and implied that SPA on the membrane had easy access to Ig molecules in the fluid phase or bound to cell-surface antigens in such a way that the Fc region could interact with SPA receptors. Indeed, studies have shown that SPA is located primarily on the surface of Cowan strain I and is linked covalently to the peptidoglycan portion of the membrane. Studies on biosynthesis have been carried out in strains that produce cell-bound, as well as extracellular SPA (e.g., Cowan I) or only the extracellular product. The physicochemical properties of SPA prepared by lysostaphin treatment of Cowan strain I are summarized. The high frictional ratio (2:1) and intrinsic viscosity (29 ml/gm) compared to values normally obtained for globular proteins (1.1- 1.25 and 3-4 mg/gm, respectively) suggest that SPA is a relatively elongated molecule. The molecular weight of 42,000 is the average of several determinations and is the generally accepted value. This compares to the molecular weight of 29,500 found in the most active fraction obtained after chromatography of heat-extracted material. This chapter discusses the occurrence, properties, applications, biological activity, and potential significance of Ig receptors produced mainly by staphylococci and streptococci. Although they act primarily as Fc receptors, for this discussion they have been classified more broadly as Ig receptors. This is because SPA displays secondary binding activity localized in the Fab region of certain species and classes of Ig, and this has been reported to be the sole type of activity associated with polyclonal human IgE.