β2 microglobulin (β2-M) is a polypeptide that associates with the heavy chain of class I major histocompatibility complex (MHC) antigens on the cell surface. The interaction is dynamic and plays a critical role in the stability of the MHC antigens and their ability to present peptide antigens in CD8+ cells. A transient complex of MHC heavy chain and β2-M is known to be assembled into the TAP molecule (transporter associated with antigen processing) through interactions with a number of chaperones. Binding of processed peptide releases the Class I-β2-M complex to the cell surface. Absence of binding leads to degradation in the proteasome.
