crystal structure of the mhc class i homolog mica a gammadelta t cell ligand the major histocompatibility complex mhc class i homolog mica functions as a stressinducible antigen that is recognized by a subset of gammadelta t cells independent of beta2microglobulin and bound peptides its crystal structure reveals a dramatically altered mhc class i fold both in detail and overall domain organization the only remnant of a peptidebinding groove is a small cavity formed as the result of disordering a large section of one of the groovedefining helices loss of beta2microglobulin binding is due to a restructuring of the interaction interfaces structural mapping of sequence variation suggests potential receptor binding sites on the underside of the platform on the side opposite of the surface recognized by alphabeta t cell receptors on mhc class ipeptide complexes