EFFECTS OF BETA(2)-MICROGLOBULIN MUTATIONS ON THE ALPHA-1 HELICAL REGION OF H2-L-D

Beta-2 microglobulin (beta(2)m)has been shown to have an effect on the structural and functional constraints that facilitate proper class I antigen presentation. To date, no evidence has pinpointed the beta(2)m -specific amino acids that play an integral role in affecting structur e in and around the peptide binding region of class I. To delineate be ta(2)m amino acid positions that affect the alpha-1 helical region, we generated a series of mutant beta(2)m proteins bearing precise amino acid substitutions. The amino acid positions chosen were based upon pr evious results which demonstrated that human beta(2)m association with H2-L-d altered the structure of the alpha-1/alpha-2 super-domain. bet a(2)m mutant proteins were used in beta(2)m exchange assays with cells expressing H2-Ld. Following exchange, cells were assayed to determine whether mutant beta(2)m association resulted in structural alteration of class I extracellular domains. The alteration in H2-L-d structure was evidenced by an increase in the binding of an antibody (34-1-2), s pecific for the alpha-1 helical region of H2-L-d. Results demonstrated that amino acid substitutions in beta(2)m positions 33 and 53 led to a dramatic increase in the reactivity of the alpha-1 domain-specific a ntibody 34-1-2. Identifying beta(2)m amino acid positions that influen ce the structure of the peptide binding region may allow for a better understanding of cellular immune responses that center upon class I/be ta(2)m expression.