PEPTIDE INFLUENCES THE FOLDING AND INTRACELLULAR-TRANSPORT OF FREE MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-I HEAVY-CHAINS

Class I major histocompatibility complex molecules require both beta(2 )-microglobulin (beta(2)m) and peptide for efficient intracellular tra nsport. With the exception of H-2D(b) and L(d), class I heavy chains h ave not been detectable at the surface of cells lacking beta(2)m. We s how that properly conformed class I heavy chains can be detected in a terminally glycosylated form indicative of cell surface expression in H-2(b), H-2(d), and H-2(s) beta(2)m(-/-) concanavalin A (Con A)-stimul ated splenocytes incubated at reduced temperature. Furthermore, we dem onstrate the presence of K-b molecules at the surface of beta(2)m(-/-) cells cultured at 37 degrees C. The mode of assembly of class I molec ules encompasses two major pathways: binding of peptide to preformed ' 'empty'' heterodimers, and binding of peptide to free heavy chains, fo llowed by recruitment of beta(2)m. In support of the existence of the latter pathway, we provide evidence for a role of peptide in intracell ular transport of free class I heavy chains, through analysis of Con A -stimulated splenocytes from transporter associated with antigen proce ssing 1 (TAP1)(-/-), beta(2)m(-/-), and double-mutant TAP1/beta(2)m(-/ -) mice.