The amyloid precursor-like protein 2 and the adenoviral E3/19K protein both bind to a conformational site on H-2Kd and regulate H-2Kd expression

A protein of unknown physiological function, called amyloid precursor-like protein 2 (APLP2), forms an association with the murine class I molecule K-d that is up-regulated by the presence of the adenoviral protein E3/19K. We have extended these findings to show that APLP2 and E3/19K associate preferentially with folded Kd and not with the open form. APLP2 was detectable at the cell surface, but its surface expression was not upregulated by the concurrent expression of K-d. Experimental down-regulation of APLP2 expression caused a consistent increase in the surface expression of K-d, indicating that APLP2 normally reduces K-d surface expression. These data suggest a role for APLP2 in controlling the maturation of major histocompatibility complex class I molecules.