To monitor conformational changes in MHC class I structure induced by
interaction with peptide or beta(2)-microglobulin (beta(2)-m), we have
taken a serologic approach. Previous studies by us and others have de
fined circumstances wherein specific peptides can decrease serologic r
ecognition of class I molecules. However, such blocking of serologic e
pitopes has often been interpreted as steric hindrance by peptide side
chains. In this paper, we describe peptide-induced gains in recogniti
on by mAbs 30-5-7, 34-1-2, and B22/249. In experiments with mAb 30-5-7
, impaired reactivity, which resulted from an L(d) loop mutation, was
specifically rescued by the binding of a beta-galactosidase-derived pe
ptide to the L(d) mutant. In studies with mAb 34-1-2, poor L(d) detect
ion was enhanced by mutations in L(d) at beta(2)-m interaction sites o
r by changes within the peptide-binding groove. To evaluate whether kn
own peptides in the L(d) groove could influence 34-1-2 recognition, we
tested six peptide ligands, four of which increased the reactivity of
34-1-2 with the L(d)-expressing cell to various degrees (up to 14-fol
d). It is of interest that L(d) mutations at position 9 and 95/97 made
significant differences in the ranking of the peptides in regard to t
heir ability to increase recognition by 34-1-2 and B22/249. This findi
ng suggests that mutations in the binding groove can alter peptide con
formation and result in secondary changes in class I structure. On the
basis of the cumulative serologic data, we propose that the class I m
olecule displays considerable fluidity, and is structurally influenced
by both beta(2)-m and peptide.