Differential binding of peptides substituted at putative C-terminal anchor residues to HLA-DQ8 and DQ9 differing only at β 57

Abstract

HLA-DQ8 (DQA1 *0302-DQB1 *0302: DQβ 57Ala) and DQ9 (DQA1 *0302-DQB1 *0303: DQβ 57Asp) differ only at β 57, at which polymorphism reportedly confers distinct susceptibility to insulindependent diabetes mellitus (IDDM). To identify the differential peptide binding affected by β 57, we determined DQ9-binding peptides by affinity-based selection of a phage random peptide library using the biotinylated DQ9 complex. Nonconservative single-residue substitution of a high-affinity DQ8and DQ9-binding peptide (1KLPD YVL WSSS TVVGLGAAGA 21) at the underlined residues significantly decreased the peptide binding to DQ8 and DQ9. Affinities of the wild-type 21-mer K 4D YVL WSSS TV 13 and K 4A YAA WAAA TA 13 to DQ8 and DQ9 were practically the same. The K 4D YVL WSSS TV 13-based analogue peptides with substitutions at 12T showed that residues R, K, H, E, D, Q, N, T, S, V, L, I, F, M, W, and Y permitted binding to DQ8, whereas only R, T, V, L, I, F, M, W, and Y did so to DQ9. Thus, significant differences exist between DQ9 and DQ8, in that the majority of polar residues, regardless of their static charges at the residue 12, permitted binding to IDDM-susceptible DQ8. which is not the case for DQ9. The affinities of K 4D YVL WSSS XV 13 and K 4A YAA WAAAA X 13 (where X is T, A, K, D, or I) were almost equal to DQ8 and DQ9, suggesting that DQ8 and DQ9-binding peptide motifs could accept both the 8-mer and 9-mer frames depending on intervening sequences between Nand C-terminal anchor residues. The biochemical basis of peptide-HLA interactions determined by DQβ 57 is discussed.