Figure 6.

I-A^k selectively binds Asp- and Asn-bearing HEL epitopes. (A) I-A^k binds a limited subset of the putative HEL epitopes. There are 21 Asp and Asn residues within HEL that may act as possible P1 anchors for I-A^k binding. Synthetic HEL peptides of these potential epitopes were tested for I-A^k binding. Of these putative epitopes, 11 had no detectable binding, 6 bound weakly, and 4 bound well to I-A^k. (B) Many Asp- and Asn-containing HEL peptides are unable to bind I-A^k. Shown are the P1 and auxiliary anchors corresponding to these nonbinding (NB) peptides. For example, HEL(97-110) possesses a suitable P1 Asp101, with G-N-A-V auxiliary anchors, but was unable to bind I-A^k. Peptides with overlapping potential epitopes were tested with individual Ala substitutions and are grouped together.