Eight nonamer peptides that comply with the major anchor residue motifs (the combination of amino acid residues at positions 2 and 9), R-K and R-R, of HLA-B27 (B*2705)-binding peptides were synthesized and tested for their direct binding to HLA class I alpha chains by the HLA class I alpha chain refolding assay previously described. One was a known B27 (B*2705)-binding heat shock protein peptide, HSP89α (201-209), and the other seven were derived from the sequence of wild-type P53, a human tumor suppressor protein. A total of 36 HLA class I allospecificities were tested. HSP89α (201-209) and two P53 peptides, P53 (362-370) and P53 (378-386), all possessing the motif R-K, bound strongly to B27 (B*2705) alpha chains. A weak binding was seen for P53 (272-280) and P53 (334-342), both showing the motif R-R. Most of these B27-binding peptides were found to bind to A3 alpha chains as well. In addition, P53 (173-181) and P53 (334-342), both with the R-R motif, showed substantial binding with A31 alpha chains. All the peptides, carrying the motif R-K also showed weak binding with A31 alpha chains. The remaining two peptides, P53 (201-209) and P53 (282-290), with the motif R-R, did not show significant bininding with any of the alpha chains tested. This study demonstrates both the specificity of peptide binding to a given HLA allelic product and the occurence of cross-peptide-binding between the allelic products of different HLA loci.
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