TESTING THE IMPORTANCE OF EACH RESIDUE IN A HLA-B27-BINDING PEPTIDE USING MONOCLONAL-ANTIBODIES

When a peptide derived from histone 3.3 was incubated with mouse L cel ls transfected with HLA-B27, the cells became highly reactive with Ye- 2, an anti-HLA-B27 mAb. The critical residues were analyzed by testing analogues in which each of the nine residues in the peptide was conse cutively substituted by 19 other amino acids. The conclusions were sep arately verified using a different HLA-B27-positive cell line. The abi lity of some of these peptides to bind to HLA-B27 was also assayed by their ability to stabilize HLA-B27 in a mutant cell line which require d HLA-B27-binding peptides to express HLA-B27 at 37-degrees-C. These e xperiments showed that in P4, P5, P6, P7, P8, and P9, all 20 different amino acids could be substituted without eliminating the ability of t he analogues to bind to HLA-B27. The residues which were responsible f or the HLA-B27-peptide complex reacting with the Ye-2 antibody were P8 and P9. The latter might mediate its effect by altering either the su rface conformation of the closely associated HLA-B27 heavy chain or th e conformation of the peptide itself.