RESIDUES IN POCKET-B AND POCKET-F OF HLA-B27 ARE CRITICAL IN THE PRESENTATION OF AN INFLUENZA-A VIRUS NUCLEOPROTEIN PEPTIDE AND INFLUENCE THE STABILITY OF PEPTIDE - MHC COMPLEXES

Six pockets, designated A through F, which extend from the peptide bin ding site of class I HLA molecules, have been postulated to play an im portant role in determining peptide binding specificity. HLA-B27 mutan t molecules with single amino acid substitutions at residues 9his-->ph e, 24thr-->ser, 45glu-->thr, and 67cys-->ala in pocket B; 114his-->asn in pocket D; and 116asp-->phe in pocket F have been generated and cha racterized for their capacity to present an influenza A nucleoprotein peptide (NP 383 - 391) for cytotoxic T lymphocyte recognition. We repo rt here that substitutions in residues 45, 67, and 116 affect presenta tion of NP 383 - 391 when peptide is processed and loaded during viral infection. Using I-125-labeled NP peptide, we demonstrate that substi tutions in residues 67 and 116 alter the stability of NP - HLA-B27 com plexes. A substitution at position 9 of the NP peptide complements the mutation introduced at residue 116, suggesting that the NP peptide bi nds with its carboxy terminal amino acid in pocket F. These findings i ndicate that polymorphic residues within pockets B and F of HLA-B27 pl ay a crucial role in peptide binding and stability of peptide - MHC cl ass I complexes. Furthermore, our results suggest that substitutions a t allele-specific residues within pockets B and F alter the stability of NP - HLA-B27 complexes resulting in the diminution or abrogation of NP presentation during viral infection.