Conformational restraints and flexibility of 14-meric peptides in complex with HLA-B*3501.

Human HLA-B*3501 binds an antigenic peptide of 14-aa length derived from an alternative reading frame of M-CSF with high affinity. Due to its extraordinary length, the exact HLA binding mode was unpredictable. The crystal structure of HLA-B*3501 at 1.5 A shows that the N and C termini of the peptide are embedded in the A and F pockets, respectively, similar to a peptide of normal length. The central part of the 14-meric peptide bulges flexibly out of the groove. Two variants of the alternative reading frame of M-CSF peptide substituted at P2 or P2 and P9 with Ala display weak or no T cell activation. Their structure differs mainly in flexibility and conformation from the agonistic peptide. Moreover, the variants induce subtle changes of MHC alpha-helical regions implicated as critical for TCR contact. The TCR specifically recognizing this peptide/MHC complex exhibits CDR3 length within the normal range, suggesting major conformational adaptations of this receptor upon peptide/MHC binding. Thus, the potential antigenic repertoire recognizable by CTLs is larger than currently thought.

Structure deposition and release

Data provenance

Publication data retrieved from PDBe REST API8 and PMCe REST API9