HLA-B27 peptide presentation

Top panel (A): The three-dimensional structure of the alpha-1 and alpha-2 domains of HLA-B*2705. Numbers identify polymorphic residues among B27 subtypes. A peptide (green) intimately interacts with the groove through hydrogen bonds. Each of six pockets (A-F) can bind the side chain of an individual amino acid. Lower panel: (B) Schematic diagram showing binding of antigenic peptides to HLA-B27 and recognition by the T-cell receptor. The side-chains of peptide "anchor" residues P2, P3 and P9 (C-terminal) are bound in pockets. The side-chains of P1, P4, and P8, which extend out of the peptide-binding groove, are critical for T-cell recognition.