1HSA:
reference: The three-dimensional structure of HLA-B27 at 2.1 A resolution suggests a general mechanism for tight peptide binding to MHC., Madden DR, Gorga JC, Strominger JL, Wiley DC, Cell 1992 Sep 18;70(6):1035-48. PMID: 1525820

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).