Position of candidate risk polymorphic residues in HLA-DRB1*1501. a. Cartoon representation of HLA-DRB1 (PDB ID 1BX2) in which the Cα atoms of candidate risk polymorphic residues (Table 2) are represented as small spheres (green). The β1 and β2 domains are labeled. b. Surface and cartoon representation of HLA-DRB! viewed from above the binding groove. The three-dimensional arrangement of the P4 pocket is shown as a grey mesh. The Cα atoms of the polymorphic residues 13 β (green) at the base of the P4 pocket and residue 60 β (orange) are represented as small spheres.