Figure 4.

Principal axis in MHC molecules. (A) Human class I MHC molecule HLA-A0201 (PDB 1hhi). The backbone of the bound antigenic peptide is represented by a ribbon. The black line traces the α carbons of the α chain. The gray line traces the chain of β2 microglobulin. The vertical line represents a principal axis that passes through the peptide-binding groove. (B) Mouse class II MHC molecule I-A^k (PDB 1iak). The peptide and principal axis are as in A. Heavy lines trace the α chain and gray lines, the β chain.