Schematic figure of peptide binding groove. Schematic presentation of the human HLA-A2 peptide binding groove defined by the alpha 1 and alpha 2 domains [1,3]. Round red circles indicate HLA-A2 amino acids anchoring peptide N-terminus and cyan circles are residues anchoring peptide C-terminus. Yellow circles show positions of the additional U and P lineage alpha 1 domain cysteines, green circles indicate positions of S lineage cysteines, and brown circles indicate the cysteine pair conserved in most MHC molecules. Orange circle shows the N-linked glycosylation site conserved in most classical MHCI molecules (N86). Ellipses cover those HLA-A2 residues that, according to our sequence alignment, have few or no matching residues in the aligned teleost sequences. The alignment can be found in Additional file 11: Text S8.