Residue conservation of the Z1 sub-lineage α1 and α2 domains among teleosts. Schematic presentation of the human HLA-A2 peptide binding groove defined by the alpha 1 and alpha 2 domains . The 37 residue positions in HLA-A2 known to contribute to the six A through F pockets [1,3] are enlarged and colored black when completely conserved in the aligned teleost Z1 sub-lineage sequences while grey represents teleost sequence identity of 90-99,7%. Ellipses cover those HLA-A2 residues that, according to our sequence alignment, have few or no matching residues in the aligned teleost sequences. The figure is based on 31 Z1 lineage sequences from Atlantic salmon (Salmo salar), zebrafish (Danio rerio), medaka (Oryzias latipes), stickleback (Gasterosteus aculeatus), tilapia (Oreochromis niloticus), tetraodon (Tetraodon nigroviridis), fugu (Takifugu rubripes) and Amazon molly (Poecilia formosa), but excluding the Z1 lineage sequences from cavefish (Astyanax mexicanus). The alignment can be found in Additional file 7: Text S4.