Positively selected ULBP sites mapped onto the crystal structure of human ULBP3. Positively selected cattle ULBP sites mapped onto the structure of human ULBP3. Tertiary structure of human ULBP3 [PDB: 1KCG, chain C] showing the spatial arrangement of homologous cattle ULBP residues under positive selection (>90% probability) as well as the human ULBP3 residues that interact with the NKG2D molecule. The human ULBP3 backbone appears in blue and green. Twelve of 13 cattle ULBP sites under positive selection are mapped onto the structure, and eleven appear as red space-filling residues. Thirteen of the fourteen human ULBP3 sites that interact with NKG2D appear as yellow space-filling residues. One site corresponding to both a selected cattle ULBP site and a human ULBP3 site that interacts with NKG2D appears in orange.