Alignment of amino acid sequences of IZUMO1 homologues from various mammalian species. (A) Amino acids identical in IZUMO1 proteins of bovine, human, mouse and pig. Amino-acid identity is represented by shaded boxes. Arrows indicate putative starting points of the signal sequence and the immunoglobulin (Ig) domain. The transmembrane domain is underlined. (B) Phylogenetic tree showing the similarity of amino acid sequences across mouse, rabbit, goat, sheep, cow, pig, chimpanzee, orangutan, and human IZUMO1 protein. These proteins have been highly conserved.