ABCB5 (ATP-binding cassette, subfamily B [DR/TAP] member 5) is a 90 kDa (predicted MW) member of the human P-glycoprotein family of molecules. It is expressed by CD133+ pluripotent pigment stem cells, where it serves as a marker for cells that show a high incidence of polyploidy. Human ABCB5 is 812 amino acids (aa) in length. It is possibly a five transmembrane protein with a 247 aa N-terminal extracellular domain (ECD) (aa 1-247) and a 283 aa C-terminal cytoplasmic region (aa 530-812). The ECD contains one ABC transporter (aa 2-177), while the cytoplasmic region contains a second ABC transporter (aa 570-808). There are two potential splice forms. One shows a seven aa substitution for aa 125-812, while another possesses an alternative start site 445 aa upstream of the standard site. Over aa 141-247, human ABCB5 shares 64% aa identity with mouse ABCB5.
