X-Kell Blood Group Precursor Related Protein, X-Linked (XKRX)

XKRX encodes a protein that is related to a component of the XK/Kell complex of the Kell blood group system. The protein has a calculated molecular mass of 53.6 kD and contains 10 predicted transmembrane regions with a large second exoplasmic loop, consistent with the XK family structure.XKRX has 1 predicted N-glycosylation site, 17 possible phosphorylation sites, and a cysteine residue, cys392, in the fifth exoplasmic loop that is conserved with a similar XK cys residue that forms a disulfide bond with the Kell protein. XKRX shares 37% and 45% amino acid identity with XK and XKR3, respectively. XKRX had an experimental molecular mass of 42 kD, smaller than the predicted size, which may be due to XKRX hydrophobicity.