Blood Group-Active Surface Molecules of the Human Red Blood Cell

Abstract

The surface of the human red blood cell is dominated by a small number of abundant blood group active proteins. The major proteins are the anion transport protein (band 3) which has AB(H) activity, and Glycophorin A which has MN activity. Band 3 and Glycophorin A are of equal abundance in the normal red cell membrane (approximately 10^6 copies of each) and the two proteins may associate together as a complex. The glucose transporter (band 4.5) has AB(H) activity and there are about 5 x 10^5 copies/red cell. Several polypeptides associate together to form the Rh complex. The major components of this complex (abundance 1-2 x 10^5 copies/red cell) are polypeptides of M(r) 30,000, polypeptides of M(r) 45,000-100,000 and Glycophorin B. The antigens of the Rh blood group system appear to be associated with the polypeptides of M(r) 30,000 and those of M(r) 45,000-100,000 (the latter also express AB(H) activity). Glycophorin B expresses the blood group ‘N’ antigen and the Ss antigens. Glycophorins C and D carry the Gerbich antigens and, together, these polypeptides comprise approximately 10^5 copies/red cell. The complete protein sequence of all the above-mentioned proteins is known, except for the M(r) 30,000 and M(r) 45,000-100,000 polypeptides of the Rh complex for which only partial sequences are available, and Glycophorin D, the sequence of which can be inferred from that of Glycophorin C. Several of the minor blood group active proteins at the red cell surface (abundance <1.2 x 10^4 /red cell) have been the subject of recent studies. The polypeptide expressing Cromer-related blood group antigens has been identified as decay-accelerating factor and that carrying the In^a / In^b antigens as CD44. The protein sequence of both of these proteins has been deduced form nucleotide sequencing. The polypeptides expressing Kell antigens, Lutheran antigens, Fy antigens, and LW antigens have also been identified and partially characterised.