Blood group MNSs-active sialoglycoproteins of the human erythrocyte membrane.

The human erythrocyte membrane contains at least four different PAS-staining sialic acid-rich glycoproteins. The major sialoglycoprotein, which carries blood group M or N antigen activity, has been extensively characterized. The Ss antigens are located on a minor sialoglycoprotein, which also has "N' activity. The amino acid sequence at positions 1 and 5 of these glycoproteins correlates with the presence of M or N antigen activity. Little is known about the other minor sialoglycoproteins (beta and gamma). Membranes from erythrocytes of type (En(a-)Fin lack the major MN-active sialoglycoprotein; those from S-s-erythrocytes lack normal Ss-active sialoglycoproteins, although they contain an abnormal component that may be an altered Ss glycoprotein. Mk Mk cells lack both the MN- and Ss-active glycoproteins. These sialoglycoprotein-deficient cells are found in apparently healthy individuals. The sera of individuals with sialoglycoprotein-deficient cells may contain antisialoglycoprotein antibody, which has properties similar to those of auto-anti-Pr. Miltenberger Class III, IV, and VI erythrocytes have abnormal Ss-active sialoglycoproteins. Component beta appears altered in Miltenberger Classes I and II. These abnormalities may account for the unique serological properties of Class I, II, III, IV, and VI erythrocytes. Membranes from erythrocytes of type EnU K/Mk, Miltenberger Class V, and Ph contain abnormal sialogylcoproteins that may result from fusion of the genes that give rise to the Mn-and Ss-active sialoglycoproteins. If this is so, then the genes giving rise to the MN and Ss glycoproteins must be adjacent on the same chromosome.