Immunochemical properties of Mg erythrocytes.

The major erythrocyte membrane (MN) sialoglycoprotein in Mg red cells was found to exhibit a slightly decreased sodium-dodecyl-sulphate polyacrylamide gel electrophoretic molecular weight and periodic and/Schiff staining intensity. Mg antigen activity was shown to be associated with this molecule. As judged from chemical modification experiments, no carbohydrate but the glycoprotein's N-terminal amino acid is involved in the Mg receptor site. The endgroup of the glycoprotein was found to leucine and studies involving Staphylococcus aureus V8 protease suggest that a glutamic acid is located at the fifth position of its peptide chain. This indicates that the Mgs gene complex evolved from a mutation of an Ns allele. An amino acido substitution or deletion at the second, third and/or fourth position(s), preventing the glycosylation of all or some of these amino acids, provides an explanation for the properties of Mg erythrocytes.

Mg and Mc: mutations within the amino-terminal region of glycophorin A.

M and N are the two common ("normal") alleles at the MN locus of the MNSs blood group system. The antigens M and N that they determine are located within the amino-terminal region of glycophorin A. In the serologically active and glycosylated (*) fragment of glycophorin AN the sequence is Leu-Ser*-Thr*-Thr*-Glu-, and in that of glycophorin AM it is Ser-Ser*-Thr*-Thr*-Gly-. Mg and Mc are very rare ("variant") alleles of M and N; as to the corresponding antigens, Mg is serologically quite distinct from M and N, while Mc is a compound of both. Erythrocytes of genotypes MgN, MgM, MgMg, and McM, which were the object of the present study, contain normal amounts of glycophorin A in their membrane. In glycophorin AMg the amino-terminal sequence is related to that of glycophorin AN by substitution of asparagine for threonine in position 4, and it is nonglycosylated: Leu-Ser-Thr-Asn-Glu-. The corresponding structure of glycophorin AMc is Ser-Ser*-Thr*-Thr*-Glu-; it is thus closely related to that of glycophorin AN and AM, by substitution of the amino acids in positions 1 or 5, respectively. All of these substitutions can be explained by single base changes. The distinctions in chemical structure not only confirm the location of M and N in this region of glycophorin A, because they are the only differences observed, but also indicate, because they are correlated with the distinctions in antigenic specificity, that M and N are structural genes coding for amino acid sequences. The finding that Mc contains structural features of both M and N suggests that these two forms of glycophorin A have evolved from a common ancestral gene by single base substitutions at sites in the genome coding for amino acids in positions 1 and 5 of the sequence. Carbohydrate structures, however, are also necessary for full expression of antigens M and N. Glycosylation during biosynthesis of residues within the polypeptide appears to depend on a particular protein structure.

[MNSs system, erythrocyte membrane and false paternity exclusion]. / Système MNSs, membrane érythrocytaire et fausse exclusion de parenté.

The modification of the red cell membrane first observed by Darnborough and co-workers in En (a-) and EnaEn heterozygous persons, and characterized by a) exaggerated agglutinability of the cells by various serological reagents, b) decrease of their electric surface charge, and c) reduction of their sialic acid content, is shown to be regularly and, to all appearances, directly associated with weakness or absence of MN antigenic substance; it is not seen in comparable "variants" of the Ss antigens. This type of modified cell membrane is thus found in the presence of Mg, of weak forms of M or N (N2 with or without a positive direct antiglobulin test, or as produced by the gene complexes MS.Sta, Ms.Sta, MsMi.V or NsMi.V) and when antigen production at the MN locus is inhibited, completely or almost completely, by the "operator" genes En or Mk. Apparent exclusions of parentage due to some of the genes involved, particularly Mg, En and Mk, are presented. On the other hand, the NNSs genotypes of members of the 3 known families with an En(a-) propositus are discussed and a revised interpretation of them is given, based on renewed serological studies of the persons concerned. A genetical scheme of the MNSs system, comprising four "structural" loci-Ena MN, U Ss-and three "operators", is proposed.