Amino acid sequence of the blood group Mg-specific major human erythrocyte membrane sialoglycoprotein

Fine specificities of murine anti-Mg monoclonal antibodies

The specificities of two murine anti-Mg monoclonal IgG1 antibodies, 3B10 and 2D5, were determined by pepscan analysis. The peptides which correspond to various fragments of amino-terminal portions of glycophorin A of group M (GPA-M), N (GPA-N) and Mg (GPA-Mg), and replacement analogues of some of these peptides, were synthesized on plastic pins and tested for binding of the antibodies. Both antibodies bound strongly to the N-terminal Mg octapeptide 1LSTNEVAM8, but they showed different subspecificities. The essential fragment of the epitope 2D5 are amino acid residues 2STNEV6. Replacement of any of these amino acid residues by Ala, and replacement of Glu5 residue by Gly, abolished or strongly reduced the antibody binding, but replacement of Asn4 by Thr gave only a moderate decrease of peptide activity. In contrast, the Leu1 and Asn4 residues were most essential components of the epitope 3B10, while Ser2, Thr3 and Glu5 seemed to be less important. Our present results and earlier ones on the specificity of human anti-Mg alloantibodies and monoclonal anti-M/Mg antibodies showed that antibodies reacting with Mg antigen recognize different fragments and/or different amino acid residues of the amino- terminal nonglycosylated domain of GPA-Mg. The knowledge of fine specificities of antibodies reacting with Mg antigen is interesting in view of the presence of anti-Mg alloantibodies in 1-2% of human sera.

Molecular characterization of glycophorin A transcripts in human erythroid cells using RT-PCR, allele-specific restriction, and sequencing

Glycophorin A (GPA) is an erythroid-lineage-specific membrane sialoglycoprotein which occurs in two allelic forms, M and N, which form the antigens of the MN blood group. Purified cDNAs and RNAs isolated from peripheral blood and erythroleukemia cell lines, HEL and K562, were used to develop an RT-PCR technique for amplifying GPA gene transcripts (GYPA). The relative expression of transcripts from the M and N alleles was determined using restriction analysis of these amplified products with four allele-specific restriction endonucleases. The use of this method permits the sensitive identification of GYPA transcripts in these cells and confirms GPA protein expression in the erythroleukemia cell lines and the MN phenotypes of individuals determined by immunolabeling with GPA allele-specific monoclonal antibodies. A novel restriction pattern was obtained using peripheral blood RNA from two individuals with a rare inherited variant allele, GPA Mg. Sequencing of the cDNA obtained using this method revealed a single C to A transversion in the fourth codon in the mature GYPA N coding sequence is responsible for the difference between GYPA Mg and GYPA N.

Amino acid sequence of monkey erythrocyte glycophorin MK. Its amino acid sequence has a striking homology with that of human glycophorin A

A major sialoglycoprotein, glycophorin MK, was isolated from monkey erythrocyte membranes by extraction with lithium diiodosalicylate and partition in aqueous phenol. Chemical analysis of glycophorin MK revealed that the glycophorin consists of 51% protein and 49% carbohydrate by weight, and contains no N-glycosidic oligosaccharide units. Only N-glycolylneuraminic acid (Neu5Gc) was detected as sialic acid. The amino acid sequence of glycophorin MK was determined, which demonstrated that the glycophorin consists of 144 amino acid residues and 18 oligosaccharide units linked O-glycosidically to the peptide backbone through serine or threonine residues. The molecular weight was estimated to be about 35,000 based on the amino acid residues and carbohydrate content. By comparison of the amino acid sequence with those of human, equine and porcine glycophorins, a striking sequence homology was observed between monkey and human glycophorin. Glycophorin MK demonstrated both M and N blood group activities.

Structural analysis of glycophorin A from Miltenberger class VIII erythrocytes

The major human erythrocyte membrane sialoglycoprotein (glycophorin A or MN glycoprotein) was purified from the erythrocytes of two individuals heterozygous for the Mi-VIII gene in the Miltenberger subsystem of the MNSs blood-group system. The complete structure of a tryptic glycopetide from glycophorin A comprising the residues 40-61 was deduced from automated and manual sequence analyses. The Mi-VIII-specific glycophorin A was found to exhibit an arginine----threonine exchange at position 49. The threonine residue was found to be glycosylated. Hemagglutination and hemagglutination inhibition assays demonstrated that one of the Mi-VIII-characteristic antigenic determinants (Anek) is located within the residues 40-61 of glycophorin A. Furthermore, erythrocytes from the two Mi-VIII heterozygotes reacted only weakly with anti-EnaKTsera, suggesting that the Mi-VIII-specific glycophorin A does not express the EnaKT antigen that is located within the positions 46-56 of normal glycophorin A. Our data suggest that the Mi-VIII-specific glycophorin A represents the evolutionary link between normal glycophorin A and the Mi-VIII-specific molecule which exhibits arginine----threonine and tyrosine----serine exchanges at the positions 49 and 52, respectively. Our data also provide an explanation for the close serological similarity between Mi-VII and Mi-VIII erythrocytes.

Structural analysis of the major human erythrocyte membrane sialoglycoprotein from Miltenberger class VII cells

The major human erythrocyte membrane sialoglycoprotein (glycophorin A or MN glycoprotein) was purified from the red blood cells of an individual, homozygous for the Mi-VII gene in the Miltenberger subsystem of the MNSs blood-group system. The complete structure of a tryptic peptide comprising the residues 40-61 of glycophorin A was deduced from manual sequence analyses. The Mi-VII-specific glycophorin A was shown to exhibit an arginine----threonine and a tyrosine----serine exchange at the positions 49 and 52 respectively. The threonine-49 residue was found to be glycosylated. Inhibition assays demonstrated that one of the Mi-VII-specific antigen determinants (Anek) is located within the residues 40-61 of glycophorin A and comprises sialic acid residue(s) attached to O-glycosidically linked oligosaccharide(s). Our data contribute to an understanding of the Miltenberger system and provide an explanation at the molecular level for the previous finding that the erythrocytes from the Mi-VII homozygote lack a high-frequency antigen (EnaKT), located within the residues 46-56 of normal glycophorin A.

A monoclonal anti-glycophorin A antibody recognizing the blood group M determinant: studies on the subspecificity

A mouse monoclonal antibody (425/2B, IgM) was obtained which shows specificity for blood group M determinant of glycophorin A. The antibody is pH-dependent. At pH 6-7 it reacted strongly with blood group M antigen, but also cross-reacted distinctly with N antigen. At pH 8.3 the antibody showed moderately decreased reactivity with M antigen, but no interaction with N antigen was detectable by hemagglutination, immunoblotting, or microplate ELISA. The direct binding studies and inhibition of 425/B antibody by untreated or modified blood group M and N glycoproteins or tryptic glycopeptides showed that the binding to the antigens was not affected by acetylation of their amino groups, or removal of amino-terminal amino acid residue. Desialylation of the antigens decreased their reactivity with the antibody and this effect was distinctly stronger at pH 7 than 8.3. The antibody reacted strongly at pH 7 and 8.3 with glycophorin B of Henshaw phenotype, whereas its reactivity with normal glycophorin B was weak or undetectable at these pH values, respectively. The results obtained indicated that anti-M specificity of 425/2B antibody is related to the 5th amino acid residue of glycophorin A (anti-Mgly specificity) and that pH shift from 7 to 8.3 changes the fine specificity of the antibody. At pH 8.3 the reactivity of the antibody is more dependent on glycine residue (higher anti-M specificity) and less dependent on sialic acid residues in the antigen.

An unusual sialoglycoprotein associated with the Webb-positive phenotype

This paper presents the results of a study on the erythrocyte membrane proteins from Webb-positive individuals. The membrane proteins were separated by polyacrylamide electrophoresis and stained using a Silver stain as well as Coomassie blue and PAS stains. All Webb-positive individuals exhibited a decrease in the beta-sialoglycoprotein beta SGP band along with the appearance of a new SGP 3,000 daltons less than beta SGP. It is postulated that this band is an abnormal beta SGP possibly lacking the N-linked oligosaccharide that is normally present in beta-SGP.

Synthesis of the Mg antigenic determinant and peptide analogs related to human glycophorin A

The Mg antigen is a well known rare mutation of the MN blood group system. The amino-terminal pentapeptide related to human glycophorin AMg, Leu-Ser-Thr-Asn-Glu, as well as pentapeptides representing the peptide backbone of glycophorin AM, AN and AMc and other analogs, were synthesized to serve both as glycosyl transferase acceptors and as artificial antigens. These compounds were obtained by a stepwise peptide coupling strategy in solution.

Studies on Mv red cells. II. Immunochemical investigations

The properties of the Mv antigen, a low incidence receptor of the MNSs blood group system, were investigated by serological tests with protease treated red cells and inhibition assays with glycoproteins or peptides from normal and Mv erythrocytes. Our data demonstrate that the Mv receptor represents an allelomorphic form of the 'N' antigen on the Ss sialoglycoprotein, rather than variant of the M receptor on the MN sialoglycoprotein. Anti-Mv plus -N (serum Arm.) reacts with the N, 'N' and Mv antigens, whereas anti-Mv (serum Arch.) is specifically directed against the latter receptor.

Structural analysis of the Ss sialoglycoprotein specific for Henshaw blood group from human erythrocyte membranes

The N-terminal structures of the MN and Ss erythrocyte membrane sialoglycoproteins (glycophorins A, B) from two Henshaw (He) blood-group heterozygotes were determined by manual sequencing of tryptic glycopeptides and various secondary fragments. No structural alteration of the MN glycoprotein could be detected. The He-specific portion of the Ss glycoprotein was found to exhibit the N-terminal sequence Trp-Ser+-Thr+-Ser+-Gly-(+ = glycosylation). Thus it differs at three positions from its normal counterpart which possesses 'N' activity and exhibits the N-terminal structure Leu-Ser+-Thr+-Thr+-Glu-. Analysis of the Ss glycoprotein from 15 He-negative erythrocyte samples did not reveal any of the three He-specific structural alterations. The presence of a glycine residue at the fifth position of the blood-group-M-active MN glycoprotein as well as in the He-specific Ss glycoprotein provides an explanation for the occurrence of antisera (anti-Me) reacting with the M and He antigens.

Interaction of Vicia graminea anti-N lectin with cell surface glycoproteins from erythrocytes with rare blood group antigens

The erythrocyte receptors for Vicia graminea (Vg) anti-N lectin have been investigated after 125I-labelling of the purified lectin and binding to membrane components separated by dodecyl sulphate polyacrylamide gel electrophoresis. GP alpha (synonym glycophorin A or MN glycoprotein) and GP delta (synonym glycophorin B or Ss glycoprotein) are the main Vg receptors of native human blood group NN and MN erythrocytes whereas Vg lectin only binds to GP delta from MM red cells. The glycoprotein of 28 kDa present in Mi III erythrocytes (a presumed variant of GP delta) carries Vg receptors. Both binding studies and agglutination experiments with this lectin suggest that the delta Mi III gene might produce more glycoprotein molecules than the normal delta gene. Binding of Vg lectin to hybrid glycoproteins [from Mi V, St(a+) and Dantu (+) donors] produced by unequal crossing-over between alpha and delta genes, may occur if the molecules exhibit N activity. The lectin does not bind to sialic acid- and galactose-deficient glycoproteins from Tn erythrocytes and no binding could be detected in the region of GP delta of erythrocytes from S-s-U-individuals. Addition of N-acetylgalactosamine residues to the alkali-labile oligosaccharides attached to GP alpha and GP delta, as found in Cad erythrocytes, decrease the binding capacity for Vg lectin. Finally the absence of Vg lectin binding sites on native GP alpha molecule from MgMg and McM erythrocytes, which carry well defined variants of this glycoprotein, supports the view that the binding site of the lectin on native glycoproteins is located at the N-terminal end of glycoprotein (GP alpha and GP delta) with N specificity (N-terminus = Leu).

Structures of Miltenberger class I and II specific major human erythrocyte membrane sialoglycoproteins

The N-terminal structures of the Miltenberger (Mi-) blood group class I and II specific human MN erythrocyte membrane sialoglycoproteins were determined by manual sequencing of tryptic glycopeptides and various secondary fragments. The Mi-I and Mi-II active glycoproteins were found to exhibit a threonine leads to methionine and threonine leads to lysine exchange, respectively, at position 28 which prevents N-glycosylation of asparagine 26. Due to the absence of the N-glycosidic oligosaccharide chain, the monomeric form of the Mi-I and Mi-II specific glycoproteins possesses a slightly increased sodium dodecyl sulfate/polyacrylamide gel electrophoretic mobility, in comparison to its normal counterpart. Serological studies suggest that antibodies, specific for Mi-I or Mi-II red cells, react with the structurally altered region of the MN glycoprotein.

Susceptibility to invasion by Plasmodium falciparum of some human erythrocytes carrying rare blood group antigens

Tn and Cad erythrocytes which carry unusual carbohydrate moieties attached to glycophorin A and B, the main red cell membrane sialoglycoproteins, resist invasion by the malarial parasite Plasmodium falciparum. Tn red cells are defective in sialic acid and galactose whereas Cad erythrocytes are characterized by a normal sialic acid content but the presence of an additional N-acetylgalactosamine residue attached to each sialotetrasaccharide chain O-glycosidically linked to glycophorin A and B. Homozygous MgMg red cells, which are defective in the cluster of three sialotetrasaccharide chains located at positions 2, 3 and 4 of glycophorin A, are normally invaded. Erythrocytes typed McM carry a glycophorin A molecule intermediate between those from M and N (amino acid substitution at position 1 or 5) but are, like control MN red cells, susceptible to invasion. These results suggest that the primary requirement for entry of P. falciparum merozoites into human red cells is the recognition of a carbohydrate structure present on glycophorin A or B which includes sialic acid and galactose, but is not necessarily clustered at the N-terminal end of the molecule.

Study of a family with a variant M antigen

Anti-M antibody was found in the serum of a 64-year-old woman during a routine pre-operative screen. Her red cell type was MN but the antibody was shown not to be an autoantibody. Blood tests were run on other members of her family, and it was found that her sister's red cells, also type MN, were not agglutinated by the patient's IgM antibody. Chemical studies are reported on the red cell surface glycoproteins of the patient and 2 family members. This red cell variant is compared with previous reports of Ma and is believed to be a further example of this blood type.

N-terminal amino acid sequence of sialoglycoprotein D (glycophorin C) from human erythrocyte membranes

The amino acid sequence of the N-terminal tryptic glycopeptide from a minor human erythrocyte membrane sialoglycoprotein (component D or glycophorin C) was determined by manual sequencing. The glycosylation sites were identified by a new procedure for the detection of the glycosylated derivatives released by Edman degradation. The fragment, comprising 47 residues, was found to contain an average of about 12 O-glycosidically linked oligosaccharides and one asparagine-linked carbohydrate chain. An identical hexapeptide sequence occurring in two regions of the glycopeptide provides evidence that it has developed by an internal gene duplication during evolution. In addition, a part of its structure shows a striking similarity to the sequence of a certain region of the MN and Ss erythrocyte membrane sialoglycoproteins (glycophorins A and B), suggesting that the molecules might be related.

Pj variant, a new hybrid MNSs glycoprotein of the human red-cell membrane

An unusual glycoprotein variant (Pj) was found inherited through a caucasian family exhibiting atypical N and Nvg blood-group reactivities. Pj erythrocytes are blood-group-MS homozygous and have a normal sialic acid content. On sodium dodecyl sulphate/polyacrylamide-gel electrophoresis the variant contains a new component Pj of 24kDa apparent molecular mass in the monomeric state which is sharply stained by periodic acid/Schiff reagent. Both blood-group-MN (alpha) and -Ss (delta) glycoproteins were present. Homodimers (Pj2) as well as heterodimers with MN-glycoprotein (alpha Pj) and the Ss-glycoprotein (delta Pj) were also identified. The new sialoglycoprotein Pj is trypsin- and chymotrypsin-resistant in situ and carries N- and Nvg- but not M- and S-reactivities. The Pj component is labelled by lactoperoxidase-catalysed radioiodination. A 3H label is also easily introduced into the sialic acid or the galactose and galactosamine of the Pj glycoprotein. It is proposed that the Pj is a hybrid glycoprotein containing the N-terminal end of delta-glycoprotein and the C-terminal end of the alpha-glycoprotein. This proposal is supported by the finding that Pj carries a leucine residue at its N-terminus and is not immunoprecipitated by a monoclonal mouse antibody (R18) reacting specifically with the external domain of glycoprotein alpha. The red cells from the proposita Pj were found positive for a very low frequency MN antigen named Sta.