Altered membrane sialoglycoproteins in human erythrocytes lacking the Gerbich blood group antigens

A Comprehensive Review of Our Current Understanding of Red Blood Cell (RBC) Glycoproteins

Human red blood cells (RBC), which are the cells most commonly used in the study of biological membranes, have some glycoproteins in their cell membrane. These membrane proteins are band 3 and glycophorins A-D, and some substoichiometric glycoproteins (e.g., CD44, CD47, Lu, Kell, Duffy). The oligosaccharide that band 3 contains has one N-linked oligosaccharide, and glycophorins possess mostly O-linked oligosaccharides. The end of the O-linked oligosaccharide is linked to sialic acid. In humans, this sialic acid is N-acetylneuraminic acid (NeuAc). Another sialic acid, N-glycolylneuraminic acid (NeuGc) is present in red blood cells of non-human origin. While the biological function of band 3 is well known as an anion exchanger, it has been suggested that the oligosaccharide of band 3 does not affect the anion transport function. Although band 3 has been studied in detail, the physiological functions of glycophorins remain unclear. This review mainly describes the sialo-oligosaccharide structures of band 3 and glycophorins, followed by a discussion of the physiological functions that have been reported in the literature to date. Moreover, other glycoproteins in red blood cell membranes of non-human origin are described, and the physiological function of glycophorin in carp red blood cell membranes is discussed with respect to its bacteriostatic activity.

Hereditary elliptocytosis: spectrin and protein 4.1R

Hereditary elliptocytosis (HE) is a common disorder of erythrocyte shape, occurring especially in individuals of African and Mediterranean ancestry, presumably because elliptocytes confer some resistance to malaria. The principle lesion in HE is mechanical weakness or fragility of the erythrocyte membrane skeleton due to defects in alpha-spectrin, beta-spectrin, or protein 4.1. Numerous mutations have been described in the genes encoding these proteins, including point mutations, gene deletions and insertions, and mRNA processing defects. Several mutations have been identified in a number of individuals on the same genetic background, suggesting a "founder effect." The majority of HE patients are asymptomatic, but some may experience hemolytic anemia, splenomegaly, and intermittent jaundice.

Fine characterization of a series of new monoclonal antibodies directed against glycophorin A

OBJECTIVES

Glycophorins A (GPA) and B (GPB) are the major sialoglycoproteins of the human erythrocyte (RBC) membrane. To prepare tools for the analysis of GPA and GPB, we produced a series of new monoclonal antibodies (mAbs) that identified epitopes of GPA.

METHODS

Seven murine monoclonal antibodies directed to glycophorin A (GPA) were fully characterized by agglutination of untreated and enzyme-treated human erythrocytes, inhibition of agglutination using chemically modified glycophorins and peptides from GPA, immunoblotting, and binding to synthetic peptides on plastic pins.

RESULTS

The antibodies identify epitopes located on four different portions of GPA. (1) NaM13-6D2 binds to the N-terminal portion of GPA and GPB carrying the N blood group antigen; (2) NaM26-3F4 recognizes the homologous portion of GPA and GPB corresponding to their amino acids 6-26; (3) NaM10-2H12, NaM16-IB10 and NaM10-6G4 are specific for the amino acid sequence 38-45 of GPA; and (4) NaM37-5F4 and NaM13-4E4 bind to the amino acid residues 119-124 located on the intracellular ponion of GPA.

CONCLUSION

These antibodies represent precise tools to investigate GPA and related molecules in different cells and tissues.

Inheritance of abnormal glycophorin C of the Gerbich and Yussef type in a French family

The discovery of a natural Gerbich antigen (anti-Ge2) in the serum of a propositus prompted us to study his red blood cells (RBCs) by using monoclonal anti-bodies (mAbs) directed against glycophorin (GP) C and GPD. An mAb directed against the Ge4 antigen (mAb NaM10-7G11) agglutinated both untreated and trypsin-treated cells, demonstrating the expression of a trypsin-resistant GPC (namely, GPC of the Gerbich type: GPCGe). Surprisingly, an anti-Ge3 antibody (mAb NaM19-3C4) agglutinated untreated cells, showing that they also express the Ge3 antigen that may be carried by normal GPC and CPD or by the abnormal GPC of the Yussef (Yus) type (GPCYus). Immunoblotting analysis performed with an mAb directed against the C-terminal portion of GPC showed that the propositus' RBCs do not contain normal GPC and GPD but both GPCGe and GPCYus. Analysis of RBCs from the family demonstrated that, like the propositus, 2 of the 3 sisters had inherited both the GYPCGe and the GYPCYus alleles from the parents, who carried either the GYPCGe or the GYPCYus allele. The third sister had inherited the normal GYPC alleles from her parents, whereas the child of the propositus had inherited the GYPCGe allele. Interestingly, natural anti-Ge2 antibodies were identified in the serum of 2 of the 3 Ge-negative individuals.

The effect of cysteine modification and proteinases on the major antigens (D, C, c, E and e) of the Rh blood group system

We have confirmed and extended previous observations showing that the (Rh) D antigen of erythrocyte membranes is destroyed by various reagents that modify cysteine (Cys) residues (Res.) and by trypsin as well as chymotrypsin, using thirty examples of monoclonal or polyclonal anti-D in heamglutination inhibition assays. We have also shown that most C, c, E, e and BS58 epitopes are inactivated or weakened by most Cys reagents and by these proteinases, using monoclonal and polyclonal antibodies. Inactivation by 5,5-dithiobis-(2-nitrobenzoic acid) was always fully reversible after subsequent dithioerythritol treatment. The essential Cys Res. appear to be buried in the membrane in view of the inability of some reagents to inactivate (iodoacetamide, iodoacetic acid) or reactivate (reduced glutathione) the antigens. Data obtained with N-ethylmaleimide indicate that inactivation of the C and c antigens is, at least in part, attributable to (a) Cys Res. that is (are) different from that (those) involved in the E and e antigens. Data obtained with the Cys reagents and the proteinases suggest that more than one peptide loop of the Rh proteins is involved in the major Rh antigens.

Biochemical approaches to the detection and characterization of membrane proteins carrying blood group determinants

The investigation of red blood cell membrane proteins carrying blood group determinants mainly involves the use of specific antibodies--polyclonal human antibodies and both murine and human monoclonal antibodies--directed against blood group antigens. Other blood group specific reagents like lectins, also represent useful tools to identify membrane proteins. These reagents allowed the detection and, then the characterization of several red cell membrane components by using a series of methods based on their specific interaction with the corresponding antigen. Reagents and investigation methods are overviewed hereafter.

Gerbich blood groups and minor glycophorins of human erythrocytes

Four main glycophorins which can be specifically detected by periodic-acid-Schiff (PAS) staining after separation of red cell membranes by SDS-polyacrylamide gel electrophoresis have been identified and are known under different nomenclatures. Here, the designation of glycophorins A, B and C and glycophorin D will be used. A new member designated glycophorin E (GPE) has been recently identified in the course of molecular genetic studies. These glycophorins represent about 2% of the total erythrocyte membrane protein mass and have been fully characterized both at the protein and at the DNA level. Accordingly, these molecules can be subdivided into two groups that are distinguished by distinct properties such as blood group antigenic properties, apparent M(r), copy number, attached glycans, detergent solubility, and gene structure. GPC and GPD are minor sialoglycoproteins contributing to 4 and 1% to the PAS-positive material and are present at about 2.0 and 0.5 x 10(5) copies/cell, respectively. Both carry blood group Gerbich (Ge) antigens. Protein and nucleic acid analysis indicated that GPD is a truncated form of GPC in its N-terminal region and that both proteins are produced by a unique gene which is present as a single copy on chromosome 2q14-q21. GPC and GPD are produced from the same gene through use of alternative translation initiation sites. These proteins and the GYPC gene share no homology with the GPA, GPB and GPE proteins and the GYPA gene cluster, respectively. Thus, the glycophorin name, which suggests that all these sialoglycopropteins have a common genetic origin, might be now considered as a misnomer. As a further difference between the two groups of membrane proteins, GPC and GPD are expressed both in erythroid and non erythroid tissues, but the level of transcription is much higher in erythroid than in non erythroid tissues and in addition the proteins are differently glycosylated in the two cell types. Increasing evidence suggests a significant role for GPC and GPD in the regulation of the red cell shape and the membrane mechanical properties by providing a membrane linkage site for cytoskeletal proteins, especially proteins 4.1 and p55. The total lack of GPC and GPD in the red cell membrane is associated with hereditary ellyptocytosis in the Leach phenotype and the molecular basis of these defects have been elucidated.(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular basis of glycophorin C variants and their associated blood group antigens

The normal and variant forms of GPC and GPD molecules carry antigens of the Gerbich blood group system. This blood group system comprises three high-incidence antigens (Ge2, Ge3 and Ge4) and four low-incidence antigens (Wb, Lsa, Dha and Ana). Erythrocytes of the Ge and Yus phenotypes lack normal GPC and GPD molecules but express variant molecules (denoted GPC.Ge, GPC.Yus, respectively) that functionally substitute for normal GPC and GPD in the membrane. Leach phenotype cells lack GPC and GPD molecules and are elliptocytic in shape with a membrane that is less deformable than that of normal cells. The Lsa antigen is expressed on higher molecular-weight variants of GPC (GPC.Lsa) and GPD (GPD.Lsa). Wb, Dha and Ana antigens arise from point mutations in the GYPC gene and are expressed on GPC.Wb, GPC.Dha and GPD.Ana, respectively. The structure of each of the variant GPC and GPD molecules and the location of the Gerbich blood group system antigens is discussed. The GYPC gene, located on chromosome 2q14-q21, is 13.5 kb long and comprises four exons. Exons 1, 2 and most of exon 3 encode the N-terminal extracellular domain while the remainder of exon 3 and exon 4 encode transmembrane and cytoplasmic domains of GPC. Exons 2 and 3 are highly homologous, with less than 5% nucleotide divergence. The molecular basis of generation of variation GPC and GPD molecules, and the structure of the GYPC gene from different Leach phenotype individuals, is discussed.

Characterization of new murine monoclonal antibodies directed against glycophorins C and D

Six new murine monoclonal antibodies (mAbs) directed to the erythrocyte membrane glycophorins C (GPC) and D (GPD) were obtained from splenocytes of different BALB/c mice immunized with human red blood cells, and fully characterized. The mAbs were selected by agglutination tests with control and Gerbich-negative cells, and by immunoblotting analysis. They showed specificity for the N-terminal domain(s) of GPC (and GPD) and were classified into three categories by competitive analysis using 125I-labelled antibodies and real-time biospecific interaction. The first group (NaM10-7G11, NaM70-1G4 and NaM77-7B6) compete for epitope(s) located at the N-terminal portion of GPC. Agglutination-inhibition tests revealed that the 7G11 epitope involves the amino group of Met1 and sialic acid residue(s) whereas the 1G4 and 7B6 epitopes contain O-glycans. NaM89-2G11 belongs to a second group; its epitope is located in a region including Glu17, Asp19 and (an) O-glycan(s). The third group comprises mAbs NaM19-3C4 and NaM98-3C1 which bind to both GPC and GPD in proximity of the binding site of human anti-Ge:3 antibodies. In addition, mAb 3C4 (anti-GPC/GPD) was found to bind to approximately 125,000 sites per red cell. Considering that the ratio of the GPC to GPD is about 3-4 to 1, the number of GPC and GPD molecules was estimated as 95,000 and 35,000, respectively.

Blood group antigens on human erythrocytes-distribution, structure and possible functions

Human erythrocyte blood group antigens can be broadly divided into carbohydrates and proteins. The carbohydrate-dependent antigens (e.g., ABH, Lewis, Ii, P1, P-related, T and Tn) are covalently attached to proteins and/or sphingolipids, which are also widely distributed in body fluids, normal tissues and tumors. Blood group gene-specific glycosyltransferase regulate the synthesis of these antigens. Protein-dependent blood group antigens (e.g., MNSs, Gerbich, Rh, Kell, Duffy and Cromer-related) are carried on proteins, glycoproteins and proteins with glycosylphosphatidylinositol anchor. The functions of these molecules on human erythrocytes remain unknown; some of them may be involved in maintaining the erythrocyte shape. This review describes the distribution, structures and probable biological functions of some of these antigens in normal and pathological conditions.

Point mutation in the glycophorin C gene results in the expression of the blood group antigen Dha

The blood group Duch (Dha) antigen is located on glycophorin C (GPC). Total RNA prepared from the reticulocyte fraction of two Dh(a+) individuals were used in the synthesis of first-strand cDNA. The first-strand cDNA served as templates for the amplification of GPC-related DNA by polymerase chain reaction (PCR). The expected PCR product consisted of 412 base pairs. On sequencing the PCR-amplified DNA, a base change (cytosine----thymidine) at nucleotide 40 of the GPC cDNA was detected. Thus, the variant GPC (GPC.Dha) on Dh(a+) red cells has a substitution of leucine by phenylalanine at amino acid residue 14.

Human erythrocyte glycophorins: protein and gene structure analyses

Human RBCs glycophorins are integral membrane proteins rich in sialic acids that carry blood group antigenic determinants and serve as ligands for viruses, bacteria, and parasites. These molecules have long been used as a general model of membrane proteins and as markers to study normal and pathological differentiation of the erythroid tissue. The RBC glycophorins known as GPA, GPB, GPC, GPD, and GPE have recently been fully characterized at both the protein and the DNA levels, and these studies have demonstrated conclusively that these molecules can be subdivided into two groups that are distinguished by distinct properties. The first group includes the major proteins GPA and GPB, which carry the MN and Ss blood group antigens, respectively, and a recently characterized protein, GPE, presumably expressed at a low level on RBCs. All three proteins are structurally homologous and are essentially erythroid specific. The respective genes are also strikingly homologous up to a transition site defined by an Alu repeat sequence located about 1 Kb downstream from the exon encoding the transmembrane regions. Downstream of the transition site, the GPB and GPE sequences are still homologous, but diverge completely from those of GPA. The three glycophorin genes are organized in tandem on chromosome 4q28-q31, and define a small gene cluster that presumably evolved by duplication from a common ancestral gene. Most likely two sequential duplications occurred, the first, about 9 to 35 million years ago, generated a direct precursor of the GPA gene, and the second, about 5 to 21 million years ago, generated the GPB and GPE genes and that involved a gene that acquired its specific 3' end by homologous recombination through Alu repeats. Numerous variants of GPA and GPB usually detected by abnormal expression of the blood group MNSs antigens are known. An increasing number of these variants have been structurally defined by protein and molecular genetic analyses, and have been shown to result from point mutations, gene deletions, hybrid gene fusion products generated by unequal crossing-over (not at Alu repeats), and microconversion events. The second group of RBC membrane glycophorins includes the minor proteins GPC and GPD both of which carry blood group Gerbich antigens. Protein and nucleic acid analysis indicated that GPD is a truncated form of GPC in its N-terminal region, and that both proteins are produced by a unique gene called GE (Gerbich), which is present as a single copy per haploid genome and is located on chromosome 2q14-q21.(ABSTRACT TRUNCATED AT 400 WORDS)

A murine monoclonal antibody directed against the Gerbich 3 blood group antigen

A murine monoclonal antibody (NaM19-3C4, IgG1, Kappa) was produced from splenocytes of mice immunized with red blood cells. The antibody agglutinated untreated Ge:2,3,4 and Ge:-2,3,4 erythrocytes in indirect antiglobulin test but failed to agglutinate trypsin-treated cells. Gerbich-negative erythrocyte of the Leach- (Ge:-2,-3,-4) and of the Gerbich- (Ge:-2,-3,4) types were not recognized by the antibody. Immunoblotting experiments showed that the antibody bound to glycophorins C and D from control erythrocytes and to the abnormal glycophorin C identified in the Gerbich-negative cells of the Yussef type (Ge:-2,3,4). No binding to the altered glycophorin C from Ge:-2,-3,4 erythrocytes was observed, indicating that the antibody specifically recognized the Ge:3 epitope localized within residues 40-50 of glycophorin C.

Immunochemical characterisation of the low-incidence antigen, Dha

Immunoblotting with two examples of anti-Dha to the electrophoretically separated components of antigen-positive membranes gave a positive reaction with a component of the same apparent Mr (40,000) as sialoglycoprotein beta (SGP beta, syn: glycoconnectin, glycophorin C). The Dha antigenic determinant was sensitive to trypsin, but resistant to chymotrypsin and Endo F. By immunoblotting, one anti-Dha failed to react with sialidase-treated Dh(a+) cells, whilst the other gave a positive result. In contrast, neither antibody agglutinated sialidase-treated red cells. SGP beta was precipitated from Dh(a+) and Dh(a-) phenotype red cells by monoclonal anti-beta (NBTS/BRIC 10). SGP beta from Dh(a+) but not from Dh(a-) red cells was stained by immunoblotting with anti-Dha. These results assign the Dha antigenic epitope to SGP beta.

Studies on the structures of the Tm, Sj, M1, Can, Sext and Hu blood group antigens

The Glycophorins (GPs = sialoglycoproteins) in erythrocyte membranes from various Black individuals, some of which exhibit the M1, Can, Sj, Tm, Sext and/or Hu antigens, and several Caucasian donors, including pooled fetal red cells, were studied. Using agglutination inhibition assays with GP fractions, GP fragments and chemically modified GPs as well as trypsin treatment of intact red cells, the antigens defined by anti-M1, anti-M+M1, anti-Can and anti-Tm sera were found to be located on the N-terminal tryptic peptide (T2, residues 1-31) of the major GP (GP A = MN sialoglycoprotein). Evidence was obtained that the N-terminal amino-acid residue, NeuNAc and/or (a) different sugar residue(s) are involved in the antigens. Amino-acid sequence and composition analyses excluded an amino-acid exchange within the N-terminal region (residues 1-31) of GP A. Carbohydrate analyses revealed the attachment of GlcNAc residues (up to about five, dependent on the strength of the above-mentioned antigens) to O-glycosidically linked oligosaccharides within the N-terminal portion (residues 1-31) of GP A. As judged from the carbohydrate compositions of peptides, the alteration of the O-glycosidic oligosaccharides is associated with a slight increase of the Gal and Fuc contents and a slight decrease of the NeuNAc level. Analyses of small, secondary cyanogen bromide and V8 proteinase peptides from the N-terminal region of GP A from Blacks, Caucasians and Caucasian fetal cells suggest that the variable attachment of small quantities of GlcNAc (about 0.03 to about 0.2 residues per peptide molecule) accounts, at least in part, for the polymorphisms detected by anti-Can and the original anti-Tm (serum Sheerin). Remarkably, the GlcNAc-containing O-glycosidic oligosaccharides occur only in small quantities, or not all at, within the positions 32-61 of GP A and the glycosylated domains of GP B and GP C.(ABSTRACT TRUNCATED AT 400 WORDS)

Serological and immunochemical specificity of a human autoanti-Gerbich-like antibody

An 85-year-old male with cardiac failure secondary to anaemia had an apparent anti-Ge2 (Ge = Gerbich) in his serum which did not agglutinate his own red cells even though they were Ge-positive in tests with alloanti-Ge. The direct antiglobulin test was negative; however, an antibody with apparent anti-Ge2 specificity was eluted from his red cells. The patient's autoantibody was shown in immunoblotting experiments to react with an antigenic determinant on beta-sialoglycoprotein. This case illustrates that an autoanti-Ge can masquerade as an alloantibody, thereby complicating antibody identification, and implies that the immunochemical specificity of autoanti-Ge2 is different from that of alloanti-Ge2.

Blood group-active surface molecules of the human red blood cell

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) had 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 Mr 30,000, polypeptides of Mr 45,000-100,000 and Glycophorin B. The antigens of the Rh blood group system appear to be associated with the polypeptides of Mr 30,000 and those of Mr 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 Mr 30,000 and Mr 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 less than 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 Ina/Inb 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.

Structural homology between glycophorins C and D of human erythrocytes

Glycophorin C (GPC) and D (GPD) are minor glycoproteins which are believed to be important for the structural integrity of the red cell membrane. We have investigated the structural relationship between these glycoproteins by both immunological and structural investigations: 1. A rabbit anti-serum produced against GPD reacts strongly with GPC and the abnormal glycoproteins of Gerbich: -2, -3 and Gerbich: -2,3 red cells, and recognizes most probably the homologous C-terminal portions of GPC and GPD. The two molecules however differ at their N-terminus. 2. One-dimensional mapping of the peptides obtained after tryptic, chymotryptic, V8 protease or acid cleavage of 125I-labelled GPC and GPD, indicated that GPC and GPD are structurally related but some differences were found indicating that additional peptides were generated from GPC. 3. The partial primary structure of GPD was determined. The sequencing data are consistent with the assumption that GPD represents an abridged version of GPC that comprises residues approximately 21/29-128 and exhibits a N-terminal residue that is blocked by an as yet undefined group.

Rearrangements of the red-cell membrane glycophorin C (sialoglycoprotein beta) gene. A further study of alterations in the glycophorin C gene

We have cloned portions of the glycophorin C (sialoglycoprotein beta) gene from individuals with red cells of normal, Gerbich and Yus phenotypes. The clones contain up to three exons of the glycophorin C gene (designated exons 2, 3 and 4). Analysis by restriction mapping and DNA sequencing confirmed that the deletions causing the Gerbich and Yus phenotypes are located entirely within the glycophorin C gene. Sequencing of the normal gene showed that not only do exon 2 and exon 3 have related DNA sequences, but also that both the 5' and 3' flanking intronic DNA sequences are almost identical. The two variant genes each lack a different exon: the Yus type gene lacks exon 2, whereas the Gerbich-type gene lacks exon 3. We suggest that the observed deletions are due to recombination between the regions of homologous intronic repeats. We also provide evidence that an unequal cross-over mechanism may be responsible for a number of observed glycophorin C gene rearrangements, including an insertion mutation in Lewis II (Lsa)-type red cells that has not previously been reported.

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.

Genetic variants of human red-cell membrane sialoglycoprotein beta. Study of the alterations occurring in the sialoglycoprotein-beta gene

We have studied the DNA of individuals who express an altered sialoglycoprotein beta on their red cells by using Southern blotting with sialoglycoprotein-beta cDNA probes. Individuals of the Leach phenotype do not express any beta (sialoglycoprotein beta) or gamma (sialoglycoprotein gamma) on their red cells, and we show that about 7 kb of DNA, including the 3' end of the beta gene, is deleted in this DNA. Any protein product of this gene is likely to lack the membrane-associating domain of beta. We have also examined the DNA of two types of other individuals (Yus-type and Gerbich-type) who have red cells that lack beta and gamma, but contain abnormal sialoglycoproteins related to beta. These two types of DNA contain different internal deletions of about 6 kb in the beta gene. We suggest that these deletions result from the presence of two different sets of internal homology in the beta gene, and on this basis we propose structures for the abnormal Yus-type and Gerbich-type sialoglycoproteins which are consistent with the other evidence that is available. We provide evidence that beta and gamma are products of the same gene and suggest a possible mechanism for the origin of gamma based on leaky initiation of translation of beta mRNA.

Normal membrane function of abnormal beta-related erythrocyte sialoglycoproteins

Red cells totally deficient in beta and gamma sialoglycoproteins (the Leach type of Gerbich-negative) are elliptocytic and have altered membrane physical properties as evidenced by marked decreases in both membrane mechanical stability and membrane deformability. Red cells from individuals who are of the Gerbich and Yus phenotypes of Gerbich-negative are also deficient in beta and gamma sialoglycoproteins, but possess abnormal beta-related sialoglycoproteins. In order to determine if these beta-related sialoglycoproteins can functionally substitute for normal sialoglycoproteins, we measured membrane deformability and stability of red cells of the Gerbich and Yus phenotypes. In contrast to the red cells of the Leach phenotype, cells of Gerbich and Yus phenotypes were found to have normal membrane deformability and stability. Moreover, flow cytometric analysis using a monoclonal anti-beta antibody revealed that the Gerbich and Yus phenotype red cells expressed the beta-related sialoglycoprotein to the same extent as its normal counterpart on normal cells. Based on these data, we suggest that the abnormal beta-related sialoglycoproteins can functionally substitute for normal beta and gamma sialoglycoproteins.

Immunochemical characterization of the human blood cell membrane glycoprotein recognized by the monoclonal antibody 12E7

The 12E7 murine monoclonal antibody recognizes a protease-sensitive component of human red cells, platelets and lymphocytes which could not be detected on granulocytes. Scatchard analyses indicated that the 125I-labelled antibody binds to 1000, 4000 and 27,000 antigen sites on each red cell, platelet and lymphocyte respectively, with a binding constant ranging from 4 x 10(7) to 9 x 10(7) M-1. The membrane components recognized by the monoclonal antibody were characterized by immunostaining on nitrocellulose sheets. A 28 kDa sialoglycoprotein was visualized following electrophoretic transfer of the red cell and lymphocyte membrane proteins separated by SDS/polyacrylamide-gel electrophoresis. Another component of 25 kDa was also clearly identified in the lymphocyte and platelet lysates, but was barely detectable in the red cell membrane preparations. Enzyme treatment of intact platelets, as well as analysis of the membrane and cytosolic preparations from these cells, have shown that the 25 kDa component was of cytoplasmic origin. The mobility of the 28 kDa membrane component is decreased following neuraminidase treatment of intact blood cells, but these cells still react normally with the monoclonal antibody, indicating that sialic acids are not required for binding. The 28 kDa component is present on red cell membranes prepared from S-s-U-, En(a-) and Gerbich(-) individuals, demonstrating that it is a new sialoglycoprotein not derived from glycophorins A, B, C or D. The 28 kDa component was totally solubilized with 0.1% Triton X-100 from red cell membranes and behaves like the other red cell membrane sialoglycoproteins since it was extracted in the aqueous phase following chloroform/methanol/water or butanol/water partitionings. The 28 kDa component could be partially purified by h.p.l.c. gel permeation chromatography and preparative SDS/polyacrylamide-gel electrophoresis. The material finally obtained strongly inhibits the 12E7 monoclonal as well as human anti-Xga antibodies, suggesting either that the 28 kDa glycoprotein carries both antigens or that the 12E7 and Xga-active molecules copurified.

High frequency antigens of human erythrocyte membrane sialoglycoproteins, V. Characterization of the Gerbich blood group antigens: Ge2 and Ge3

The molecular properties of the major, high-frequency antigens (Ge2 and Ge3) of the human Gerbich blood group system were investigated using 14 different alloantibodies from rare Ge: -1,-2,-3 or Ge: -1,-2,3 individuals. Various modification, fractionation or fragmentation products of glycophorins (sialoglycoproteins) from normal erythrocytes (phenotype Ge: 1,2,3) were used in hemagglutination inhibition assays. The location of the antigens was also studied by blotting of proteins, separated by dodecyl sulfate polyacrylamide gel electrophoresis, to nitrocellulose and detection of bound antibodies by 125I-labelled protein G. Anti-Ge3 was found to be directed against a region of glycophorin C that surrounds a tryptic cleavage site at position 48 and a similar region of glycophorin D whose structure is not yet known. NeuAc residue(s), probably representing part(s) of a carbohydrate unit attached to serine42 of glycophorin C, methionine, aspartic or glutamic acid, tryptophan and/or arginine residue(s) are involved in the Ge3 epitopes, as judged from chemical modification. The Ge2 epitopes were found to be located on a tryptic glycopeptide from glycophorin D comprising about 20-30 amino-acid residues. NeuAc residue(s), attached to serine-/threonine-linked oligosaccharide(s), are involved in the Ge2 determinants. Using the immunoblotting technique, it could also be shown that the 'new' glycophorin in Ge: -1,-2,3 cells carries the Ge3 antigen.

Hybrid glycophorins from human erythrocyte membranes. Isolation and complete structural analysis of the novel sialoglycoprotein from St(a+) red cells

Human red cells from donor Pj carry the Sta blood group antigen and an unusual sialoglycoprotein of 24 kDa molecular mass tentatively identified as a hybrid molecule of the anti-Lepore type [Blanchard et al. (1982) Biochem. J. 203, 419-426]. This component is resistant towards proteinase treatment and was purified from trypsin-treated and chymotrypsin-treated Pj erythrocytes. The molecule is composed of 99 amino acid residues whose alignment was established following manual and automatic sequencing of cyanogen bromide, trypsin, chymotrypsin and V8 proteinase peptides. The polypeptide chain comprises residues 1-26/28 of glycophorin B and residues 59/61-131 of glycophorin A. The sugar composition resembles that of glycophorin B, indicating the absence of an N-glycosidic chain. Identical sequences were obtained from analyses of the 24-kDa component purified from unrelated St(a+) donors. These results support the hypothesis that glycoprotein Pj represents a B-A hybrid molecule which is encoded by a new gene product resulting from an unequal crossing-over between the genes coding for the polypeptide chains of the glycophorins A and B. The novel molecule carries both N and Sta blood group antigens. The N activity is clearly understandable from the sequence of the five N-terminal residues (Leu and Glu at positions 1 and 5 respectively). Inhibition studies with the untreated and chemically modified hybrid glycoprotein indicate that the Sta determinant is located within residues approximately 25-30 of the molecule, which corresponds to the newly formed sequence found neither in glycophorin A nor in glycophorin B.

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.

The Dantu erythrocyte phenotype of the NE variety. I. Dodecylsulfate polyacrylamide gel electrophoretic studies

Red cell membranes from patient NE, Mr. Dantu and 16 additional Black individuals, positive for the low-frequency MNSs-system antigen Dantu, were studied by dodecylsulfate polyacrylamide gel electrophoretic techniques. The content of the major, blood group M- or N-active sialoglycoprotein (glycophorin A, GP A) was found to be decreased by about 57%. The blood group S- or s-active sialoglycoprotein (GP B) was decreased by about 51% in membranes from proven Dantu/U heterozygotes and not detectable in those from patient NE and other Dantu+U- individuals. Donor NE was shown to exhibit the genotype Dantu/u. Dantu-positive cells exhibit a proteinase-resistant GP B-GP A hybrid with an apparent molecular mass of 29 KDa whose intramembraneous and cytoplasmic domains were shown to be similar to those of GP A. The molar hybrid: GP A ratio in all cells was found to be about 2.4: 1, indicating that the NE variety of the Dantu phenotype is much more frequent than the Ph or MD types. The significance of an additional minor 'new' component (molecular mass 21 KDa) in Dantu+ membranes and the minor component J (molecular mass 22 KDa) occurring in normal and Dantu+U+ GP preparations, but not in those from Dantu+U- cells, has not been resolved. The apparent molecular mass of the anion channel protein (band 3) in all cells of the NE variety was shown to be decreased by about 3 KDa, due to a shortening of carbohydrate chains. This suggests that the hybrid, just like GP A, might form a complex with band 3.

The Dantu erythrocyte phenotype of the NE variety. II. Serology, immunochemistry, genetics, and frequency

Red cells (RBC) possessing the low-frequency MNSs antigen Dantu from 36 Black individuals (21 propositi) were found to exhibit the NE variety of this phenotype, as judged from the electrophoretic glycophorin (GP) pattern, described in an accompanying article, and/or from the polybrene test which detects the decreased NeuAc level of these RBC. All known DantuNE RBC (53) exhibit the phenotype M+N+. This finding as well as family studies and immunochemical investigations demonstrate that the DantuNE allele encodes a blood group M-specific GP A. Thus, the strongly decreased GP A level of RBC from DantuNE heterozygotes represents the product of the Dantu allele and its normal counterpart. It is suggested that the formation of a complex with the anion channel protein (band 3) represents the prerequisite for optimum incorporation of GP A into normal RBC membranes. The hybrid GP in DantuNE RBC, produced in large quantity, might suppress the incorporation of GP A in a cis and trans manner via the formation of a complex with band 3. The hybrid GP in DantuNE RBC lacks U activity, but expresses N activity and a qualitatively altered s antigen, thus proving its GP B-GP A hybrid nature in conjunction with data described in the accompanying article. Screening of ficin-treated RBC with Vicia lectin revealed that the Dantu phenotype exhibits a frequency of about 0.005 in American Blacks and less than 0.001 in Germans.

Hybrid glycophorins from human erythrocyte membranes. I. Isolation and complete structural analysis of the hybrid sialoglycoprotein from Dantu-positive red cells of the N.E. variety

The hybrid glycophorin in Dantu-positive human erythrocytes of the N.E. variety was not cleaved by treatment of intact cells with various proteases, in contrast to normal glycophorins. Therefore, it could be purified by phenol/saline extraction of membranes from trypsin-treated and chymotrypsin-treated red cells and subsequent gel filtration in the presence of Ammonyx-LO. The complete structure of the hybrid molecule, comprising 99 amino acid residues, was elucidated by sequence analyses of peptides prepared by chymotrypsin, trypsin, cyanogen bromide or V8 proteinase treatment. The N-terminal 39 residues and the glycosylation of the molecule were found to be indistinguishable from those of blood-group-s-specific glycophorin B. Conversely, the residues 39-99 were shown to be identical with the residues 71-131 of the major blood-group M-active or N-active sialoglycoprotein (glycophorin A). Hemagglutination inhibition assays revealed that the Dantu antigen represents a labile structure. The receptor might be located within the residues approximately 28-40 of the hybrid glycophorin, as judged from the effects of modifications of membranes. Our data provide an explanation for the previous findings that Dantu-positive cells (N.E. type) exhibit a protease-resistant N antigen and a qualitatively altered s antigen.

Gerbich blood group deficiency of the Ge:-1,-2,-3 and Ge:-1,-2,3 types. Immunochemical study and genomic analysis with cDNA probes

Human erythrocytes carry several transmembrane glycoproteins, among which the two minor species associated with the blood group Gerbich (Ge) antigens, GP C and GP D, play pivotal role since they interact with the membrane cytoskeleton and contribute to maintain the normal red cell shape. On the red cells from two categories of homozygous donors lacking the Ge determinants (Ge:-1,-2,-3 and Ge:-1,-2,3), GP C and GP D are missing but instead there is a new glycoprotein, easily detected by SDS/polyacrylamide gel electrophoresis, which exhibits some properties shared by GP C and GP D. This was shown by immunochemical analyses with a murine monoclonal antibody, extraction of the glycoproteins by organic solvents and binding studies with the 125I-labelled Lens culinaris lectin. The red cells from obligate heterozygotes for the Ge:-1,-2,-3 condition also carry this new glycoprotein component but in a much lesser amount than expected on the basis of one gene dose response. Using a cDNA probe containing the coding sequence of human GP C and the entire 3' untranslated region of its mRNA, we have demonstrated by Southern analyses that the Ge:-1,-2,-3 and the Ge:-1,-2,3 conditions are associated with a constant 3-kbp deletion within the GP C gene. Similar studies indicated that this gene is present as a unique copy per haploid genome of Ge-positive control donors (Ge:1,2,3). To account for these data and for the glycoprotein profile of Ge-negative erythrocytes, it is proposed that a unique Gerbich gene encodes for GP C and GP D, either by alternative RNA splicing or by different post-translational events, and that, following a 3-kbp deletion within this gene, a new glycoprotein having properties common to GP C and GP D can be produced.

Instability of red cell shape associated with the absence of membrane glycophorin C

Erythrocytes from 3 Gerbich-negative siblings readily converted to echinocytes when subjected to changing concentrations of sodium or lithium chloride. When erythrocyte membrane proteins were assayed by immunoblotting with human anti-Ge 1,2, normal membranes were found to contain a reactive component of an approximate molecular weight of 33,000 daltons which was absent from the Gerbich-negative individuals. PAS staining and mobility on SDS gels identified this component as glycophorin C. These observations indicate that glycophorin C (beta-sialoglycoprotein) is a component of the Gerbich antigen and is involved in normal cell shape maintenance.

Toxic effect of isolated glycophorin A on the in vitro growth of Plasmodium falciparum

We have examined the inhibitory potencies of glycophorin A, a mixture of glycophorins B and C, chymotryptic fragments of GpA, desialylated GpA, alkaliborohydride treated GpA, and the O-linked tetrasaccharide isolated from GpA on the invasion of human red blood cells by synchronous Plasmodium falciparum (strain FCB). 50% inhibition of invasion, as measured by 3H-hypoxanthine incorporation into parasites, was achieved at 14 and 155 microM for GpA and GpA-CH1, respectively. We have noticed, however, that isolated GpA exhibits a toxic effect on the intraerythrocytic growth of the parasite whereas the chymotryptic fragment (amino acid residues 1-64 of GpA) does not. Thus the inhibitory potency of isolated GpA during erythrocyte invasion by the merozoite should be regarded as the result of both an inhibitory and a toxic effect. The inhibitory effect should be attributed to the carbohydrate-rich outer portion of GpA carrying clusters of neuraminic acid. The toxic effect should be attributed to the hydrophobic region of GpA which might be capable of inserting into the membrane of free merozoites and/or erythrocytes. Our data suggest that results previously obtained with glycoprotein inhibitors carrying hydrophobic portions may have to be questioned.

Gerbich reactivity in 4.1 (-) hereditary elliptocytosis and protein 4.1 level in blood group Gerbich deficiency

The membrane polypeptide composition and the blood group Gerbich phenotype of red cells from 4.1 (-) hereditary elliptocytic patients and from Gerbich-negative donors, who display two unrelated genetic abnormalities, were compared. In homozygous 4.1 (-) hereditary elliptocytosis where the primary defect was presumably the absence of the membrane skeletal protein 4.1, there was approximatively a 70% reduction in the minor sialoglycoproteins beta and gamma. This was associated with a severe reduction of blood group Gerbich reactivity as determined with both murine monoclonal and human anti-Gerbich antibodies. In the heterozygous state in the presence of one haploid set of protein 4.1 gene there was only a modest decrease in glycoproteins beta and gamma and the Gerbich serological reactivity was within normal limits. In homozygous Gerbich-negative red cells which lack glycoproteins beta and gamma but do not display elliptocytic red cells, the levels of protein 4.1 was repeatedly found within or just below the lowest values of normal controls. In the heterozygous Gerbich-negative conditions, glycoproteins beta and gamma were present in reduced amounts but the blood group Gerbich reactivity fell within normal limits since the anti-Gerbich reagents used were unable to detect a dosage effect. The amount of protein 4.1 was normal. These results add further support to the view that protein 4.1 and the sialoglycoproteins beta and gamma are physically linked in vivo which in some way serve to maintain red cell shape and integrity. Of interest was the finding that absence of protein 4.1 had a greater influence on the level of membrane glycoproteins beta and gamma than did the absence of beta and gamma glycoproteins on band 4.1.

Localization of the gene for human erythrocyte glycophorin C to chromosome 2, q14-q21

A complementary cDNA clone (900 bp) representing the 3' untranslated region and almost the entire coding sequence of the human erythrocyte membrane glycophorin C has been used to determine the chromosomal location of the blood group Gerbich locus by in situ hybridization. The results indicate that this locus is assigned to the region q14-q21 of chromosome 2.

A human monoclonal IgM kappa cold agglutinin recognizing oligosaccharides with immunodominant sialyl groups preferentially at the blood group M-specific peptide backbone of glycophorins: anti-PrM

A kappa-monotypic IgM high titer cold agglutinin reacting like anti-Pr at low, like anti-M at higher temperatures, is described. It recognizes tetra- and/or trisaccharides with immunodominant sialyl groups on glycophorins A, B, C like anti-Pr. Its affinity to the oligosaccharides is, however, approximately 10-fold increased when they are attached to the M-specific peptide backbone of glycophorin A. The antibody, termed anti-PrM, occurred in a blood group MN patient with chronic cold agglutinin disease and caused autoimmune hemolytic anemia.

High frequency antigens of human erythrocyte membrane sialoglycoproteins, III. Studies on the EnaFR, Wrb and Wra antigens

The nature of the common erythrocyte antigens EnaFR and Wrb, that are both absent from En(a-) cells, and the rare Wra receptor, apparently encoded by an allele of Wrb, was investigated. Various modification, fractionation or cleavage products of erythrocyte membranes were used in hemagglutination inhibition assays. The EnaFR and Wrb antigens were shown to represent labile structures within the residues approx. 62-72 of the major (MN) sialoglycoprotein that require lipids, at least for complete expression of antigenic activity. During the course of these experiments, the arrangement of the MN glycoprotein's peptide chain with respect to the lipid bi-layer was also studied, using various proteinases. Furthermore, the MN glycoprotein was found to aggregate with the major membrane protein (band 3) in the presence of Triton X-100. The Wra antigen was shown to exhibit properties that differ considerably from those of the Wrb receptor. Analyses on the MN glycoprotein, isolated from the red cells of the only known Wra homozygote and two WraWrb individuals, did not reveal any amino-acid exchange within the residues 40-96 of the molecule. Therefore, the Wr locus that determines the presence or absence of the Wrb antigen on the MN glycoprotein might influence the post-translational modification of amino-acid residues, the structure of tightly bound lipids or the aggregation of the MN glycoprotein with a different protein such as band 3.

The inheritance of abnormal sialoglycoproteins found in a Gerbich negative individual

The Gerbich blood group antigens are probably expressed on one or more of the minor erythrocyte (beta, beta 1, or gamma) sialoglycoproteins which are lacking in some rare individuals having the Gerbich negative phenotype. A monoclonal antibody, CMRF-10, which recognises a trypsin-sensitive site on both the beta and beta 1 sialoglycoproteins, was tested for binding to erythrocytes from a Gerbich negative individual, OM. Erythrocytes from OM bound CMRF-10 in similar amounts to normal erythrocytes even though membranes from OM were shown by sodium dodecyl sulphate-polyacrylamide gel electrophoresis to lack both the beta and gamma sialoglycoproteins found in normal red blood cells. Instead, abnormal sialoglycoproteins which migrated as two bands with apparent molecular weights within the range 29,500-32,500 daltons were identified and purified using CMRF-10. Subsequent electrophoretic analysis of OM's two children failed to reveal any abnormal sialoglycoproteins. This suggests that in this instance the Gerbich negative phenotype may result from other mechanisms, possibly defective glycosylation, rather than a crossover involving the gene coding for the primary protein structure of the sialoglycoproteins.