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

Recombinant forms of Gerbich blood group antigens: expression and purification

Recombinant forms of normal glycophorin C (GPC), carrying the high frequency Gerbich blood group antigens, and its natural deletion mutants of Yus and Ge type (all combined with oligohistidyl tag) were expressed in CHO and COS 7 cells. The stable expression of all recombinant forms of GPC in CHO cells was obtained, but the level of expression was low and detectable only by flow cytometry. The high level of transient expression of GPC recombinant forms in COS 7 cells allowed their purification on Ni-NTA-agarose. The purified recombinant GPC and mutants of Yus and Ge type behaved in SDS-PAGE similarly to normal GPC forms from RBC membranes. The recombinant GPC.Yus and GPC.Ge mutants appeared as diffuse bands, suggesting the similar heterogeneity of glycosylation that was observed in natural GPC.Yus and GPC.Ge glycoproteins. The flow cytometry analysis of the transfected CHO and COS 7 cells showed that binding of anti-GPC monoclonal antibodies to GPC variants was accordant with the known fine specificity of these antibodies. The obtained recombinant forms of GPC carrying common Gerbich antigens may be useful in serology, and also as model molecules for structure-function studies.

Recombinant forms of glycophorin C as a tool for characterization of epitopes for new murine monoclonal antibodies with anti-glycophorin C specificity

Glycophorin C (GPC) and glycophorin D (GPD) are minor but important components of human RBC membranes. They carry the high-frequency antigens Ge2, Ge3 and Ge4 of the Gerbich blood group system. The epitopes for five new monoclonal antibodies (MoAbs) with anti-GPC specificity were characterized. Two antibodies (4G11 and 5B11) reacted with glycosylated N-terminal epitopes, and three reacted with internal epitopes of GPC. Pepscan analysis showed that the MoAb RB11 required for binding the EPDP sequence, occurring twice in GPC polypeptide chain. The MoAb 7F11 recognized the sequence 13PLSLEPDP20, and the MoAb RB8 did not react with synthetic peptides. Further characterization of the internal epitopes was performed in fluorescence-activated cell sorter (FACS) with the use of recombinant GPC and its variant forms transiently expressed on COS-7 cells. The results indicated that the MoAb RB11 recognized distinctly its target sequence EPDP only in a normal GPC molecule. The reactivity of the MoAb 7F11 with the PLSLEPDP sequence was confirmed and found to be enhanced by the O-glycan at the Ser15 residue. The MoAb RB8 recognized the glycopeptidic epitope in proximity to the Ser15 residue, requiring the presence of O-glycan. The combination of immunochemical techniques with the use of the recombinant forms of GPC has made it possible to define the role of sugar chains in the recognition of peptidic epitopes in glycosylated antigen and sheds new light on the Gerbich system antigens.

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.

Reactivity with erythroid and non-erythroid tissues of a murine monoclonal antibody to a synthetic peptide having amino acid sequence common to cytoplasmic domain of human glycophorins C and D

Three synthetic peptides encompassing the entire cytoplasmic polypeptide sequence (amino acid residues 82-128) of glycophorin C (GPC) and glycophorin D (GPD) were used to immunize mice for the production of monoclonal antibodies (MoAbs). Only the synthetic peptide (GPC-peptide-1) corresponding to C-terminal residues 112-128 elicited a MoAb (named BGRL-100) which could react with native and denatured GPC and GPD. We characterized BGRL-100 by inhibition using GPC-peptide 1 and red cell sialoglycoproteins. The ability of BGRL-100 to interact with native GPC and GPD was assessed by immunoprecipitation with normal red cells (RBCs), and with denatured GPC and GPD by Western blotting of both normal RBCs and RBCs carrying GPC variants. Immunohistochemical staining of human tissue sections was performed using both BGRL-100 and a rat MoAb (named BRAC-1), which is specific for an extracellular domain of GPC and GPD. Both antibodies showed strong staining of erythroid lineage haemopoietic cells in fetal liver, sinusoids of adult liver and RBCs in the blood vessels of all tissues tested. Neither antibody reacted with epithelia from a range of human tissues. However, both MoAbs stained neural tissue in a distinctive fibrillar pattern. This suggests the presence of an analogue of erythroid GPC in neural tissues.

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.

Degradation of human erythrocyte surface components by human neutrophil elastase and cathepsin G: preferential digestion of glycophorins

Human erythrocytes treated with purified human neutrophil elastase (HNE) or cathepsin G (CathG) were analysed by serological methods and by SDS-polyacrylamide gel electrophoresis followed by staining or immunoblotting with monoclonal antibodies. Both enzymes digested exhaustively glycophorins A, B and C, and HNE caused a partial digestion of band 3 protein. The degradation of other membrane proteins was not detectable by the methods used. Immunoblotting with the use of monoclonal antibodies against the defined epitopes of glycophorin A showed that HNE and CathG hydrolysed distinct peptide bonds in this antigen. The antibody PEP80, specific for the epitope in the cytoplasmic fragment of glycophorin A, gave patterns of bands which were characteristic for each of the two proteases. These bands could be distinctly identified in erythrocyte membrane samples containing only few percent of digested glycophorins. Therefore, the immunoblotting with this antibody may be useful as a sensitive assay for detecting the action of neutrophil proteases on red blood cells.

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.

Distinction of the glycophorin C locus from the Diego, Dombrock and Yt blood group loci

DNA samples from families informative for the Diego (DI), Dombrock (DO) and Yt (YT) blood group loci were analyzed with a cDNA probe defining a Taq I polymorphism at the glycophorin C locus (GYPC). Recombination between GYPC and DI, DO and YT occurs. Hence GYPC is differentiated from all established blood group system loci.

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.

The Mz variety of the St(a+) phenotype--a variant of glycophorin A exhibiting a deletion

The NeuNAc level of erythrocyte membranes from two related donors exhibiting the Mz variety of St(a+) phenotype within the MNSs blood group system was found to be decreased by about 16%. The quantity of glycophorin A was decreased by about 38%, whereas that of glycophorin B was not significantly different from normal. Mz erythrocyte membranes were also found to contain an abnormal component (molar ratio to glycophorin A about 0.89:1.0) with an apparent molecular mass of about 24,000 Da. Immunoblotting experiments and amino-acid sequence analysis revealed that the novel component (and glycophorin A in one of the donors) carries blood group M activity. Blood group N activity was demonstrable for glycophorin A and glycophorin B from both donors. Amino-acid sequence analysis of chymotryptic, tryptic and cyanogen bromide peptides demonstrated that the novel molecule exhibits the typical structure of a Sta-active molecule. However, since it exhibits blood group M activity, it appears to represent a variant of glycophorin A lacking the residues 27-58 (encoded by exon three of the glycophorin A gene) rather than a glycophorin B-glycophorin A-hybrid molecule of the anti-Lepore type. Since one of the Mz heterozygotes was found to exhibit both M- and N activity on glycophorin A, the Mz gene complex appears to encode a blood group N-active glycophorin A apart from the novel component and a blood group s-active glycophorin B, although the level of glycophorin A in the erythrocyte membranes is decreased by about half.(ABSTRACT TRUNCATED AT 250 WORDS)

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.