One-step immunopurification and lectinochemical characterization of the Duffy atypical chemokine receptor from human erythrocytes

Duffy antigen/receptor for chemokines (DARC) is a glycosylated seven-transmembrane protein acting as a blood group antigen, a chemokine binding protein and a receptor for Plasmodium vivax malaria parasite. It is present on erythrocytes and endothelial cells of postcapillary venules. The N-terminal extracellular domain of the Duffy glycoprotein carries Fya/Fyb blood group antigens and Fy6 linear epitope recognized by monoclonal antibodies. Previously, we have shown that recombinant Duffy protein expressed in K562 cells has three N-linked oligosaccharide chains, which are mainly of complex-type. Here we report a one-step purification method of Duffy protein from human erythrocytes. DARC was extracted from erythrocyte membranes in the presence of 1% n-dodecyl-β-D-maltoside (DDM) and 0.05% cholesteryl hemisuccinate (CHS) and purified by affinity chromatography using immobilized anti-Fy6 2C3 mouse monoclonal antibody. Duffy glycoprotein was eluted from the column with synthetic DFEDVWN peptide containing epitope for 2C3 monoclonal antibody. In this single-step immunoaffinity purification method we obtained highly purified DARC, which migrates in SDS-polyacrylamide gel as a major diffuse band corresponding to a molecular mass of 40–47 kDa. In ELISA purified Duffy glycoprotein binds anti-Duffy antibodies recognizing epitopes located on distinct regions of the molecule. Results of circular dichroism measurement indicate that purified DARC has a high content of α-helical secondary structure typical for chemokine receptors. Analysis of DARC glycans performed by means of lectin blotting and glycosidase digestion suggests that native Duffy N-glycans are mostly triantennary complex-type, terminated with α2-3- and α2-6-linked sialic acid residues with bisecting GlcNAc and α1-6-linked fucose at the core

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

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66122/1/j.1432-1033.1984.tb08155.x.pd

Receptor and ligand domains for invasion of erythrocytes by Plasmodium falciparum

A 175-kilodalton erythrocyte binding protein, EBA-175, of the parasite Plasmodium falciparum mediates the invasion of erythrocytes. The erythrocyte receptor for EBA-175 is dependent on sialic acid. The domain of EBA-175 that binds erythrocytes was identified as region II with the use of truncated portions of EBA-175 expressed on COS cells. Region II, which contains a cysteine-rich motif, and native EBA-175 bind specifically to glycophorin A, but not to glycophorin B, on the erythrocyte membrane. Erythrocyte recognition of EBA-175 requires both sialic acid and the peptide backbone of glycophorin A. The identification of both the receptor and ligand domains may suggest rational designs for receptor blockade and vaccines

Complex trend of magnetic order in Fe clusters on 4d transition-metal surfaces. I. Experimental evidence and Monte Carlo simulations

We demonstrate the occurrence of compensated spin configurations in Fe clusters and monolayers on Ru(0001) and Rh(111) by a combination of x-ray magnetic circular dichroism experiments, first-principles calculations, and Monte Carlo simulations. Our results reveal complex intracluster exchange interactions which depend strongly on the substrate 4d-band filling, the cluster geometry, as well as lateral and vertical structural relaxations. The importance of substrate 4d-band filling manifests itself also in small nearest-neighbor exchange interactions in Fe dimers and in a nearly inverted trend of the Ruderman-Kittel-Kasuya-Yosida coupling constants for Fe adatoms on the Ru and Rh surface

Identification of an Erythrocyte Binding Peptide from the Erythrocyte Binding Antigen, EBA-175, Which Blocks Parasite Multiplication and Induces Peptide-Blocking Antibodies

A biotinylated peptide covering a sequence of 21 amino acids (aa) from the erythrocyte binding antigen (EBA-175) of Plasmodium falciparum bound to human glycophorin A, an erythrocyte receptor for merozoites, as demonstrated by enzyme-linked immunosorbent assay (ELISA) and to erythrocytes as demonstrated by flow cytometry analysis. The peptide, EBA(aa1076–96), also bound to desialylated glycophorin A and glycophorin B when tested by ELISA. The peptide blocked parasite multiplication in vitro. The glycophorin A binding sequence was further delineated to a 12-aa sequence, EBA(aa1085–96), by testing the binding of a range of truncated peptides to immobilized glycophorin A. Our data indicate that EBA(aa1085–96) is part of a ligand on the merozoite for binding to erythrocyte receptors. This binding suggests that the EBA(aa1085–96) peptide is involved in a second binding step, independent of sialic acid. Antibody recognition of this peptide sequence may protect against merozoite invasion, but only a small proportion of sera from adults from different areas of malaria transmission showed antibody reactivities to the EBA(aa1076–96) peptide, indicating that this sequence is only weakly immunogenic during P. falciparum infections in humans. However, Tanzanian children with acute clinical malaria showed high immunoglobulin G reactivity to the EBA(aa1076–96) peptide compared to children with asymptomatic P. falciparum infections. The EBA(aa1076–96) peptide sequence from EBA-175 induced antibody formation in mice after conjugation of the peptide with purified protein derivative. These murine sera inhibited EBA(aa1076–96) peptide binding to glycophorin A

Studies of a murine monoclonal antibody directed against DARC: reappraisal of its specificity.

Duffy Antigen Receptor for Chemokines (DARC) plays multiple roles in human health as a blood group antigen, a receptor for chemokines and the only known receptor for Plasmodium vivax merozoites. It is the target of the murine anti-Fy6 monoclonal antibody 2C3 which binds to the first extracellular domain (ECD1), but exact nature of the recognized epitope was a subject of contradictory reports. Here, using a set of complex experiments which include expression of DARC with amino acid substitutions within the Fy6 epitope in E. coli and K562 cells, ELISA, surface plasmon resonance (SPR) and flow cytometry, we have resolved discrepancies between previously published reports and show that the basic epitope recognized by 2C3 antibody is 22FEDVW26, with 22F and 26W being the most important residues. In addition, we demonstrated that 30Y plays an auxiliary role in binding, particularly when the residue is sulfated. The STD-NMR studies performed using 2C3-derived Fab and synthetic peptide corroborated most of these results, and together with the molecular modelling suggested that 25V is not involved in direct interactions with the antibody, but determines folding of the epitope backbone