title: Hydrodynamic, electron microscopic, and ligand-binding analysis of the Epstein-Barr virus/C3dg receptor (CR2).
abstract: The interaction of the Epstein-Barr virus/45-kDa proteolytic fragment of C3 (C3dg) receptor (CR2) with its viral ligand, the Epstein-Barr virus glycoprotein gp350/220, initiates the sequence of events leading to virus internalization and B lymphocyte transformation. Soluble recombinant receptor (rCR2) and gp350/220 as well as the natural ligand, C3dg, were subjected to a number of analytical techniques including gel permeation chromatography, density gradient ultracentrifugation, circular dichroism, and electron microscopy in order to determine their hydrodynamic, structural, and binding properties. Both rCR2 and gp350/220 were found to be highly extended proteins (f/fo = 2.1 and 2.4/2.2, respectively). C3dg, in contrast to the viral ligand, is only somewhat elongated (f/fo = 1.5). Soluble rCR2, visualized by high resolution electron microscopy, was shown to be an extended, highly flexible molecule comprised of ringlet domains, each approximately 24.1 A in length, which likely correspond to the short consensus repeat motif deduced from the CR2 cDNA nucleotide sequence. Ligand-binding studies carried out under physiological conditions indicated that gp350/220 binding to rCR2 was saturable and univalent, with a dissociation constant of 3.2 nM. In contrast, monomeric C3dg did not bind to rCR2 under physiological conditions; however, at reduced ionic strength, monomeric C3dg binding could be measured. These studies indicate that the affinity of the C3dg monomer for rCR2 under physiologic conditions is approximately 10(4)-fold less than that of the viral ligand. The molecular properties of rCR2 revealed in these studies provide essential information for future studies of the biologic functions of the Epstein-Barr virus/C3dg receptor.
authors.affiliation: Department of Immunology, Research Institute of Scripps Clinic, La Jolla, California 92037.
authors.forename: M D
authors.initials: MD
authors.lastname: Moore
authors.forename: R G
authors.initials: RG
authors.lastname: DiScipio
authors.forename: N R
authors.initials: NR
authors.lastname: Cooper
authors.forename: G R
authors.initials: GR
authors.lastname: Nemerow
mesh_terms: D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte / Q000378:metabolism; D000956:Antigens, Viral / Q000378:metabolism*; D002942:Circular Dichroism; D015933:Complement C3d / Q000378:metabolism* / Q000648:ultrastructure; D004797:Enzyme-Linked Immunosorbent Assay; D004854:Herpesvirus 4, Human / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D007700:Kinetics; D008024:Ligands; D008854:Microscopy, Electron; D011485:Protein Binding; D011487:Protein Conformation; D011951:Receptors, Complement / Q000378:metabolism*; D017464:Receptors, Complement 3d; D014763:Viral Matrix Proteins
chemical_list: D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; D000956:Antigens, Viral; C037662:EBV-associated membrane antigen, Epstein-Barr virus; D008024:Ligands; D011951:Receptors, Complement; D017464:Receptors, Complement 3d; D014763:Viral Matrix Proteins; D015933:Complement C3d