title: The baboon erythrocyte complement receptor is a glycophosphatidylinositol-linked protein encoded by a homologue of the human CR1-like genetic element.
abstract: The human erythrocyte CA receptor (E-CR) is the type 1 complement receptor (CR1), the most common form of which is a 220,000 Mr integral membrane glycoprotein composed of 30 short consensus repeats (SCRs). The E-CR of many nonhuman primates is a smaller receptor of unknown genetic origin. Recently, we identified a chimp cDNA, termed CR1b, which represented transcription of a homologue of the human genetic element, CR1-like. The purpose of this study was to identify CR1b in the baboon and, if present, determine whether it encodes the 65,000 Mr baboon E-CR. Baboon bone marrow cDNA was amplified by PCR using primers specific for the signal peptide-encoding region of human CR1 and the 3' region of chimp CR1b. This amplification yielded a CR1b sequence predicted to encode seven SCRs followed by a hydrophobic region, with an N terminus homologous to the N terminus of baboon E-CR. Expression of baboon CR1b yielded a membrane protein that reacted with an anti-CR1 mAb, was identical in size to baboon E-CR, and, like baboon E-CR, could bind baboon C3 linked to activated thiol-Sepharose (C3i-ATS), but not human C3i-ATS. Phosphatidylinositol-specific phospholipase C (PIPLC) released CR1b from Chinese hamster ovary cells and E-CR from baboon erythrocytes, demonstrating that both of these proteins are glycophosphatidylinositol linked to the membrane. Thus, the data indicate that baboon CR1b, a homologue of the human CR1-like genetic element, encodes a glycophosphatidylinositol-linked protein that is the baboon E-CR.
authors.affiliation: Department of Internal Medicine, The Ohio State University, Columbus 43210, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Birmingham
authors.forename: C M
authors.initials: CM
authors.lastname: Logar
authors.forename: X P
authors.initials: XP
authors.lastname: Shen
authors.forename: W
authors.initials: W
authors.lastname: Chen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D018076:DNA, Complementary / Q000302:isolation & purification; D004912:Erythrocytes / Q000276:immunology* / Q000378:metabolism; D017261:Glycosylphosphatidylinositols / Q000097:blood / Q000737:chemistry / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D002679:Pan troglodytes; D010215:Papio / Q000235:genetics* / Q000276:immunology*; D017463:Receptors, Complement 3b / Q000097:blood / Q000737:chemistry* / Q000235:genetics*; D017386:Sequence Homology, Amino Acid
chemical_list: D018076:DNA, Complementary; D017261:Glycosylphosphatidylinositols; D017463:Receptors, Complement 3b