title: The Cys-rich region of hepatitis A virus cellular receptor 1 is required for binding of hepatitis A virus and protective monoclonal antibody 190/4.
abstract: The hepatitis A virus cellular receptor 1 (HAVcr-1) cDNA codes for a class I integral membrane glycoprotein, termed havcr-1, of unknown natural function which serves as an African green monkey kidney (AGMK) cell receptor for HAV. The extracellular domain of havcr-1 has an N-terminal Cys-rich region that displays homology with sequences of members of the immunoglobulin superfamily, followed by a Thr/Ser/Pro (TSP)-rich region characteristic of mucin-like O-glycosylated proteins. The havcr-1 glycoprotein contains four putative N-glycosylation sites, two in the Cys-rich region and two in the TSP-rich region. To characterize havcr-1 and define region(s) involved in HAV receptor function, we expressed the TSP-rich region in Escherichia coli fused to glutathione S-transferase and generated antibodies (Ab) in rabbits (anti-GST2 Ab). Western blot analysis with anti-GST2 Ab detected 62- and 65-kDa bands in AGMK cells and 59-, 62-, and 65-kDa bands in dog cells transfected with the HAVcr-1 cDNA (cr5 cells) but not in dog cells transfected with the vector alone (DR2 cells). Treatment of AGMK and cr5 cell extracts with peptide-N-glycosidase F resulted in the collapse of the havcr-1-specific bands into a single band of 56 kDa, which indicated that different N-glycosylated forms of havcr-1 were expressed in these cells. Treatment of AGMK and cr5 cells with tunicamycin reduced binding of protective monoclonal Ab (MAb) 190/4, which suggested that N-glycans are required for binding of MAb 190/4 to havcr-1. To test this hypothesis, havcr-1 mutants lacking the N-glycosylation motif at the first site (mut1), second site (mut2), and both (mut3) sites were constructed and transfected into dog cells. Binding of MAb 190/4 and HAV to mut1 and mut3 cells was highly reduced, while binding to mut2 cells was not affected and binding to dog cells expressing an havcr-1 construct containing a deletion of the Cys-rich region (d1- cells) was undetectable. HAV-infected cr5 and mut2 cells but not mut1, mut3, d1-, and DR2 cells developed the characteristic cytoplasmic granular fluorescence of HAV-infected cells. These results indicate that the Cys-rich region of havcr-1 and its first N-glycosylation site are required for binding of protective MAb 190/4 and HAV receptor function.
authors.affiliation: Laboratory of Hepatitis Viruses, Division of Viral Products, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20892, USA.
authors.forename: P
authors.initials: P
authors.lastname: Thompson
authors.forename: J
authors.initials: J
authors.lastname: Lu
authors.forename: G G
authors.initials: GG
authors.lastname: Kaplan
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism*; D001483:Base Sequence; D002460:Cell Line; D002522:Chlorocebus aethiops; D003545:Cysteine / Q000235:genetics / Q000378:metabolism*; D004285:Dogs; D006031:Glycosylation; D000072596:Hepatitis A Virus Cellular Receptor 1; D006507:Hepatovirus / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009841:Oligonucleotides; D011817:Rabbits; D011991:Receptors, Virus / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; C491143:HAVCR1 protein, human; D000072596:Hepatitis A Virus Cellular Receptor 1; D008562:Membrane Glycoproteins; D009841:Oligonucleotides; D011991:Receptors, Virus; D003545:Cysteine