title: Identification of amino acid residues important for heparan sulfate proteoglycan interaction within variable region 3 of the feline immunodeficiency virus surface glycoprotein.
abstract: Heparan sulfate proteoglycans (HSPGs) act as binding receptors or attachment factors for the viral envelope of many viruses, including strains of HIV and feline immunodeficiency virus (FIV). The FIV gp95 glycoprotein (SU) from laboratory-adapted strains (tissue culture adapted [TCA]) such as FIV-34TF10 can bind to HSPG, whereas SU from field strains (FS) such as FIV-PPR cannot. Previous studies indicate that SU-HSPG interactions occur within the V3 loop. We utilized a series of nested V3 peptides to further map the HSPG binding sites and found that both sides of the predicted V3 loop stem were critical for the binding but not the CXCR4 binding domain near the predicted tip of the V3 loop. Neutralization assays for TCA strain entry using the same set of V3 peptides showed that peptides targeting CXCR4 or HSPG binding sites can block infection, supporting the V3 loop as a critical neutralization target. Site-directed mutagenesis identified two highly conserved arginines, R379 and R389, on the N-terminal side of the V3 stem as critical for the contact between SU and HSPG. Residues K407, K409, K410, and K412 on the C-terminal side of the V3 stem form a second nonconserved domain necessary for HSPG binding, consistent with the observed specificity distinctions with FS FIV. Our findings discriminate structural determinants important for HSPG and CXCR4 binding by FIV SU and thus further define the importance of the V3 loop for virus entry and infection.
authors.affiliation: Department of Immunology and Microbial Science, The Scripps Research Institute, 10550 North Torrey Pines Road, MB-14, La Jolla, CA 92037, USA.
authors.forename: Qiong-Ying
authors.initials: QY
authors.lastname: Hu
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Fink
authors.forename: Meaghan
authors.initials: M
authors.lastname: Happer
authors.forename: John H
authors.initials: JH
authors.lastname: Elder
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D002415:Cats; D002460:Cell Line; D017931:DNA Primers; D005434:Flow Cytometry; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019812:Heparan Sulfate Proteoglycans / Q000378:metabolism*; D016089:Immunodeficiency Virus, Feline / Q000378:metabolism* / Q000502:physiology; D008561:Membrane Fusion; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D019718:Receptors, CXCR4 / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D017931:DNA Primers; D006023:Glycoproteins; D019812:Heparan Sulfate Proteoglycans; D019718:Receptors, CXCR4; D014759:Viral Envelope Proteins