title: Mutagenesis analysis of the rGTP-specific binding site of hepatitis C virus RNA-dependent RNA polymerase.
abstract: Hepatitis C virus (HCV) nonstructural protein 5B (NS5B) is the virus-encoded RNA-dependent RNA polymerase (RdRp) essential for HCV RNA replication. An earlier crystallographic study identified a rGTP-specific binding site lying at the surface between the thumb domain and the fingertip about 30 A away from the active site of the HCV RdRp (S. Bressanelli, L. Tomei, F. A. Rey, and R. De Francesco, J. Virol 76:3482-3492, 2002). To determine its physiological importance, we performed a systematic mutagenesis analysis of the rGTP-specific binding pocket by amino acid substitutions. Effects of mutations of the rGTP-specific binding site on enzymatic activity were determined by an in vitro RdRp assay, while effects of mutations on HCV RNA replication were examined by cell colony formation, as well as by transient replication of subgenomic HCV RNAs. Results derived from these studies demonstrate that amino acid substitutions of the rGTP-specific binding pocket did not significantly affect the in vitro RdRp activity of purified recombinant NS5B proteins, as measured by their abilities to synthesize RNA on an RNA template containing the 3' untranslated region of HCV negative-strand RNA. However, most mutations of the rGTP-specific binding site either impaired or completely ablated the ability of subgenomic HCV RNAs to induce cell colony formation. Likewise, these mutations caused either reduction in or lethality to transient replication of the human immunodeficiency virus Tat-expressing HCV replicon RNAs in the cell. Collectively, these findings demonstrate that the rGTP-specific binding site of the HCV NS5B is not required for in vitro RdRp activity but is important for HCV RNA replication in vivo.
authors.affiliation: Department of Microbiology, Immunology, and Molecular Genetics, University of Kentucky College of Medicine, 800 Rose St., MN477, Lexington, KY 40536-0298, USA.
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Cai
authors.forename: MinKyung
authors.initials: M
authors.lastname: Yi
authors.forename: Chen
authors.initials: C
authors.lastname: Zhang
authors.forename: Guangxiang
authors.initials: G
authors.lastname: Luo
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001483:Base Sequence; D020134:Catalytic Domain / Q000235:genetics; D002460:Cell Line; D004279:DNA, Viral / Q000235:genetics; D006160:Guanosine Triphosphate / Q000378:metabolism*; D016174:Hepacivirus / Q000201:enzymology* / Q000235:genetics* / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D012367:RNA, Viral / Q000096:biosynthesis / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017361:Viral Nonstructural Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D014779:Virus Replication / Q000235:genetics / Q000502:physiology; D012324:RNA-Dependent RNA Polymerase
chemical_list: D004279:DNA, Viral; D006160:Guanosine Triphosphate; D012367:RNA, Viral; D011994:Recombinant Proteins; D017361:Viral Nonstructural Proteins; C087036:NS-5 protein, hepatitis C virus; D012324:RNA-Dependent RNA Polymerase