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HCV-J6 NS5B polymerase structure at 1.8 Angstrom
Structural highlights
FunctionPOLG_HCVJ6 Core protein packages viral RNA to form a viral nucleocapsid, and promotes virion budding. Modulates viral translation initiation by interacting with HCV IRES and 40S ribosomal subunit. Also regulates many host cellular functions such as signaling pathways and apoptosis. Prevents the establishment of cellular antiviral state by blocking the interferon-alpha/beta (IFN-alpha/beta) and IFN-gamma signaling pathways and by inducing human STAT1 degradation. Thought to play a role in virus-mediated cell transformation leading to hepatocellular carcinomas. Interacts with, and activates STAT3 leading to cellular transformation. May repress the promoter of p53, and sequester CREB3 and SP110 isoform 3/Sp110b in the cytoplasm. Also represses cell cycle negative regulating factor CDKN1A, thereby interrupting an important check point of normal cell cycle regulation. Targets transcription factors involved in the regulation of inflammatory responses and in the immune response: suppresses NK-kappaB activation, and activates AP-1. Could mediate apoptotic pathways through association with TNF-type receptors TNFRSF1A and LTBR, although its effect on death receptor-induced apoptosis remains controversial. Enhances TRAIL mediated apoptosis, suggesting that it might play a role in immune-mediated liver cell injury. Seric core protein is able to bind C1QR1 at the T-cell surface, resulting in down-regulation of T-lymphocytes proliferation. May transactivate human MYC, Rous sarcoma virus LTR, and SV40 promoters. May suppress the human FOS and HIV-1 LTR activity. Alters lipid metabolism by interacting with hepatocellular proteins involved in lipid accumulation and storage. Core protein induces up-regulation of FAS promoter activity, and thereby probably contributes to the increased triglyceride accumulation in hepatocytes (steatosis) (By similarity). E1 and E2 glycoproteins form a heterodimer that is involved in virus attachment to the host cell, virion internalization through clathrin-dependent endocytosis and fusion with host membrane. E1/E2 heterodimer binds to human LDLR, CD81 and SCARB1/SR-BI receptors, but this binding is not sufficient for infection, some additional liver specific cofactors may be needed. The fusion function may possibly be carried by E1. E2 inhibits human EIF2AK2/PKR activation, preventing the establishment of an antiviral state. E2 is a viral ligand for CD209/DC-SIGN and CLEC4M/DC-SIGNR, which are respectively found on dendritic cells (DCs), and on liver sinusoidal endothelial cells and macrophage-like cells of lymph node sinuses. These interactions allow capture of circulating HCV particles by these cells and subsequent transmission to permissive cells. DCs act as sentinels in various tissues where they entrap pathogens and convey them to local lymphoid tissue or lymph node for establishment of immunity. Capture of circulating HCV particles by these SIGN+ cells may facilitate virus infection of proximal hepatocytes and lymphocyte subpopulations and may be essential for the establishment of persistent infection (By similarity). P7 seems to be a heptameric ion channel protein (viroporin) and is inhibited by the antiviral drug amantadine. Also inhibited by long-alkyl-chain iminosugar derivatives. Essential for infectivity (By similarity). Protease NS2-3 is a cysteine protease responsible for the autocatalytic cleavage of NS2-NS3. Seems to undergo self-inactivation following maturation (By similarity). NS3 displays three enzymatic activities: serine protease, NTPase and RNA helicase. NS3 serine protease, in association with NS4A, is responsible for the cleavages of NS3-NS4A, NS4A-NS4B, NS4B-NS5A and NS5A-NS5B. NS3 RNA helicase binds to RNA and unwinds dsRNA in the 3' to 5' direction, and likely RNA stable secondary structure in the template strand. Cleaves the host antiviral protein MAVS (By similarity). NS3/NS4A complex also prevents phosphorylation of human IRF3, thus preventing the establishment of dsRNA induced antiviral state. NS4B induces a specific membrane alteration that serves as a scaffold for the virus replication complex. This membrane alteration gives rise to the so-called ER-derived membranous web that contains the replication complex (By similarity). NS5A is a component of the replication complex involved in RNA-binding. Its interaction with Human VAPB may target the viral replication complex to vesicles. Down-regulates viral IRES translation initiation. Mediates interferon resistance, presumably by interacting with and inhibiting human EIF2AK2/PKR. Seems to inhibit apoptosis by interacting with BIN1 and FKBP8. The hyperphosphorylated form of NS5A is an inhibitor of viral replication (By similarity). NS5B is an RNA-dependent RNA polymerase that plays an essential role in the virus replication (By similarity). Publication Abstract from PubMedThe HCV genotype 2a isolate JFH1 represents the only cloned HCV wild-type sequence capable of efficient replication in cell culture as well as in vivo. Previous reports have pointed to NS5B, the viral RNA dependent RNA polymerase (RdRp), as a major determinant for efficient replication of this isolate. To understand the contribution of the JFH1 NS5B gene at the molecular level, we aimed at conferring JFH1 properties to NS5B from the closely related J6 isolate. We created intragenotypic chimeras in the NS5B region of JFH1 and J6 and compared replication efficiency in cell culture and RdRp activity of the purified proteins in vitro, revealing more than three independent mechanisms conferring the role of JFH1 NS5B in efficient RNA replication. Most critical was residue I405 in the thumb domain of the polymerase, strongly stimulating replication in cell culture by enhancing overall de novo RNA synthesis. A structural comparison of JFH1 and J6 at high resolution indicated a clear correlation of a closed thumb conformation of the RdRp and the efficiency of the enzyme at de novo RNA synthesis, in accordance with the proposal that I405 enhances de novo initiation. In addition, we identified several residues enhancing replication independent of RdRp activity in vitro. The functional properties of JFH1 NS5B could be restored by a few single nucleotide substitutions to the J6 isolate. Finally, we were able to enhance replication efficiency of a genotype 1b isolate with the I405 mutation, indicating that this mechanism of action is conserved across genotypes. A comprehensive structure-function comparison of hepatitis C virus strains JFH1 and J6 polymerases reveals a key residue stimulating replication in cell culture across genotypes.,Schmitt M, Scrima N, Radujkovic D, Caillet-Saguy C, Simister PC, Friebe P, Wicht O, Klein R, Bartenschlager R, Lohmann V, Bressanelli S J Virol. 2011 Jan 5. PMID:21209117[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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