2a4g

Structural highlights

Function

POLG_HCV1 Packages viral RNA to form a viral nucleocapsid, and promotes virion budding (Probable). Participates in the viral particle production as a result of its interaction with the non-structural protein 5A (By similarity). Binds RNA and may function as a RNA chaperone to induce the RNA structural rearrangements taking place during virus replication (By similarity). Modulates viral translation initiation by interacting with viral IRES and 40S ribosomal subunit (By similarity). Affects various cell signaling pathways, host immunity and lipid metabolism (Probable). Prevents the establishment of cellular antiviral state by blocking the interferon-alpha/beta (IFN-alpha/beta) and IFN-gamma signaling pathways and by blocking the formation of phosphorylated STAT1 and promoting ubiquitin-mediated proteasome-dependent degradation of STAT1 (By similarity). Activates STAT3 leading to cellular transformation (By similarity). Regulates the activity of cellular genes, including c-myc and c-fos (PubMed:8533458). May repress the promoter of p53, and sequester CREB3 and SP110 isoform 3/Sp110b in the cytoplasm (PubMed:9110985). Represses cell cycle negative regulating factor CDKN1A, thereby interrupting an important check point of normal cell cycle regulation (PubMed:9524287). Targets transcription factors involved in the regulation of inflammatory responses and in the immune response: suppresses TNF-induced NF-kappa-B activation, and activates AP-1 (PubMed:9811706). Binds to dendritic cells (DCs) via C1QR1, resulting in down-regulation of T-lymphocytes proliferation (By similarity). Alters lipid metabolism by interacting with hepatocellular proteins involved in lipid accumulation and storage (By similarity). Induces up-regulation of FAS promoter activity, and thereby contributes to the increased triglyceride accumulation in hepatocytes (steatosis) (By similarity).[UniProtKB:P26662][UniProtKB:P27958][UniProtKB:P29846][UniProtKB:Q99IB8]^{[1] [2] [3] [4]} Forms a heterodimer with envelope glycoprotein E2, which mediates virus attachment to the host cell, virion internalization through clathrin-dependent endocytosis and fusion with host membrane (By similarity). Fusion with the host cell is most likely mediated by both E1 and E2, through conformational rearrangements of the heterodimer required for fusion rather than a classical class II fusion mechanism (By similarity). E1/E2 heterodimer binds host apolipoproteins such as APOB and APOE thereby forming a lipo-viro-particle (LVP) (By similarity). APOE associated to the LVP allows the initial virus attachment to cell surface receptors such as the heparan sulfate proteoglycans (HSPGs), syndecan-1 (SDC1), syndecan-1 (SDC2), the low-density lipoprotein receptor (LDLR) and scavenger receptor class B type I (SCARB1) (By similarity). The cholesterol transfer activity of SCARB1 allows E2 exposure and binding of E2 to SCARB1 and the tetraspanin CD81 (By similarity). E1/E2 heterodimer binding on CD81 activates the epithelial growth factor receptor (EGFR) signaling pathway (By similarity). Diffusion of the complex E1-E2-EGFR-SCARB1-CD81 to the cell lateral membrane allows further interaction with Claudin 1 (CLDN1) and occludin (OCLN) to finally trigger HCV entry (By similarity).[UniProtKB:P27958] Forms a heterodimer with envelope glycoprotein E1, which mediates virus attachment to the host cell, virion internalization through clathrin-dependent endocytosis and fusion with host membrane (By similarity). Fusion with the host cell is most likely mediated by both E1 and E2, through conformational rearrangements of the heterodimer required for fusion rather than a classical class II fusion mechanism (By similarity). The interaction between envelope glycoprotein E2 and host apolipoprotein E/APOE allows the proper assembly, maturation and infectivity of the viral particles (By similarity). This interaction is probably promoted via the up-regulation of cellular autophagy by the virus (By similarity). E1/E2 heterodimer binds host apolipoproteins such as APOB and APOE thereby forming a lipo-viro-particle (LVP) (By similarity). APOE associated to the LVP allows the initial virus attachment to cell surface receptors such as the heparan sulfate proteoglycans (HSPGs), syndecan-1 (SDC1), syndecan-1 (SDC2), the low-density lipoprotein receptor (LDLR) and scavenger receptor class B type I (SCARB1) (By similarity). The cholesterol transfer activity of SCARB1 allows E2 exposure and binding of E2 to SCARB1 and the tetraspanin CD81 (By similarity). E1/E2 heterodimer binding on CD81 activates the epithelial growth factor receptor (EGFR) signaling pathway (By similarity). Diffusion of the complex E1-E2-EGFR-SCARB1-CD81 to the cell lateral membrane allows further interaction with Claudin 1 (CLDN1) and occludin (OCLN) to finally trigger HCV entry (By similarity). Inhibits host EIF2AK2/PKR activation, preventing the establishment of an antiviral state (PubMed:10390359, PubMed:11152499). 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 (By similarity). These interactions allow the capture of circulating HCV particles by these cells and subsequent facilitated transmission to permissive cells such as hepatocytes and lymphocyte subpopulations (By similarity). The interaction between E2 and host amino acid transporter complex formed by SLC3A2 and SLC7A5/LAT1 may facilitate viral entry into host cell (By similarity).[UniProtKB:P27958]^{[5] [6]} Ion channel protein that acts as a viroporin and plays an essential role in the assembly, envelopment and secretion of viral particles (By similarity). Regulates the host cell secretory pathway, which induces the intracellular retention of viral glycoproteins and favors assembly of viral particles (By similarity). Creates a pore in acidic organelles and releases Ca(2+) and H(+) in the cytoplasm of infected cells, leading to a productive viral infection (By similarity). High levels of cytoplasmic Ca(2+) may trigger membrane trafficking and transport of viral ER-associated proteins to viroplasms, sites of viral genome replication (Probable). This ionic imbalance induces the assembly of the inflammasome complex, which triggers the maturation of pro-IL-1beta into IL-1beta through the action of caspase-1 (By similarity). Targets also host mitochondria and induces mitochondrial depolarization (By similarity). In addition of its role as a viroporin, acts as a lipid raft adhesion factor (By similarity).[UniProtKB:P26662][UniProtKB:P27958][UniProtKB:Q99IB8] Cysteine protease required for the proteolytic auto-cleavage between the non-structural proteins NS2 and NS3 (By similarity). The N-terminus of NS3 is required for the function of NS2 protease (active region NS2-3) (By similarity). Promotes the initiation of viral particle assembly by mediating the interaction between structural and non-structural proteins (By similarity).[UniProtKB:P26663][UniProtKB:P27958][UniProtKB:Q99IB8] Displays three enzymatic activities: serine protease with a chymotrypsin-like fold, NTPase and RNA helicase (By similarity). NS3 serine protease, in association with NS4A, is responsible for the cleavages of NS3-NS4A, NS4A-NS4B, NS4B-NS5A and NS5A-NS5B (By similarity). The NS3/NS4A complex prevents phosphorylation of host IRF3, thus preventing the establishment of dsRNA induced antiviral state (By similarity). The NS3/NS4A complex induces host amino acid transporter component SLC3A2, thus contributing to HCV propagation (By similarity). NS3 RNA helicase binds to RNA and unwinds both dsDNA and dsRNA in the 3' to 5' direction, and likely resolves RNA complicated stable secondary structures in the template strand (By similarity). Binds a single ATP and catalyzes the unzipping of a single base pair of dsRNA (By similarity). Inhibits host antiviral proteins TBK1 and IRF3 thereby preventing the establishment of an antiviral state (By similarity). Cleaves host MAVS/CARDIF thereby preventing the establishment of an antiviral state (By similarity). Cleaves host TICAM1/TRIF, thereby disrupting TLR3 signaling and preventing the establishment of an antiviral state (By similarity).[UniProtKB:P27958][UniProtKB:Q9WMX2] The NS3/NS4A complex prevents phosphorylation of host IRF3, thus preventing the establishment of dsRNA induced antiviral state (By similarity). The NS3/NS4A complex induces host amino acid transporter component SLC3A2, thus contributing to HCV propagation (By similarity).[UniProtKB:P27958][UniProtKB:Q9WMX2] Induces a specific membrane alteration that serves as a scaffold for the virus replication complex (By similarity). This membrane alteration gives rise to the so-called ER-derived membranous web that contains the replication complex (By similarity). NS4B self-interaction contributes to its function in membranous web formation (By similarity). Promotes host TRIF protein degradation in a CASP8-dependent manner thereby inhibiting host TLR3-mediated interferon signaling (By similarity). Disrupts the interaction between STING and TBK1 contributing to the inhibition of interferon signaling (By similarity).[UniProtKB:P27958] Phosphorylated protein that is indispensable for viral replication and assembly (By similarity). Both hypo- and hyperphosphorylated states are required for the viral life cycle (By similarity). The hyperphosphorylated form of NS5A is an inhibitor of viral replication (By similarity). Involved in RNA-binding and especially in binding to the viral genome (By similarity). Zinc is essential for RNA-binding (By similarity). Participates in the viral particle production as a result of its interaction with the mature viral core protein (By similarity). Its interaction with host VAPB may target the viral replication complex to vesicles (By similarity). Down-regulates viral IRES translation initiation (PubMed:15784895). Mediates interferon resistance, presumably by interacting with and inhibiting host EIF2AK2/PKR (PubMed:9143277). Prevents BIN1-induced apoptosis (By similarity). Acts as a transcriptional activator of some host genes important for viral replication when localized in the nucleus (By similarity). Via the interaction with host PACSIN2, modulates lipid droplet formation in order to promote virion assembly (By similarity). Modulates TNFRSF21/DR6 signaling pathway for viral propagation (By similarity).[UniProtKB:P26662][UniProtKB:P27958][UniProtKB:Q99IB8][UniProtKB:Q9WMX2]^{[7] [8]} RNA-dependent RNA polymerase that performs primer-template recognition and RNA synthesis during viral replication.[UniProtKB:P27958]

See Also

• Helicase 3D structures
• Virus protease 3D structures

References

1. ↑ Ray RB, Lagging LM, Meyer K, Steele R, Ray R. Transcriptional regulation of cellular and viral promoters by the hepatitis C virus core protein. Virus Res. 1995 Aug;37(3):209-20. PMID:8533458 doi:10.1016/0168-1702(95)00034-n
2. ↑ Ray RB, Steele R, Meyer K, Ray R. Transcriptional repression of p53 promoter by hepatitis C virus core protein. J Biol Chem. 1997 Apr 25;272(17):10983-6. PMID:9110985 doi:10.1074/jbc.272.17.10983
3. ↑ Ray RB, Steele R, Meyer K, Ray R. Hepatitis C virus core protein represses p21WAF1/Cip1/Sid1 promoter activity. Gene. 1998 Feb 27;208(2):331-6. PMID:9524287 doi:10.1016/s0378-1119(98)00030-4
4. ↑ Shrivastava A, Manna SK, Ray R, Aggarwal BB. Ectopic expression of hepatitis C virus core protein differentially regulates nuclear transcription factors. J Virol. 1998 Dec;72(12):9722-8. PMID:9811706 doi:10.1128/JVI.72.12.9722-9728.1998
5. ↑ Taylor DR, Shi ST, Romano PR, Barber GN, Lai MM. Inhibition of the interferon-inducible protein kinase PKR by HCV E2 protein. Science. 1999 Jul 2;285(5424):107-10. PMID:10390359 doi:10.1126/science.285.5424.107
6. ↑ Taylor DR, Tian B, Romano PR, Hinnebusch AG, Lai MM, Mathews MB. Hepatitis C virus envelope protein E2 does not inhibit PKR by simple competition with autophosphorylation sites in the RNA-binding domain. J Virol. 2001 Feb;75(3):1265-73. PMID:11152499 doi:10.1128/JVI.75.3.1265-1273.2001
7. ↑ Kalliampakou KI, Kalamvoki M, Mavromara P. Hepatitis C virus (HCV) NS5A protein downregulates HCV IRES-dependent translation. J Gen Virol. 2005 Apr;86(Pt 4):1015-1025. PMID:15784895 doi:10.1099/vir.0.80728-0
8. ↑ Gale MJ Jr, Korth MJ, Tang NM, Tan SL, Hopkins DA, Dever TE, Polyak SJ, Gretch DR, Katze MG. Evidence that hepatitis C virus resistance to interferon is mediated through repression of the PKR protein kinase by the nonstructural 5A protein. Virology. 1997 Apr 14;230(2):217-27. PMID:9143277 doi:10.1006/viro.1997.8493
9. ↑ Arasappan A, Njoroge FG, Chan TY, Bennett F, Bogen SL, Chen K, Gu H, Hong L, Jao E, Liu YT, Lovey RG, Parekh T, Pike RE, Pinto P, Santhanam B, Venkatraman S, Vaccaro H, Wang H, Yang X, Zhu Z, Mckittrick B, Saksena AK, Girijavallabhan V, Pichardo J, Butkiewicz N, Ingram R, Malcolm B, Prongay A, Yao N, Marten B, Madison V, Kemp S, Levy O, Lim-Wilby M, Tamura S, Ganguly AK. Hepatitis C virus NS3-4A serine protease inhibitors: SAR of P'2 moiety with improved potency. Bioorg Med Chem Lett. 2005 Oct 1;15(19):4180-4. PMID:16087332 doi:10.1016/j.bmcl.2005.06.091