2jy0
Solution NMR structure of HCV NS2 protein, membrane segment (1-27)
Structural highlights
FunctionPOLG_HCVCO 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).[1] [2] 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).[3] [4] 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).[5] [6] Protease NS2-3 is a cysteine protease responsible for the autocatalytic cleavage of NS2-NS3. Seems to undergo self-inactivation following maturation (By similarity).[7] [8] 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.[9] [10] 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).[11] [12] 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).[13] [14] NS5B is a RNA-dependent RNA polymerase that plays an essential role in the virus replication (By similarity).[15] [16] Publication Abstract from PubMedThe hepatitis C virus (HCV) is a flavivirus replicating in the cytoplasm of infected cells. The HCV genome is a single stranded RNA encoding a polyprotein cleaved by cellular and viral proteases into 10 products. While the structural proteins core, envelope protein 1 (E1) and E2 build up the virus particle, most nonstructural (NS) proteins are required for RNA replication. One of the least studied proteins is NS2, which is composed of a C-terminal cytosolic protease domain and a highly hydrophobic N-terminal domain. It is assumed that the latter is composed of 3 trans-membrane segments (TMS) that tightly attach NS2 to intracellular membranes. Taking advantage of a system to study HCV assembly in a hepatoma cell line, in this study we performed a detailed characterization of NS2 with respect to its role for particle assembly. In agreement with an earlier report (Jones et al., J Virol, 81, 8374-8383, 2007) we demonstrate that the protease domain, but not its enzymatic activity is required for infectious virus production. We also show that serine 168 in NS2 implicated in phosphorylation and stability of this protein is dispensable for virion formation. Furthermore, we determined the NMR structure of the first TMS of NS2 and show that the N-terminal segment (aa 3 to 11) forms a putative flexible helical element connected to a stable alpha-helix (aa 12 to 21) that includes an absolutely conserved helix side in genotype 1b. By using this structure and the amino acid conservation as a guide for a functional study, we determined the contribution of individual amino acid residues in TMS1 for HCV assembly. We identified several residues that are critical for virion formation, most notably a central glycine residue at position 10 of TMS1. Finally, we demonstrate that mutations in NS2 blocking HCV assembly can be rescued by trans-complementation. Structural and functional characterization of non-structural protein 2 for its role in hepatitis C virus assembly.,Jirasko V, Montserret R, Appel N, Janvier A, Eustachi L, Brohm C, Steinmann E, Pietschmann T, Penin F, Bartenschlager R J Biol Chem. 2008 Jul 21. PMID:18644781[17] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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