title: A Point Mutation in the N-Terminal Amphipathic Helix α0in NS3 Promotes Hepatitis C Virus Assembly by Altering Core Localization to the Endoplasmic Reticulum and Facilitating Virus Budding.
abstract: The assembly of hepatitis C virus (HCV), a complicated process in which many viral and cellular factors are involved, has not been thoroughly deciphered. NS3 is a multifunctional protein that contains an N-terminal amphipathic α helix (designated helix α0), which is crucial for the membrane association and stability of NS3 protein, followed by a serine protease domain and a C-terminal helicase/NTPase domain. NS3 participates in HCV assembly likely through its C-terminal helicase domain, in which all reported adaptive mutations enhancing virion assembly reside. In this study, we determined that the N-terminal helix α0of NS3 may contribute to HCV assembly. We identified a single mutation from methionine to threonine at amino acid position 21 (M21T) in helix α0, which significantly promoted viral production while having no apparent effect on the membrane association and protease activity of NS3. Subsequent analyses demonstrated that the M21T mutation did not affect HCV genome replication but rather promoted virion assembly. Further study revealed a shift in the subcellular localization of core protein from lipid droplets (LD) to the endoplasmic reticulum (ER). Finally, we showed that the M21T mutation increased the colocalization of core proteins and viral envelope proteins, leading to a more efficient envelopment of viral nucleocapsids. Collectively, the results of our study revealed a new function of NS3 helix α0and aid understanding of the role of NS3 in HCV virion morphogenesis.IMPORTANCEHCV NS3 protein possesses the protease activity in its N-terminal domain and the helicase activity in its C-terminal domain. The role of NS3 in virus assembly has been mainly attributed to its helicase domain, because all adaptive mutations enhancing progeny virus production are found to be within this domain. Our study identified, for the first time to our knowledge, an adaptive mutation within the N-terminal helix α0domain of NS3 that significantly enhanced virus assembly while having no effect on viral genome replication. The mechanistic studies suggested that this mutation promoted the relocation of core proteins from LD to the ER, leading to a more efficient envelopment of viral nucleocapsids. Our results revealed a possible new function of helix α0in the HCV life cycle and provided new clues to understanding the molecular mechanisms for the action of NS3 in HCV assembly.
authors.affiliation: Unit of Viral Hepatitis, CAS Key Laboratory of Molecular Virology & Immunology, Institut Pasteur of Shanghai, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, People's Republic of China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Yan
authors.affiliation: Unit of Viral Hepatitis, CAS Key Laboratory of Molecular Virology & Immunology, Institut Pasteur of Shanghai, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, People's Republic of China.
authors.forename: Ying
authors.initials: Y
authors.lastname: He
authors.affiliation: CIRI-International Center for Infectiology Research, Team EVIR, Inserm, U1111, Université Claude Bernard Lyon 1, CNRS, UMR5308, Ecole Normale Supérieure de Lyon, Université de Lyon, Lyon, France.
authors.forename: Bertrand
authors.initials: B
authors.lastname: Boson
authors.affiliation: Unit of Viral Hepatitis, CAS Key Laboratory of Molecular Virology & Immunology, Institut Pasteur of Shanghai, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, People's Republic of China.
authors.forename: Xuesong
authors.initials: X
authors.lastname: Wang
authors.affiliation: CIRI-International Center for Infectiology Research, Team EVIR, Inserm, U1111, Université Claude Bernard Lyon 1, CNRS, UMR5308, Ecole Normale Supérieure de Lyon, Université de Lyon, Lyon, France.
authors.forename: François-Loïc
authors.initials: FL
authors.lastname: Cosset
authors.affiliation: Unit of Viral Hepatitis, CAS Key Laboratory of Molecular Virology & Immunology, Institut Pasteur of Shanghai, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, People's Republic of China jzhong@sibs.ac.cn.
authors.forename: Jin
authors.initials: J
authors.lastname: Zhong
mesh_terms: D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000821:virology*; D016174:Hepacivirus / Q000235:genetics / Q000502:physiology*; D022781:Hepatocytes / Q000821:virology; D006801:Humans; D008715:Methionine / Q000235:genetics / Q000378:metabolism; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D017354:Point Mutation; D013912:Threonine / Q000235:genetics / Q000378:metabolism; D014758:Viral Core Proteins / Q000378:metabolism*; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000378:metabolism*; D019065:Virus Assembly; D057074:Virus Release; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases
chemical_list: D008715:Methionine; D050505:Mutant Proteins; D013912:Threonine; D014758:Viral Core Proteins; D017361:Viral Nonstructural Proteins; C084422:NS3 protein, hepatitis C virus; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases; C069130:nucleocapsid protein, Hepatitis C virus
keywords: HCV; NS3; assembly; core; helix α0; hepatitis C virus