The C terminus of hepatitis C virus NS4A encodes an electrostatic switch that regulates NS5A hyperphosphorylation and viral replication.
Hepatitis C virus (HCV) nonstructural protein 4A (NS4A) is only 54 amino acids (aa) in length, yet it is a key regulator of the essential serine protease and RNA helicase activities of the NS3-4A complex, as well as a determinant of NS5A phosphorylation. Here we examine the structure and function of the C-terminal acidic region of NS4A through site-directed mutagenesis of a Con1 subgenomic replicon and through biophysical characterization of a synthetic peptide corresponding to this region. Our genetic studies revealed that in 8 of the 15 C-terminal residues of NS4A, individual Ala substitutions or charge reversal substitutions led to severe replication phenotypes, as well as decreased NS5A hyperphosphorylation. By selecting for replication-competent mutants, several second-site changes in NS3 were identified and shown to suppress these defects in replication and NS5A hyperphosphorylation. Circular-dichroism spectroscopy and nuclear magnetic resonance spectroscopy on a peptide corresponding to the C-terminal 19 aa of NS4A revealed that this region can adopt an alpha-helical conformation, but that this folding requires neutralization of a cluster of acidic residues. Taken together, these data suggest that the C terminus of NS4A acts as a dynamic regulator of NS3-4A interaction, NS5A hyperphosphorylation, and HCV replicase activity.
Lindenbach
Brett D
BD
Center for the Study of Hepatitis C, The Rockefeller University, New York, NY 10021, USA. brett.lindenbach@yale.edu
Prágai
Béla M
BM
Montserret
Roland
R
Beran
Rudolf K F
RK
Pyle
Anna M
AM
Penin
François
F
Rice
Charles M
CM
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D045744:Cell Line, Tumor; D002942:Circular Dichroism; D004252:DNA Mutational Analysis; D016174:Hepacivirus / Q000235:genetics / Q000502:physiology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D017510:Protein Folding; D025941:Protein Interaction Mapping; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013489:Suppression, Genetic; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D014779:Virus Replication / Q000235:genetics / Q000502:physiology*; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases; D012324:RNA-Dependent RNA Polymerase
D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D017361:Viral Nonstructural Proteins; D014764:Viral Proteins; C084422:NS3 protein, hepatitis C virus; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases; C455041:NS4A cofactor peptide, Hepatitis C virus; C087036:NS-5 protein, hepatitis C virus; D012324:RNA-Dependent RNA Polymerase