A short peptide at the amino terminus of the Sendai virus C protein acts as an independent element that induces STAT1 instability.
The Sendai virus C protein acts to dismantle the interferon-induced cellular antiviral state in an MG132-sensitive manner, in part by inducing STAT1 instability. This activity of C maps to the first 23 amino acids (C(1-23)) of the 204-amino-acid (aa)-long protein (C(1-204)). C(1-23) was found to act as an independent viral element that induces STAT1 instability, since this peptide fused to green fluorescent protein (C(1-23)/GFP) is at least as active as C(1-204) in this respect. This peptide also induces the degradation of C(1-23)/GFP and other proteins to which it is fused. Most of C(1-204), and particularly its amino-terminal half, is predicted to be structurally disordered. C(1-23) as a peptide was found to be disordered by circular dichroism, and the first 11 aa have a strong potential to form an amphipathic alpha-helix in low concentrations of trifluoroethanol, which is thought to mimic protein-protein interaction. The critical degradation-determining sequence of C(1-23) was mapped by mutation to eight residues near its N terminus: (4)FLKKILKL(11). All the large hydrophobic residues of (4)FLKKILKL(11), plus its ability to form an amphipathic alpha-helix, were found to be critical for STAT1 degradation. In contrast, C(1-23)/GFP self-degradation did not require (8)ILKL(11), nor the ability to form an alpha-helix throughout this region. Remarkably, C(1-23)/GFP also stimulated C(1-204) degradation, and this degradation in trans required the same peptide determinants as for STAT1. Our results suggest that C(1-204) coordinates its dual activities of regulating viral RNA synthesis and counteracting the host innate antiviral response by sensing both its own intracellular concentration and that of STAT1.
Garcin
Dominique
D
Department of Microbiology and Molecular Medicine, University of Geneva School of Medicine, 11 Ave. de Champel, CH1211 Geneva, Switzerland.
Marq
Jean-Baptiste
JB
Iseni
Fréderic
F
Martin
Stephen
S
Kolakofsky
Daniel
D
D000595:Amino Acid Sequence; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005786:Gene Expression Regulation; D049452:Green Fluorescent Proteins; D006801:Humans; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010455:Peptides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017510:Protein Folding; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D050794:STAT1 Transcription Factor; D029082:Sendai virus / Q000472:pathogenicity*; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D015534:Trans-Activators / Q000378:metabolism*; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D004268:DNA-Binding Proteins; D008164:Luminescent Proteins; D010455:Peptides; D011993:Recombinant Fusion Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D015534:Trans-Activators; D014764:Viral Proteins; C051221:nonstructural C protein, Sendai virus; D049452:Green Fluorescent Proteins