title: The hypervariable amino-terminus of P1 protease modulates potyviral replication and host defense responses.
abstract: The replication of many RNA viruses involves the translation of polyproteins, whose processing by endopeptidases is a critical step for the release of functional subunits. P1 is the first protease encoded in plant potyvirus genomes; once activated by an as-yet-unknown host factor, it acts in cis on its own C-terminal end, hydrolyzing the P1-HCPro junction. Earlier research suggests that P1 cooperates with HCPro to inhibit host RNA silencing defenses. Using Plum pox virus as a model, we show that although P1 does not have a major direct role in RNA silencing suppression, it can indeed modulate HCPro function by its self-cleavage activity. To study P1 protease regulation, we used bioinformatic analysis and in vitro activity experiments to map the core C-terminal catalytic domain. We present evidence that the hypervariable region that precedes the protease domain is predicted as intrinsically disordered, and that it behaves as a negative regulator of P1 proteolytic activity in in vitro cleavage assays. In viral infections, removal of the P1 protease antagonistic regulator is associated with greater symptom severity, induction of salicylate-dependent pathogenesis-related proteins, and reduced viral loads. We suggest that fine modulation of a viral protease activity has evolved to keep viral amplification below host-detrimental levels, and thus to maintain higher long-term replicative capacity.
authors.affiliation: Departamento de Genética Molecular de Plantas, Centro Nacional de Biotecnología (CNB-CSIC), Madrid, Spain.
authors.forename: Fabio
authors.initials: F
authors.lastname: Pasin
authors.affiliation: Departamento de Genética Molecular de Plantas, Centro Nacional de Biotecnología (CNB-CSIC), Madrid, Spain.
authors.forename: Carmen
authors.initials: C
authors.lastname: Simón-Mateo
authors.affiliation: Departamento de Genética Molecular de Plantas, Centro Nacional de Biotecnología (CNB-CSIC), Madrid, Spain.
authors.forename: Juan Antonio
authors.initials: JA
authors.lastname: García
mesh_terms: D000595:Amino Acid Sequence; D015153:Blotting, Western; D002853:Chromatography, Liquid; D006790:Host-Parasite Interactions / Q000502:physiology*; D008969:Molecular Sequence Data; D010447:Peptide Hydrolases / Q000737:chemistry / Q000378:metabolism*; D010935:Plant Diseases / Q000821:virology; D017800:Potyvirus / Q000472:pathogenicity / Q000502:physiology*; D017434:Protein Structure, Tertiary / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D053719:Tandem Mass Spectrometry; D014026:Nicotiana / Q000821:virology; D014764:Viral Proteins / Q000737:chemistry / Q000378:metabolism*; D014779:Virus Replication / Q000502:physiology*
chemical_list: D014764:Viral Proteins; D010447:Peptide Hydrolases