Phosphorylation of the Potyvirus Capsid Protein by Protein Kinase CK2 and Its Relevance for Virus Infection

• Published in: The Plant cell Vol. 15; no. 9; pp. 2124 - 2139
• Main Authors: Ivanov, Konstantin I., Puustinen, Pietri, Gabrenaite, Rasa, Vihinen, Helena, Rönnstrand, Lars, Valmu, Leena, Kalkkinen, Nisse, Mäkinen, Kristiina
• Format: Journal Article
• Language: English
• Published: England American Society of Plant Biologists 01.09.2003
• Subjects: Amino Acid Sequence; Amino acids; Antibodies; Capsid proteins; Capsid Proteins - genetics; Capsid Proteins - isolation & purification; Capsid Proteins - metabolism; Capsid Proteins/genetics/isolation & purification/metabolism; Casein Kinase II; Catalysis; Consensus sequence; Dichlororibofuranosylbenzimidazole - pharmacology; Gels; Gene expression regulation; Gene Expression Regulation, Enzymologic - drug effects; Gene Expression Regulation, Plant - drug effects; Liquid chromatography; Mass spectrometry; Molecular Sequence Data; Mutation; Nicotiana - enzymology; Nicotiana - virology; Phosphorylation; Phosphorylation - drug effects; Plant cells; Plant Proteins - genetics; Plant Proteins - metabolism; Plant Proteins/genetics/metabolism; Potyvirus - growth & development; Potyvirus - metabolism; Potyvirus/growth & development/metabolism; Protein Serine-Threonine Kinases - antagonists & inhibitors; Protein Serine-Threonine Kinases - genetics; Protein Serine-Threonine Kinases - metabolism; Protein-Serine-Threonine Kinases/antagonists & inhibitors/genetics/metabolism; Proteins; Protoplasts - metabolism; Protoplasts - virology; Protoplasts/metabolism/virology; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Recombinant Proteins/genetics/metabolism; RNA; RNA-Binding Proteins - genetics; RNA-Binding Proteins - metabolism; RNA-Binding Proteins/genetics/metabolism; Threonine - metabolism; Tobacco; Tobacco/enzymology/virology; Viruses; Plant/drug effects; Enzymologic/drug effects; Gene Expression Regulation
• ISSN: 1040-4651; 1532-298X; 1532-298X
• DOI: 10.1105/tpc.012567

We reported previously that the capsid protein (CP) of Potato virus A (PVA) is phosphorylated both in virus-infected plants and in vitro. In this study, an enzyme that phosphorylates PVA CP was identified as the protein kinase CK2. The α-catalytic subunit of CK2 (CK2α) was purified from tobacco and characterized using in-gel kinase assays and liquid chromatography-tandem mass spectrometry. The tobacco CK2α gene was cloned and expressed in bacterial cells. Specific antibodies were raised against the recombinant enzyme and used to demonstrate the colocalization of PVA CP and CK2α in infected tobacco protoplasts. A major site of CK2 phosphorylation in PVA CP was identified by a combination of mass spectrometric analysis, radioactive phosphopeptide sequencing, and mutagenesis as Thr-242 within a CK2 consensus sequence. Amino acid substitutions that affect the CK2 consensus sequence in CP were introduced into a full-length infectious cDNA clone of PVA tagged with green fluorescent protein. Analysis of the mutant viruses showed that they were defective in cell-to-cell and long-distance movement. Using in vitro assays, we demonstrated that CK2 phosphorylation inhibited the binding of PVA CP to RNA, suggesting a molecular mechanism of CK2 action. These results suggest that the phosphorylation of PVA CP by CK2 plays an important regulatory role in virus infection.