title: Biochemical characterization of C4 protein of Cotton leaf curl Kokhran Virus-Dabawali.
abstract: BACKGROUND
  Cotton leaf curl Kokhran Virus-Dabawali (CLCuKV-Dab) is a monopartite begomovirus encoding two proteins V1 and V2 in the virion sense and four proteins C1, C2, C3 and C4 in the complementary sense. The C4 protein of monopartite begomoviruses has been implicated to play a role in symptom determination and virus movement. The present work aims at the biochemical characterization of this protein.
  
  
  METHODS
  The C4 protein of CLCuKV-Dab was purified in fusion with GST and tested for the ability to hydrolyze ATP and other phosphate containing compounds. ATPase activity was assayed by using radiolabeled γ-[32P]-ATP and separating the product of reaction by thin layer chromatography. The hydrolysis of other compounds was monitored by the formation of a blue colored phosphomolybdate complex which was estimated by measuring the absorbance at 655nm.
  
  
  RESULTS
  The purified GST-C4 protein exhibited metal ion dependent ATPase and inorganic pyrophosphatase activities. Deletion of a sequence resembling the catalytic motif present in phosphotyrosine phosphatases resulted in 70% reduction in both the activities. Mutational analysis suggested arginine 13 to be catalytically important for the ATPase and cysteine 8 for the pyrophosphatase activity of GST-C4. Interaction of V2 with GST-C4 resulted in an increase in both the enzymatic activities of GST-C4.
  
  
  CONCLUSIONS
  The residues important for the enzymatic activities of GST-C4 are present in a motif different from the classical Walker motifs and the non-classical ATP binding motifs reported so far.
  
  
  CONCLUSIONS
  The C4 protein of CLCuKV-Dab, a putative natively unfolded protein, exhibits enzymatic activities.
authors.affiliation: Department of Biochemistry, Indian Institute of Science, Bangalore, India.
authors.forename: Debojit
authors.initials: D
authors.lastname: Guha
authors.forename: C G
authors.initials: CG
authors.lastname: Poornima Priyadarshini
authors.forename: Arunima
authors.initials: A
authors.lastname: Purakayastha
authors.forename: R
authors.initials: R
authors.lastname: Thippeswamy
authors.forename: M
authors.initials: M
authors.lastname: Lakshmikanth
authors.forename: H S
authors.initials: HS
authors.lastname: Savithri
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020816:Amino Acid Motifs; D053839:Begomovirus / Q000201:enzymology* / Q000235:genetics; D020134:Catalytic Domain; D043564:Inorganic Pyrophosphatase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017510:Protein Folding; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D014764:Viral Proteins; D000251:Adenosine Triphosphatases; D043564:Inorganic Pyrophosphatase