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Mutation of chicken anemia virus VP2 differentially affects serine/threonine and tyrosine protein phosphatase activities

Michelle A. Peters^1,

¹ Department of Veterinary Science, The University of Melbourne, Victoria 3010, Australia
² Department of Microbiology and Immunology, The University of Melbourne, Victoria 3010, Australia
³ Division of Infection and Immunity, The Walter and Eliza Hall Institute of Medical Research, The Royal Melbourne Hospital, Victoria 3050, Australia

Correspondence
Glenn F. Browning
glenfb{at}unimelb.edu.au

Novel dual-specificity protein phosphatases (DSPs), which catalyse the removal of phosphate from both phosphotyrosine and phosphoserine/phosphothreonine substrates, have recently been identified in two viruses within the family Circoviridae. Viral protein 2 (VP2) of chicken anemia virus (CAV) and ORF2 of TT virus have been shown to possess DSP activity in vitro. CAV VP2 is unusual in possessing two vicinal cysteines within the protein phosphatase signature motif. The first cysteine residue (C95) within the motif has been identified by mutagenesis as the essential catalytic cysteine. In this study, it was shown that virus mutated at this residue displayed a marked inhibition of growth, with titres reduced 10⁴-fold, and reduced cytopathogenic effect in cell culture, indicating that viral DSP activity may be significant during infection. As with virus mutated at the first cysteine residue, mutation of the second cysteine (C97) within the motif resulted in a marked reduction in viral growth and attenuation of cytopathogenicity in infected cell cultures. However, mutagenesis of this second cysteine only reduced phosphotyrosine phosphatase activity to 70 % of that of wild-type VP2, but increased phosphoserine/phosphothreonine phosphatase activity by as much as 700 %. The differential effect of the C97S mutation on VP2 activity does not appear to have parallels in other DSPs and suggests a unique role for the second cysteine in the function of these viral proteins, particularly in vivo.

Present address: Department of Veterinary Pathobiology, Purdue University, 406 Sth University Dve, ADDL-47907, West Lafayette, IN, USA.

This article has been cited by other articles:

				M. A. Peters, B. S. Crabb, K. A. Tivendale, and G. F. Browning Attenuation of chicken anemia virus by site-directed mutagenesis of VP2 J. Gen. Virol., August 1, 2007; 88(8): 2168 - 2175. [Abstract] [Full Text] [PDF]

				M. A. Peters, B. S. Crabb, E. A. Washington, and G. F. Browning Site-directed mutagenesis of the VP2 gene of Chicken anemia virus affects virus replication, cytopathology and host-cell MHC class I expression. J. Gen. Virol., April 1, 2006; 87(Pt 4): 823 - 831. [Abstract] [Full Text] [PDF]