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Journal of Virology, October 2005, p. 12382-12393, Vol. 79, No. 19
0022-538X/05/$08.00+0     doi:10.1128/JVI.79.19.12382-12393.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Identification of Complement Regulatory Domains in Vaccinia Virus Complement Control Protein

Jayati Mullick,{dagger} John Bernet,{dagger} Yogesh Panse, Sharanabasava Hallihosur, Akhilesh K. Singh, and Arvind Sahu*

National Centre for Cell Science, Pune University Campus, Ganeshkhind, Pune 411007, India

Received 22 March 2005/ Accepted 7 July 2005

Vaccinia virus encodes a homolog of the human complement regulators named vaccinia virus complement control protein (VCP). It is composed of four contiguous complement control protein (CCP) domains. Previously, VCP has been shown to bind to C3b and C4b and to inactivate the classical and alternative pathway C3 convertases by accelerating the decay of the classical pathway C3 convertase and (to a limited extent) the alternative pathway C3 convertase, as well as by supporting the factor I-mediated inactivation of C3b and C4b (the subunits of C3 convertases). In this study, we have mapped the CCP domains of VCP important for its cofactor activities, decay-accelerating activities, and binding to the target proteins by utilizing a series of deletion mutants. Our data indicate the following. (i) CCPs 1 to 3 are essential for cofactor activity for C3b and C4b; however, CCP 4 also contributes to the optimal activity. (ii) CCPs 1 to 2 are enough to mediate the classical pathway decay-accelerating activity but show very minimal activity, and all the four CCPs are necessary for its efficient activity. (iii) CCPs 2 to 4 mediate the alternative pathway decay-accelerating activity. (iv) CCPs 1 to 3 are required for binding to C3b and C4b, but the presence of CCP 4 enhances the affinity for both the target proteins. These results together demonstrate that the entire length of the protein is required for VCP's various functional activities and suggests why the four-domain structure of viral CCP is conserved in poxviruses.


* Corresponding author. Mailing address: National Centre for Cell Science, Pune University Campus, Ganeshkhind, Pune 411007, India. Phone: 91-20-2569-0922. Fax: 91-20-2569-2259. E-mail: arvindsahu{at}nccs.res.in.

{dagger} J.M. and J.B. contributed equally to this work.


Journal of Virology, October 2005, p. 12382-12393, Vol. 79, No. 19
0022-538X/05/$08.00+0     doi:10.1128/JVI.79.19.12382-12393.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.




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Copyright © 2005 by the American Society for Microbiology. All rights reserved.