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"Natively Unfolded" VPg Is Essential for Sesbania Mosaic Virus Serine Protease Activity

Satheshkumar, Panayampalli Subbian and Gayathri, Pananghat and Prasad, Kasaragod and Savithri, Handanahal Subbarao (2005) "Natively Unfolded" VPg Is Essential for Sesbania Mosaic Virus Serine Protease Activity. In: Journal of Biological Chemistry, 280 (34). pp. 30291-30300.

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Polyprotein processing is a major strategy used by many plant and animal viruses to maximize the number of protein products obtainable from a single open reading frame. In Sesbania mosaic virus, open reading frame-2 codes for a polyprotein that is cleaved into different functional proteins in cis by the N-terminal serine protease domain. The soluble protease domain lacking 70-amino-acid residues from the N terminus ($\triangle$N70Pro, where Pro is protease) was not active in trans. Interestingly, the protease domain exhibited trans-catalytic activity when VPg (viral protein genome-linked) was present at the C terminus. Bioinformatic analysis of VPg primary structure suggested that it could be a disordered protein. Biophysical studies validated this observation, and VPg resembled "natively unfolded" proteins. CD spectral analysis showed that the $\triangle$N70Pro-VPg fusion protein had a characteristic secondary structure with a 230 nm positive CD peak. Mutation of Trp-43 in the VPg domain to phenylalanine abrogated the positive peak with concomitant loss in cis- and trans-proteolytic activity of the $\triangle$N70Pro domain. Further, deletion of VPg domain from the polyprotein completely abolished proteolytic processing. The results suggested a novel mechanism of activation of the protease, wherein the interaction between the natively unfolded VPg and the protease domains via aromatic amino acid residues alters the conformation of the individual domains and the active site of the protease. Thus, VPg is an activator of protease in Sesbania mosaic virus, and probably by this mechanism, the polyprotein processing could be regulated in planta.

Item Type: Journal Article
Publication: Journal of Biological Chemistry
Publisher: The American Society for Biochemistry and Molecular Biology
Additional Information: The Copyright belongs to The American Society for Biochemistry and Molecular Biology
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Division of Biological Sciences > Biochemistry
Date Deposited: 06 Mar 2006
Last Modified: 19 Sep 2010 04:23
URI: http://eprints.iisc.ac.in/id/eprint/5483

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