Virulence Factor of Potato Virus Y, Genome-attached Terminal Protein VPg, Is a Highly Disordered Protein

Abstract

Potato virus Y (PVY) is a common potyvirus of agricultural importance, belonging to the picornavirus superfamily of RNA plus-stranded viruses. A covalently linked virus-encoded protein VPg required for virus infectivity is situated at the 5 end of potyvirus RNA. VPg seems to be involved in multiple interactions, both with other viral products and host proteins. VPgs of potyviruses have no known homologs, and there is no atomic structure available. To understand the molecular basis of VPg multifunctionality, we have analyzed structural features of VPg from PVY using structure prediction programs, functional assays, and biochemical and biophysical analyses. Structure predictions suggest that VPg exists in a natively unfolded conformation. In contrast with ordered proteins, PVY VPg is not denatured by elevated temperatures, has sedimentation values incompatible with a compact globular form, and shows a CD spectrum of a highly disordered protein, and HET-HETSOFAST NMR analysis suggests the presence of large unstructured regions. Although VPg has a propensity to form dimers, no functional differences were seen between the monomer and dimer. These data strongly suggest that the VPg of PVY should be classified among intrinsically disordered proteins. Intrinsic disorder lies at the basis of VPg multifunctionality, which is necessary for virus survival in the host.

Protein-RNA linkage and post-translational modifications of two sobemovirus VPgs

“…For Potato virus A (PVA), Potato virus Y, Lettuce mosaic virus, SeMV and RYMV an unfolded/disordered structure of VPg has been described previously (Grzela et al, 2008;Hébrard et al, 2009;Rantalainen et al, 2008;Satheshkumar et al, 2005). VPg proteins lack a unique 3D-structure and exist as a dynamic ensemble of conformations.…”

Control of Nuclear and Nucleolar Localization of Nuclear Inclusion Protein a of Picorna-LikePotato virus AinNicotianaSpecies

“…Substitution of this Tyr residue with other amino acids abolishes infectivity of both viruses (Murphy et al, 1996;Germundsson et al, 2007). The intrinsically disordered structure of VPg (Grzela et al, 2008;Rantalainen et al, 2008) provides flexibility for many types of interactions with viral and host proteins (Hong et al, 1995;Li et al, 1997;Wittmann et al, 1997;Schaad et al, 2000;Guo et al, 2001;Dunoyer et al, 2004;Lé onard et al, 2004;Thivierge et al, 2008). Interactions between eIF4E or eIF(iso)4E (Wittmann et al, 1997;Schaad et al, 2000;Robaglia and Caranta, 2006) and VPg or NIa are important for virus infectivity (Lé onard et al, 2000;Robaglia and Caranta, 2006).…”

Structural Flexibility Allows the Functional Diversity of Potyvirus Genome-Linked Protein VPg

“…However, several recent studies have shown the intrinsic structural disorder of these proteins. The resulting structural flexibility has been proposed to enable VPg to carry out the variety of functions (16,20,40,44). The N terminus, NTP-binding region, and a short segment in the middle of the protein were speculated to be part of a natively unstructured stretch of amino acids, which may allow these regions to be multifunctional and structurally flexible and thereby facilitate participation of VPg in various interactions.…”

“…It is argued by Tokuriki et al that viral proteins have a lot of flexibility and a high level of disorder and that they apparently are rapidly evolving proteins, stabilized only in the presence of partners. Accordingly, structural disorder together with polyprotein intermediates and various posttranslational modifications of VPg (18) as well as formation of VPg dimers (16,31,40) give rise to a great variety of functions and complex targets for structure-function studies.…”