A viral deubiquitylating enzyme targets viral RNA-dependent RNA polymerase and affects viral infectivity

Abstract

Selective protein degradation via the ubiquitin-proteasome system (UPS) plays an essential role in many major cellular processes, including host-pathogen interactions. We previously reported that the tightly regulated viral RNA-dependent RNA polymerase (RdRp) of the positive-strand RNA virus Turnip yellow mosaic virus (TYMV) is degraded by the UPS in infected cells, a process that affects viral infectivity. Here, we show that the TYMV 98K replication protein can counteract this degradation process thanks to its proteinase domain. In-vitro assays revealed that the recombinant proteinase domain is a functional ovarian tumour (OTU)-like deubiquitylating enzyme (DUB), as is the 98K produced during viral infection. We also demonstrate that 98K mediates in-vivo deubiquitylation of TYMV RdRp protein-its binding partner within replication complexes-leading to its stabilization. Finally, we show that this DUB activity contributes to viral infectivity in plant cells. The identification of viral RdRp as a specific substrate of the viral DUB enzyme thus reveals the intricate interplay between ubiquitylation, deubiquitylation and the interaction between viral proteins in controlling levels of RdRp and viral infectivity.

Ubiquitin and Plant Viruses, Let’s Play Together!

“…Although several DUBs have now been described in animal viruses, it is only recently that such an activity was demonstrated to be encoded by the plant virus Turnip yellow mosaic virus (TYMV; Chenon et al, 2012). TYMV DUB activity is carried by the Cys proteinase domain of the replication protein, which is also involved in endoproteolytic processing of viral proteins.…”

“…However, the most surprising finding was the recent report that such ubiquitination and degradation processes can be counteracted by another TYMV-encoded replication protein bearing a DUB activity (Chenon et al, 2012). Because proteasomal degradation of 66K could have been avoided easily by mutation of the PEST sequence during evolution, this result points to the importance of the dynamics and reversibility of ubiquitination events and underscores the idea that the virus has evolved to take advantage of both ubiquitination and deubiquitination events for implementing precise temporal and/or spatial control of its life cycle.…”

Cellular Ubc2/Rad6 E2 ubiquitin-conjugating enzyme facilitates tombusvirus replication in yeast and plants

“…Viruses also usurp UPS to target host antiviral proteins for degradation to facilitate viral infections. Viral proteins could also reverse protein ubiquitination that likely regulate viral infections (Alcaide-Loridan and Jupin, 2012; Chenon et al, 2012;Lindner, 2007;Lombardi et al, 2013).…”

Plant immunity against viruses: antiviral immune receptors in focus

“…The Turnip yellow mosaic virus (TYMV) RNA-dependent RNA polymerase (66K) is degraded by the UPS in infected cells, which compromises viral infectivity (Camborde et al, 2010). The virus, in turn, makes use of a viral deubiquitinating enzyme (DUB) to stabilize RdRp and contribute positively to infection (Chenon et al, 2012).…”