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Equine arteritis virus papain-like protease 2 (PLP2) covalently bound to ubiquitin
Structural highlights
FunctionRPOA_EAVBU The replicase polyprotein 1ab is a multifunctional protein: it contains the activities necessary for the transcription of negative stranded RNA, leader RNA, subgenomic mRNAs and progeny virion RNA as well as proteinases responsible for the cleavage of the polyprotein into functional products.[1] Nsp1 is essential for viral subgenomic mRNA synthesis.[2] Nsp2 cysteine proteinase which cleaves the nsp2/nsp3 site in the polyprotein. Also displays deubiquitinating and deISGylase activities. The deubiquitinating activity cleaves both ubiquitinated and ISGylated products and may therefore regulate ubiquitin and ISG15 dependent host innate immunity.[3] The 3C-like serine proteinase chain is responsible for the majority of cleavages as it cleaves the C-terminus of the polyprotein.[4] The helicase chain, which contains a zinc finger structure, displays RNA and DNA duplex-unwinding activities with 5' to 3' polarity.[5] Publication Abstract from PubMedProtein ubiquitination regulates important innate immune responses. The discovery of viruses encoding deubiquitinating enzymes (DUBs) suggests they remove ubiquitin to evade ubiquitin-dependent antiviral responses; however, this has never been conclusively demonstrated in virus-infected cells. Arteriviruses are economically important positive-stranded RNA viruses that encode an ovarian tumor (OTU) domain DUB known as papain-like protease 2 (PLP2). This enzyme is essential for arterivirus replication by cleaving a site within the viral replicase polyproteins and also removes ubiquitin from cellular proteins. To dissect this dual specificity, which relies on a single catalytic site, we determined the crystal structure of equine arteritis virus PLP2 in complex with ubiquitin (1.45 A). PLP2 binds ubiquitin using a zinc finger that is uniquely integrated into an exceptionally compact OTU-domain fold that represents a new subclass of zinc-dependent OTU DUBs. Notably, the ubiquitin-binding surface is distant from the catalytic site, which allowed us to mutate this surface to significantly reduce DUB activity without affecting polyprotein cleavage. Viruses harboring such mutations exhibited WT replication kinetics, confirming that PLP2-mediated polyprotein cleavage was intact, but the loss of DUB activity strikingly enhanced innate immune signaling. Compared with WT virus infection, IFN-beta mRNA levels in equine cells infected with PLP2 mutants were increased by nearly an order of magnitude. Our findings not only establish PLP2 DUB activity as a critical factor in arteriviral innate immune evasion, but the selective inactivation of DUB activity also opens unique possibilities for developing improved live attenuated vaccines against arteriviruses and other viruses encoding similar dual-specificity proteases. Deubiquitinase function of arterivirus papain-like protease 2 suppresses the innate immune response in infected host cells.,van Kasteren PB, Bailey-Elkin BA, James TW, Ninaber DK, Beugeling C, Khajehpour M, Snijder EJ, Mark BL, Kikkert M Proc Natl Acad Sci U S A. 2013 Feb 11. PMID:23401522[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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