Arterivirus PLP2 : an OTU deubiquitinase that counteracts Innate Immunity

Abstract

The work described in this thesis provides novel insights into the structural and (multi)functional characteristics of arterivirus PLP2. This enzyme plays an essential role in the viral replication cycle by cleaving the viral replicase polyproteins. In addition, there were indications that PLP2 is able to influence certain cellular processes by cleaving ubiquitin. We have now shown that PLP2 indeed functions as a deubiquitinating enzyme (DUB) and that this activity is important for the suppression of the innate immune response in the cell. To be able to separate both functions of PLP2 we have solved the crystal structure of this enzyme in complex with ubiquitin. Based on this structure, we were able to design mutations in PLP2 that selectively disrupt the interaction with ubiquitin, without interfering with cleavage of the viral polyproteins. Using these mutants, we have demonstrated for the first time the importance of a viral DUB in the evasion of innate immunity in the context of an infection. The acquired knowledge can now be applied to the design of improved arterivirus vaccines and studies of other viral DUBs, including those encoded by the zoonotic coronaviruses that cause SARS and MERS.