ZUP1 and viral infectious disease: PLpro is a deubiquitinase (DUB) removingubiquitin (Ub) and ubiquitin-like proteins (UbL), most importantlyinterferon-stimulated gene product 15 (ISG15), from host proteins.15−21 ISG modification of host proteins is a key component of the innateimmune response to viral infection and PLpro has evolved to have thegreatest DUB efficiency toward ISGylated host proteins.18,22