A Deubiquitinating Enzyme Encoded by HSV-1 Belongs to a Family of Cysteine Proteases that Is Conserved across the Family Herpesviridae

Abstract

We have discovered a ubiquitin (Ub)-specific cysteine protease encoded within the N-terminal approximately 500 residues of the UL36 gene product, the largest (3164 aa) tegument protein of herpes simplex virus 1 (HSV-1). Enzymatic activity of this fragment, UL36USP, is detectable only after cleavage of UL36USP from full-length UL36 and occurs late during viral replication. UL36USP bears no homology to known deubiquitinating enzymes (DUBs) or Ub binding proteins. Sequence alignment of the large tegument proteins across the family Herpesviridae indicates conservation of key catalytic residues amongst these viruses. Recombinant UL36USP exhibits hydrolytic activity toward Ub-AMC and ubiquitinated branched peptides in vitro. In addition, recombinant UL36USP can cleave polyUb chains and appears to be specific for Lys48 linkages. Mutation of the active site cysteine residue (Cys65) to alanine abolishes this enzymatic activity. The lack of homology between UL36USP and eukaryotic DUBs makes this new family of herpesvirus ubiquitin-specific proteases attractive targets for selective inhibition.

A herpesvirus ubiquitin-specific protease is critical for efficient T cell lymphoma formation

“…In HSV-1, the U L 36-derived USP was discovered as an Ϸ450-aa amino-terminal fragment of the VP1/2 tegument protein, generated late during viral infection (12). So far, only HSV-1 has yielded an enzymatically active, proteolytic fragment that is distinct from the intact tegument protein in virus-infected cells.…”

“…Nonetheless, sequence comparisons across the Herpesviridae show the presence of a few absolutely conserved residues (Cys, Asp, His, Glu), all of which are consistent with involvement in a potential thiol protease active site. We have, meanwhile, confirmed both the mechanism of action of such ubiquitin-based probes (11)(12)(13)(14)(15) and the identity of the viral cysteine protease domain as an authentic USP by crystallographic analysis of the homologous segment of the murine cytomegalovirus (MCMV) M48 protein (16). Notwithstanding the conservation of the identified USP activity in all herpesviruses, we do not know whether this activity makes a contribution to the replicative success and pathogenicity of herpesviruses in vivo.…”

Severe acute respiratory syndrome coronavirus papain-like protease: Structure of a viral deubiquitinating enzyme

“…For example, the NS1B protein of influenza B virus prevents ISGylation of proteins by binding to ISG15 (37). Like SARS-CoV PLpro, a number of viral proteases have also been shown to deconjugate Ubl modifiers, including proteases from herpes simplex virus 1 and homologues (38,39), African swine fever virus (40), and adenovirus (41). By analogy, these parallel studies strongly suggest the possibility that SARS-CoV uses similar mechanisms of protection against ubiquitination or ISGylation.…”

Evolution of a signalling system that incorporates both redundancy and diversity:ArabidopsisSUMOylation

“…The AtULP1s used in our studies had been classified based on sequence identity with known ULP1s. Recently, a deubiquitinating enzyme (DUB) from herpes simplex virus 1 was discovered, and interestingly, this enzyme showed no sequence homology with any known de-ubiquitinating enzyme [28]. Based on this finding, it is possible that other proteins in Arabidopsis have ULP1 activity, but do not share sequence homology with known ULP1s.…”