Determining the molecular drivers of species-specific interferon-stimulated gene product 15 interactions with nairovirus ovarian tumor domain proteases

Abstract

Tick-borne nairoviruses (order Bunyavirales) encode an ovarian tumor domain protease (OTU) that suppresses the innate immune response by reversing the post-translational modification of proteins by ubiquitin (Ub) and interferon-stimulated gene product 15 (ISG15). Ub is highly conserved across eukaryotes, whereas ISG15 is only present in vertebrates and shows substantial sequence diversity. Prior attempts to address the effect of ISG15 diversity on viral protein-ISG15 interactions have focused on only a single species’ ISG15 or a limited selection of nairovirus OTUs. To gain a more complete perspective of OTU-ISG15 interactions, we biochemically assessed the relative activities of 14 diverse nairovirus OTUs for 12 species’ ISG15 and found that ISG15 activity is predominantly restricted to particular nairovirus lineages reflecting, in general, known virus-host associations. To uncover the underlying molecular factors driving OTUs affinity for ISG15, X-ray crystal structures of Kupe virus and Ganjam virus OTUs bound to sheep ISG15 were solved and compared to complexes of Crimean-Congo hemorrhagic fever virus and Erve virus OTUs bound to human and mouse ISG15, respectively. Through mutational and structural analysis seven residues in ISG15 were identified that predominantly influence ISG15 species specificity among nairovirus OTUs. Additionally, OTU residues were identified that influence ISG15 preference, suggesting the potential for viral OTUs to adapt to different host ISG15s. These findings provide a foundation to further develop research methods to trace nairovirus-host relationships and delineate the full impact of ISG15 diversity on nairovirus infection.

HERC5 and the ISGylation Pathway: Critical Modulators of the Antiviral Immune Response

“…For example, viral ovarian tumor domains are common among the Nairovirus family, each retaining at least a small level of deubiquitylation activity. Moreover, a pathogenic clade containing the Crimean-Congo hemorrhagic fever virus (CCHFV), Nairobi sheep disease virus (NSDV), Ganjam virus (GANV) and Erve virus (ERVEV) also possess significant deISGylation activity [126][127][128]. Experimental evidence suggests that viral ovarian tumor family-like domains (vOTUs) have adapted to deISGylate in their most common host species and that deISGylation is likely a major hurdle that viruses must cross to change host specificity [127,129].…”

“…Moreover, a pathogenic clade containing the Crimean-Congo hemorrhagic fever virus (CCHFV), Nairobi sheep disease virus (NSDV), Ganjam virus (GANV) and Erve virus (ERVEV) also possess significant deISGylation activity [126][127][128]. Experimental evidence suggests that viral ovarian tumor family-like domains (vOTUs) have adapted to deISGylate in their most common host species and that deISGylation is likely a major hurdle that viruses must cross to change host specificity [127,129]. Interestingly, the most fatal virus in humans, CCHFV, is capable of both deubiquitylating and deISGylating target proteins, likely resulting in subversion of both the antiviral and inflammatory responses [126,130].…”

The Structure and Immune Regulatory Implications of the Ubiquitin-Like Tandem Domain Within an Avian 2’-5’ Oligoadenylate Synthetase-Like Protein

“…None fully processed the substrate in less than 2 hours. Viral OTUs demonstrate clear species preferences when processing ISG15s and the rate of cleavage demonstrated by these OTUs is similar to what is seen when known deISGylases are incubated with ISG15s from non-host species (24,38). Specificity of OTU deOASLylase activity was additionally assessed using two distantly related avian OASLs from penguin and eagle (Supplemental Figure 1).…”

“…The importance of ISG15 and Ub for successful antiviral responses are highlighted by the evolution of viruses encoding proteases that target these proteins such as the ovarian tumor domain proteases (OTU)s of Nairoviruses and papain-like proteases (PLpro) of coronaviruses (14,(21)(22)(23). These viral proteases reverse post-translational modifications by Ub and ISG15 by cleaving the conjugation created at their C-terminal LRLRGG motifs and generally preferentially cleave immunologically relevant poly-Ub chains and ISG15s from their virus' host species (24,25). Based on this activity it is possible that some viral OTUs and PLpro's have adapted to target similar immunologically relevant Ubls such as OASL (26,27).…”

Host Cell Restriction Factors of Bunyaviruses and Viral Countermeasures

“…Indeed, ISG15 is a protein that is found only in vertebrates and that is highly divergent between species. The preferences toward the ISG15 from one or another species generally reflects the preferential hosts infected by the virus [ 171 ], hinting that a co-evolution process may have contributed to these specificities.…”