Structure of interferon-stimulated gene product 15 (ISG15) from the bat species Myotis davidii and the impact of interdomain ISG15 interactions on viral protein engagement

Abstract

Bats have long been observed to be the hosts and the origin of numerous human diseases. Bats, like all mammals, rely on a number of innate immune mechanisms to combat invading pathogens, including the interferon type I, II and III responses. Ubiquitin-like interferon-stimulated gene product 15 (ISG15) is a key modulator of these interferon responses. Within these pathways, ISG15 can serve to stabilize host proteins modulating innate immune responses and act as a cytokine. Post-translational modifications of viral proteins introduced by ISG15 have also been observed to directly affect the function of numerous viral proteins. Unlike ubiquitin, which is virtually identical across all animals, comparison of ISG15s across species reveals that they are relatively divergent, with sequence identity dropping to as low as $58% among mammals. In addition to serving as an obstacle to the zoonotic transmission of influenza, these ISG15 species-species differences have also long been shown to have an impact on the function of viral deISGylases. Recently, the structure of the first nonhuman ISG15, originating from mouse, suggested that the structures of human ISG15 may not be reflective of other species. Here, the structure of ISG15 from the bat species Myotis davidii solved to 1.37 Å resolution is reported. Comparison of this ISG15 structure with those from human and mouse not only underscores the structural impact of ISG15 species-species differences, but also highlights a conserved hydrophobic motif formed between the two domains of ISG15. Using the papain-like deISGylase from Severe acute respiratory syndrome coronavirus as a probe, the biochemical importance of this motif in ISG15-protein engagements was illuminated.

ISG15: It's Complicated

“…Mouse ISG15, on the other hand, possesses a wider hydrophobic interface that is less constricting of the interdomain arrangement. This theme was further bolstered with the recently reported structure of vesper bat ISG15 that showed an even wider range of structural modes than previously observed [66]. It also revealed the central role of a highly conserved phenylalanine (Phe40/41) in the N-terminal domain in forming the interdomain contact regardless of the overall structure.…”

“…Beyond the effect of species variance within potential proteineprotein interfaces, evidence has [53,61e63] and PDB entries 3R66 and 6BI8), murine ISG15 (gold, [59,64,65] and PDB entries 5CHF and 5CHW), bat ISG15 (blue, [66]), bovine ISG15 (cyan green, [65]), and canine ISG15 (dark teal, [65]) were overlaid to identify the trends in domainedomain orientations between species. Representative chains were selected for each species.…”

Conformational Dynamics in the Interaction of SARS-CoV-2 Papain-like Protease with Human Interferon-Stimulated Gene 15 Protein

“…Residue variations in this region that are found in different species of ISG15s can lead to biochemical differences in ISG15–protein engagement. 6 , 20 Comparison of human, mouse, and bat ISG15s showed differences in how a conserved Phe40 is buried within the interface in the hydrophobic patch 20 that may explain the differences between PLpro:mISG15 and PLpro:hISG15 complexes observed here. In addition, a conserved Pro39 present in most ISG15s is replaced by a histidine in the hISG15, which could result in steric and electrostatic factors that limit the conformations that ISG15 can adopt in different species.…”

“…However, the peak at ∼35 Å in the P ( r ) profile is more prominent and shifted to longer distances compared to the theoretical profile, indicating that the two domains of hISG15 in solution are more separated than in the crystal structure. Langley et al 20 compared human, mouse, and bat ISG15 structures (PDB entries 1Z2M, 5TLA, and 6MDH, respectively) and showed a difference in the twist around the N- and C-terminal domains that could be attributed to differences in the flexible hinge region connecting the two domains. Calculation of the theoretical P ( r ) profiles of these proteins also presents the expected bimodal distribution.…”

More than Meets the ISG15: Emerging Roles in the DNA Damage Response and Beyond

“…ISG15 orthologues can be found in various organisms although cross-species conservation of amino-acid sequences is relatively low even amongst mammals ( Figure 1 D) [ 24 , 25 ]. Moreover, the orientation of the two ISG15 UBL domains varies considerably across species [ 26 , 27 , 28 ], contrasting with the almost 100% cross-species conservation of ubiquitin [ 29 ], suggesting that ISG15 is an evolutionarily diverse and non-essential gene.…”