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Functional Importance of Hydrophobic Patches on the Ebola Virus VP35 IFN-Inhibitory Domain.

ABSTRACT: Viral protein 35 (VP35) of Ebola virus (EBOV) is a multifunctional protein that mainly acts as a viral polymerase cofactor and an interferon antagonist. VP35 interacts with the viral nucleoprotein (NP) and double-stranded RNA for viral RNA transcription/replication and inhibition of type I interferon (IFN) production, respectively. The C-terminal portion of VP35, which is termed the IFN-inhibitory domain (IID), is important for both functions. To further identify critical regions in this domain, we analyzed the physical properties of the surface of VP35 IID, focusing on hydrophobic patches, which are expected to be functional sites that are involved in interactions with other molecules. Based on the known structural information of VP35 IID, three hydrophobic patches were identified on its surface and their biological importance was investigated using minigenome and IFN-β promoter-reporter assays. Site-directed mutagenesis revealed that some of the amino acid substitutions that were predicted to disrupt the hydrophobicity of the patches significantly decreased the efficiency of viral genome replication/transcription due to reduced interaction with NP, suggesting that the hydrophobic patches might be critical for the formation of a replication complex through the interaction with NP. It was also found that the hydrophobic patches were involved in the IFN-inhibitory function of VP35. These results highlight the importance of hydrophobic patches on the surface of EBOV VP35 IID and also indicate that patch analysis is useful for the identification of amino acid residues that directly contribute to protein functions.

SUBMITTER: Kasajima N

PROVIDER: S-EPMC8618116 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Ebolaviruses are causative agents of lethal hemorrhagic fever in humans and nonhuman primates. Among the filoviruses characterized thus far, Reston Ebola virus (REBOV) is the only Ebola virus that is nonpathogenic to humans despite the fact that REBOV can cause lethal disease in nonhuman primates. Previous studies also suggest that REBOV is less effective at inhibiting host innate immune responses than Zaire Ebola virus (ZEBOV) or Marburg virus. Virally encoded VP35 protein is critical for immune suppression, but an understanding of the relative contributions of VP35 proteins from REBOV and other filoviruses is currently lacking. In order to address this question, we characterized the REBOV VP35 interferon inhibitory domain (IID) using structural, biochemical, and virological studies. These studies reveal differences in double-stranded RNA binding and interferon inhibition between the two species. These observed differences are likely due to increased stability and loss of flexibility in REBOV VP35 IID, as demonstrated by thermal shift stability assays. Consistent with this finding, the 1.71-A crystal structure of REBOV VP35 IID reveals that it is highly similar to that of ZEBOV VP35 IID, with an overall backbone r.m.s.d. of 0.64 A, but contains an additional helical element at the linker between the two subdomains of VP35 IID. Mutations near the linker, including swapping sequences between REBOV and ZEBOV, reveal that the linker sequence has limited tolerance for variability. Together with the previously solved ligand-free and double-stranded-RNA-bound forms of ZEBOV VP35 IID structures, our current studies on REBOV VP35 IID reinforce the importance of VP35 in immune suppression. Functional differences observed between REBOV and ZEBOV VP35 proteins may contribute to observed differences in pathogenicity, but these are unlikely to be the major determinant. However, the high level of similarity in structure and the low tolerance for sequence variability, coupled with the multiple critical roles played by Ebola virus VP35 proteins, highlight the viability of VP35 as a potential target for therapeutic development.

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Functional Importance of Hydrophobic Patches on the Ebola Virus VP35 IFN-Inhibitory Domain.

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