Structural And Functional Investigation Of Cirmean-Congo Hemorrhagic Fever Virus Nucleoprotein

Crimean-Congo hemorrhagic fever (CCHF) is a severe human disease whichoccurs in over30countries in Asia, the Middle East, Southeastern Europe, and Africaand results in high mortality. CCHF is one of the most severe insect-borne diseases inChina, mostly prevailing in Northwest China (also called as XinJiang HF, XHF). Thecausative agent of CCHF is believed to be Crimean-Congo hemorrhagic fever virus(CCHFV), which belongs to the genus Nairovirus within the family Bunyaviridae.Tick is the transmission vector of CCHFV. Bit by ticks carrying CCHFV may causesevere fever, hemorrhagic, kidney failure, cardiac and pulmonary insufficiency, themortality is as high as30percent. CCHFV is classified as a Biosafety Level4pathogen due to its rapid transmission ability, high mortality, and the possibility to beused as potential bioterrorism agent. Little is known of the packaging model of viralgenomic RNA and the mRNA transcription machinery.Nucleocapsid protein (NP) scaffolds the viral genome into ribonucleoprotein(RNP) complexes, protecting viral RNA from host cell degradation. NP also plays acritical role in viral RNA transcription and replication by interacting with L protein.The correct binding of NP with viral genomic RNA is pivotal for CCHFV assemblyand maturation. Structure insight into CCHFV NP will provide direct and preciseproof for the elucidation of virus genome packaging and mRNA transcription model.Here we report a2.3-resolution crystal structure of CCHFV nucleoprotein.CCHFV NP is composed mostly by á-helix, displays a racket-shaped overall structurewith distinct “head” and “stalk” domains, which differ significantly with NPs reportedso far from other negative-sense single-stranded RNA viruses. The electrostaticpotential surface of CCHFV NP displays several positive regions, whereas CCHFVNP unexpectedly shows very weak binding activity with RNA in vitro.Besides structural investigation, we also carried out series of biochemicalexperiment to explore the function of CCHFV NP, such as oligomeric state, bindingaffinity with RNA and mRNA cap analog, interaction with host defense related protein.CCHFV NP shows distinct feature compare with some other negative single strandedRNA virus nucleoprotein.Our work provides a new insight into the biological role of NPs in bunyavirus genome package mechanism, and gives the direct implication of transcription andreplication machinery. Moreover, our work provides a new target and valuableinformation for the development of intervention strategies to lessen the pathogenicburden of this important group of viral infections.