Structural cell biology of Rift Valley fever and Hazara bunyaviruses

• Applicant: Dr. Jan Hellert
• Subject Area: Virology ; Structural Biology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 518614462

The WHO R&D Blueprint lists Rift Valley fever phlebovirus (RVFV, BSL3) and Crimean-Congo hemorrhagic fever orthonairovirus (CCHFV, BSL4) as high-priority targets for research and development. The two pathogens are arthropod-borne zoonotic bunyaviruses that can cause lethal infection in humans. The geographic ranges of their arthropod vectors are currently expanding in the course of climate change. An important step in the life cycle of all bunyaviruses is the budding of new virions from parental host cells, which involves the formation of a viral envelope to enclose the viral genetic material in the form of three ribonucleoprotein complexes. This envelope is composed of a lipid bilayer decorated with two or three different viral glycoproteins in a locally ordered pattern. Although the structures of several bunyavirus envelopes have already been well characterized in their mature state, the process of their morphogenesis during budding is still poorly understood. The reason for this lack of knowledge is that budding occurs intracellularly, where the study of molecular structural details is particularly challenging. Another important step in the life cycle of bunyaviruses is the antagonism of the cellular innate immune response. For this purpose, RVFV produces long filaments of its major virulence factor NSs inside the host cell nuclei that sequester and degrade cellular components of the innate immune response. Here, I propose pioneering structural studies of bunyavirus morphogenesis at intracellular membranes and of NSs nuclear filament architecture using high-resolution native electron cryo-tomography (cryo-ET) of focused-ion-beam-thinned frozen-hydrated infected cells. The attenuated RVFV isolate MP-12 and the commonly used non-zoonotic CCHFV surrogate Hazara orthonairovirus (HAZV) will serve as model systems to be used in the state-of-the-art BSL2 cryo-EM facility of the Centre for Structural Systems Biology (CSSB) in Hamburg. For structure determination of the native NSs filaments, the in-situ cryo-ET analysis will be complemented with a single-particle cryo-EM analysis of purified NSs filaments in the absence or presence of purified cellular binding partners that will be added to the filaments in vitro. This project will provide unprecedented mechanistic insight into the assembly of bunyavirus envelopes as well as into RVFV NSs filament architecture and host factor binding inside infected cells, which will provide valuable knowledge for the development of future vaccines and antiviral drugs.

• DFG Programme: Research Grants
• International Connection: United Kingdom
• Cooperation Partner: Daven Vasishtan, Ph.D.