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The order Bunyavirales is comprised of numerous emerging zoonotic pathogens which present a global threat to human health. Many bunyaviruses are arboviruses including members of the family Nairovirdae such as the tick-borne Crimean-Congo haemorrhagic fever virus that is responsible for deadly outbreaks in Africa, East Asia and Southern Europe. Also among them are members of the family Hantaviridae which include Andes and Sin Nombre virus in the American continent and Hantaan and Puumala virus in Asia and Europe respectively. These are a hosted predominantly by rodents and frequently spill over into humans populations leading to hantavirus pulmonary syndrome and haemorrhagic fever with renal syndrome. Bunyaviruses are often pleomorphic and are enveloped in a membrane harbouring just two surface glycoproteins, Gn and Gc. These glycoproteins are responsible for budding of the virus from the host cell, attachment to new target cells and release of viral RNA by membrane fusion. Furthermore, these glycoproteins are the target of the antibody-mediated host immune response and could form the basis for the development of future vaccines and immunotherapeutic medical interventions. The precise arrangement of these glycoproteins, and how these processes are mediated, are only partially understood for members of Hantaviridae and Nairoviridae. The goal of this thesis is to contribute to our understanding by addressing these topics using cryogenic electron microscopy (cryo-EM). An initial description of the nairovirus surface is presented which displays a novel lattice of glycoproteins across its surface. An improvement to our understanding of the hantavirus glycoprotein array is made which enables, in combination with available crystallographic models, a near-complete pseudo-atomic model of the hantavirus surface to be proposed. In addition, the metastable nature of this lattice is demonstrated after exposure to low pH conditions equivalent of the endocytic pathway. A hantaviral virus-like particle (VLP) system is developed to provide a safe platform for structural studies of otherwise dangerous pathogenic species. This is then used to gain insights into hantavirus receptor interactions including Andes virus and the cell surface protein protocadherin-1. The VLP system is also used to study the structural mechanism of antibody-mediated host immune responses to Puumala virus and Hantaan virus. Finally, a number of tools and optimisations to assist and improve the cryo-ET and subtomogram averaging workflows that enable these structural studies are presented. |
