Briggs Group
Enveloped viruses and coated vesicles – cryo-electron microscopy and tomography
3D reconstruction of HIV-1 virions using cryo-electron microscopy (Briggs et al. 2006)
Correlated fluorescence and electron microscopy can be used to locate an individual fluorescent virus particle at the surface of a cell (Kukulski et al. 2011)
A high-resolution cryo-EM structure of an immature retrovirus capsid protein dimer (grey), fitted with available X-ray structures (Bharat et al. 2012)
A comparison of the arrangement of a retrovirus capsid protein in the immature (top) and mature (bottom) virus particles, showing dramatic conformational change (Bharat et al. 2012)
The Briggs group uses cryo-electron microscopy techniques to explore the mechanisms of assembly and budding of enveloped viruses and coated vesicles.
Previous and current research
We aim to understand how enveloped virus particles (such as HIV and Influenza virus) and coated transport vesicles (such as clathrin or COPI coated vesicles) are assembled. To make a virus or a vesicle, the building blocks and the cargo of the virus or vesicle are gathered together and interact with a lipid membrane, manipulating its shape and curvature to cause budding. To explore how this is achieved we study a range of different cellular and viral specimens. Our core methods are cryo-electron microscopy, cryo-electron tomography, and correlated light and electron microscopy.
Cryo-electron microscopy techniques are particularly appropriate for studying vesicles and viruses because they allow the shape of the membrane to be observed in its native state, while preserving information about the structure and arrangement of associated proteins. Computational image processing and 3D reconstructions are used to extract and interpret this information. As well as applying existing methods, we develop and apply novel microscopy and image processing approaches.
We take a step-by-step approach to derive structural information. Correlated fluorescence and electron microscopy methods can be used to locate and characterise features of interest. 3D reconstructions of these features can be obtained using electron tomography of the biological system in its native state. These reconstructions can be better interpreted by comparison with data collected from in vitro reconstituted systems. A detailed view is obtained by fitting these reconstructions with higher resolution structures obtained using single particle or helical reconstruction methods, or by X-ray crystallography.
A particular emphasis of our research is on the structure and life-cycle of asymmetric membrane viruses, such as HIV. The structure and assembly of HIV particles offers insights into general features of membrane budding. Further details on our research into the structure and inhibition of HIV are available on our Molecular Medicine Partnership Unit webpage.
Future projects and goals
Our goal is to understand the interplay between protein assemblies, membrane shape and virus/vesicle structure. How do proteins induce the distortion of cellular membranes into vesicles of different dimensions? What are the similarities and differences between the variety of cellular budding events? How do viruses hijack cellular systems for their own use? What is the role and arrangement of the cytoskeleton during membrane distortions? How does the curvature of a membrane influence its interaction with particular proteins? What kind of protein-protein interactions can drive virus assembly while maintaining structural flexibility? We are developing and applying novel microscopy and image processing approaches to address these questions.
3D reconstructions of COPI coated vesicles obtained using cryo-electron tomography and sub-tomogram averaging (Faini et al. 2012)
