Briggs Group

Figure 1: 3D reconstruction of HIV-1 virions using cryo-electron microscopy.

Figure 2: 3D reconstruction of the SIV glycoprotein spike, generated by averaging sub-tomograms extracted from whole virus tomograms. (Zanetti et al., 2006)

Previous and current research

We are interested in how proteins can define and manipulate the shapes of membranes during budding and fusion events. To explore this question we are studying a range of different cellular and viral specimens using cryo-electron microscopy and tomography.

A particular emphasis of our research is the structure and life-cycle of asymmetric membrane viruses such as HIV. The assembly of the virus particles and their subsequent fusion with target cells offer insights into general features of vesicle budding and membrane fusion.

Cryo-electron microscopy techniques are particularly appropriate for studying vesicles and viruses because they allow membrane topology to be observed in the native state, while maintaining information about the structure and arrangement of associated proteins. Computational image processing and three-dimensional reconstructions are used to extract and interpret this information.

We take a step-by-step approach to understanding the native structure. Fluorescence microscopy can by used to locate and characterise features of interest. Three-dimensional reconstructions of these features can be obtained using cellular 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 cryo-electron microscopy and single particle reconstruction of purified complexes.

Future projects and goals

Our goal is to understand the interplay between protein assemblies and membrane shape. 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? What membrane topologies are involved in fusion of vesicles with target membranes? How does the curvature of a membrane influence its interaction with particular proteins? We will develop and apply microscopy and image processing approaches to such questions.