Professor David Owen

Structural biology of transport vesicle and organelle biogenesis

Uncovering the structural and molecular basis of membrane traffic along the endocytic pathway.

Transmembrane proteins are moved between organelles in transport vesicles, a process that is essential for eukaryotic cells. Defects in vesicle trafficking pathways lead to a wide range of pathophysiological effects. We take a combined structural and functional analyses approach to dissecting the mechanisms that control this process.

Cargo is sorted into the curved membrane of a forming vesicle and once membrane deformation is completed, the vesicle buds from the donor membrane. Subsequently it is transported to and then fuses with its target membrane. The protein coats that surround a transport vesicle possess self-assembly, membrane deformation and cargo recognition functions. Cargo selection is mediated by the direct binding of coat components to determinants in the cytosolic portions of transmembrane cargo. In endocytic clathrin-coated vesicles (CCVs), the most commonly used recognition motif determinants are YxxΦ and ExxxLL, which are recognised by the AP2 clathrin adaptor. Membrane deformation is achieved through a combination of the insertion of helices into the membrane bilayer and molecular crowding. In endocytic CCVs, the clathrin adaptor CALM plays a central role in this process along with AP2 and membrane-sculpting BAR-domain-containing proteins.

SNAREs are membrane-embedded proteins, which provide specificity and energy to transport vesicle-organelle fusion events. Appropriate SNAREs must be actively sorted into transport vesicles to allow the vesicles to fuse with their desired target organelle and also to return SNAREs that are required for subsequent vesicle transport events to their correct location. These recognition events, which occur in parallel with standard cargo selection, are mainly mediated by direct and highly specific recognition of the folded regions of SNAREs by vesicle coat components. In collaboration with other groups in CIMR and elsewhere, we investigate the structures and functions of proteins that control transport vesicle–organelle and organelle–organelle fusion through regulating SNARE-mediated membrane fusion activity, SNARE localization and membrane tethering events. One example of such a study is our work on the SNARE VAMP7 and its binding partner the retromer-coat-associated protein VARP.