Our research focuses on investigating the molecular mechanism of neurotransmitter release by calcium-triggered synaptic vesicle exocytosis. We use a wide variety of biophysical techniques in combination with reconstitution approaches. Collaborations with Thomas Sudhof, Christian Rosenmund and other neurobiologists allow us to correlate our in vitro studies with physiological data, while collaborations with Diana Tomchick, Daniela Nicastro and Xiaochen Bai enable us to pursue studies by X-ray crystallography and cryo-EM microscopy, complementing the expertise of Josep Rizo in NMR spectroscopy. The importance of this research was highlighted when Thomas Sudhof was awarded the 2013 Nobel Prize in Physiology or Medicine, which he shared with James Rothman and Randy Schekman.
Together with results from other groups, advances made by our lab allowed us to reconstitute synaptic vesicle fusion with the most central components of the neurotransmitter release machinery and to develop a model that assigns defined functions to these components [1-5] (see diagrams on the right). In this model, the core of the membrane fusion apparatus is formed by the SNAREs syntaxin-1, synaptobrevin and SNAP-25, which form a tight SNARE complex that brings the vesicle membranes together, as well as by Munc18-1 and Munc13-1, which orchestrate SNARE complex assembly. Other crucial proteins are NSF and alpha-SNAP, which disassemble the SNARE complex, and the Ca2+ sensor synaptotagmin-1, which binds to membranes and to the SNARE complex in a tight interplay with complexins (NSF, alphaSNAP and complexin are not shown in the diagrams). Despite this wealth of information, we still do not know how these proteins are arranged to trigger fast, calcium-dependent membrane fusion and how they apply force to the membranes to trigger fusion.
Our research is in a very exciting moment because we believe that we will be able to address these fundamental questions and elucidate the basic mechanism of neurotransmitter release in a near future, building on our reconstitution studies and capitalizing on constant improvements in the techniques available for structural determination. Current efforts to achieve this goal include structural studies of macromolecular assemblies between two membranes using cryo-EM and NMR spectroscopy on nanodiscs. We also continue to use X-ray crystallography to solve the structures of soluble complexes and reconstitution approaches to incorporate additional key components of the release machinery such as CAPS, RIMs and Rab3s. As we make progress in understanding the basic mechanism of release, including these and other regulators will be crucial to elucidate how the release probability is modulated in a wide variety of presynaptic plasticity processes that shape the properties of neural networks and underlie diverse forms of information processing in the brain.
If you want to learn more details about our research, you can go to the pages on the Core machinery, Regulation of release and Calcium sensing.
1. Ma et al. (2013) Science 339, 421-425.
2. Liu et al. (2016) eLife 5, e13696.
3. Xu et al. (2017) eLife 6, e22567.
4. Sitarska et al. (2017) eLife, e24278.
5. Rizo (2018) Protein Sci., in press.