Our research focuses on elucidating the mechanisms of neurotransmitter release by calcium-triggered synaptic vesicle exocytosis and of intracellular membrane fusion in general. We also investigate how release is regulated in presynaptic plasticity processes that underlie diverse forms of information processing in the brain. We use a wide variety of biophysical techniques in combination with reconstitution approaches. Long-term collaborations with Thomas Sudhof and Christian Rosenmund constitute a key aspect of our overall strategy, allowing correlation of physiological and structural data. We also collaborate closely with Diana Tomchick and Qiu-Xing Jiang, whose expertise in X-ray crystallography and electron microscopy, respectively, complements the experience of the Rizo lab in NMR spectroscopy.|
Together with results from other groups, advances made by our lab allowed us to reconstitute synaptic vesicle fusion with the eight most central components of the release machinery, namely the SNAREs syntaxin-1, synaptobrevin and SNAP-25, NSF, a-SNAP, the SM protein Munc18-1, and core fragments of Munc13-1 and synaptotagmin-1(1). In our current working model (on the right), syntaxin-1 (yellow), SNAP-25 (green) and synaptobrevin (red) form a four-helix bundle called the SNARE complex that brings the membranes together and is key for membrane fusion. This complex is disassembled by NSF and a-SNAP (not shown) to recycle the SNAREs for another round of fusion. Munc18-1 (pink) binds tightly to syntaxin-1, which initially adopts a self-inhibited ‘closed conformation’. Together with the MUN domain of Munc13-1 (brown), Munc18-1 helps to orchestrate SNARE complex formation in a manner that is not disrupted by NSF and a-SNAP. Synaptotagmin-1 (blue) binds to the SNARE complex and helps to bring the vesicle and plasma membranes together in a calcium-dependent manner, thus cooperating in membrane fusion.
Current efforts are directed at testing this model, determining the structures of macromolecular assemblies including the SNAREs and other proteins, and investigating how regulatory proteins such as complexins and RIMs modulate neurotransmitter release.