One of Axel Brunger's major goals is to decipher the molecular mechanisms of synaptic neurotransmitter release by conducting single-molecule/particle reconstitution and imaging experiments, combined with high-resolution structural studies of the synaptic vesicle fusion machinery. A second goal is to develop advanced biomolecular imaging methods at the molecular scale.
Studies of Synaptic Vesicle Fusion with a Synthetic System
Neuronal communication is made possible by the release of neurotransmitters, which in turn depends on the fusion of neurotransmitter-laden synaptic vesicles at the ends of nerve cells. Synaptic vesicle fusion is triggered by an influx of Ca2+ ions into the neuron upon depolarization of the neuron, a process that initiates neurotransmission. Neurotransmitter release is quantized, that is, at most, one synaptic vesicle fuses in the active zone upon an action potential. This process is controlled by several proteins, including SNAREs (soluble NSF [N-ethylmaleimide-sensitive factor] attachment protein receptors), the Ca2+sensor synaptotagmin 1, Munc18, complexin, and the ATPase NSF, among others. Thus, neurotransmitter release is a biological phenomenon controlled by complex interactions between individual molecules. An understanding of the underlying molecular mechanisms requires methods that are capable of observing single vesicles and molecules.
Our approach to understanding the molecular basis for neurotransmitter release consists of a combination of structural and biophysical studies of in vitro systems. Structural information about complexes between the individual molecular components is primarily obtained by X-ray crystallography and single-molecule FRET (fluorescence resonance energy transfer) measurements; information about membrane morphology is obtained by cryo-electron microscopy.This hybrid approach provides the framework for investigations targeted at the functional and dynamic aspects of the system, using single-molecule and single-particle fluorescence microscopy techniques.
Diao et al., eLife, 2013, DOI:10.7554/eLife.00592; Diao et al., eLife, 2012, DOI:10.7554/eLife.00109