Structural studies of proteins involved in vesicle fusion

The evolutionarily conserved SNARE (SNAP receptor) proteins and their complexes are key players in the docking and fusion of vesicles with their target membrane. Upon fusion the vesicle cargo enters the space on the other side of the target membrane. This process plays a fundamental role in such diverse processes as neurotransmission and protein secretion. Our recent work has revealed remarkable conservation of biophysical properties of the SNARE proteins. SNARE proteins are largely unstructured or only partially structured when studied individually in vitro. Upon binary and ternary complex formation, significant amount of structure is induced as evidenced by circular dichroism, nuclear magnetic resonance spectroscopy, endogenous tryptophan fluorescence, and ANS binding. Associated with SNARE ternary complex formation is a more than 20 degree increase in protein melting temperature. One can speculate that the energy released by complex formation could be used to drive membrane fusion by overcoming the repulsion between solvated lipid bilayers. Recent structural and biophysical studies of the SNARE proteins will be presented.