Research interests

Physiological processes such as neurotransmission and the regulation of the blood glucose level require the release of neurotransmitters and insulin in a spatially and temporally controlled manner. A cascade of reactions and a series of protein interactions control the stepwise assembly of the fusion machinery. The first step is the interaction of secretory vesicles with the plasma membrane, which is mediated by compartment-specific tethering proteins. These proteins determine where fusion occurs. The tethers together with other regulatory components control the subsequent assembly of the fusion machinery. The fusion machinery consists of compartment-specific v-SNAREs localized on secretory vesicles, which pair with cognate t-SNAREs on the plasma membrane. SNARE complexes assemble in a stepwise fashion and distinct regulators either accelerate or arrest the formation of intermediates. This assembly line creates distinct pools of vesicles with different release probabilities. Finally, a sensor that is directly coupled to the fusion machinery recognizes the incoming signal and triggers membrane fusion/fusion pore opening. This signal transduction event determines when vesicle fusion occurs. Our goal is to reveal how the molecular fusion machinery assembles and controls regulated exocytosis and fusion pore dynamics. We study the role of defined regulators at distinct steps of the assembly pathway. To indentify novel regulators, cellular extracts (e.g. cytosol) are added to reconstituted fusion assays. To obtain structutal information, we are collaborating with other laboratories in Heidleberg.


Methods applied

Mechanistic insights are obtained by reconstituting membrane fusion using recombinant proteins and liposomes. In addition, we study the fusion properties of purified secretory vesicles such as synaptic vesicles. Fusion is measured in biochemial assays and in the microscope by analyzing content and lipid mixing of single vesicles. These in vitro studies are complemented by in vivo assays monitoring single vesicle fusion using the pH-sensitive GFP - pHluorin. "