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IRTG / Soft Matter Science
Freiburger Materialforschungszentrum
Stefan-Meier-Str. 21
79104 Freiburg, Germany

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You are here: Home Events Dr. Erdem Karatekin "Controlling secretion via fusion pore dynamics and pre-synaptic membrane mechanics"

Dr. Erdem Karatekin "Controlling secretion via fusion pore dynamics and pre-synaptic membrane mechanics"

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Cellular & Molecular Physiology, Nanobiology Institute, Yale University, New Haven, CT, USA

What
  • Seminar
When Jun 06, 2019
from 09:15 AM to 10:00 AM
Where Seminarraum A, FMF, Stefan-Meier-Str. 21, Freiburg
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Calcium-triggered release of neurotransmitters and hormones underlie neuronal communication and physiological regulation. Cargo release requires expansion of the initial, nanometer-sized fusion pore connecting a cargo-laden vesicle and the cell membrane. Pore dynamics contribute to release kinetics and determine the mode of vesicle recycling, but mechanisms are poorly understood. We developed an approach to monitor single fusion pores with biochemically defined components to characterize such mechanisms. Release requires neuronal/exocytic v- and t-SNARE proteins to form complexes bridging the fusing membranes. We fuse nanodiscs reconstituted with v-SNARE proteins with engineered cells expressing cognate t-SNAREs in a flipped topology. Fusion results in a pore that connects the cytoplasm to the exterior, allowing single-pore conductance measurements under voltage-clamp. We found pore formation requires only a few SNARE complexes, but pore expansion relies on many more. The calcium-sensor Synaptotagmin-1 contributes to pore expansion using the SNARE complex as a calcium-dependent lever.

Another important factor regulating synaptic transmission and hormone release is membrane tension. Increased tension promotes fusion pore dilation and strongly inhibits endocytosis, while decreased tension leads to transient pores and facilitates endocytosis. It has been proposed that a reduction in tension due to exocytic membrane addition to the presynaptic terminal surface could provide a mechanism that couples exo- and endocytosis. Such a coupling implies membrane flow from an exocytic site to an endocytic one, but such flows have never been demonstrated, and so the relationship between synaptic vesicle and tension dynamics is unknown. Using optical tweezers to pull thin membrane tethers from pre-synaptic membranes, we show that membrane flow and tension equilibration at the presynaptic plasma membrane is exceptionally facile, likely tuned for rapid turnover of synaptic vesicles.

invited by Prof. Jan Behrends

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