Synaptic vesicle fusion

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The Synaptic vesicle fusion is the membrane fusion of synaptic vesicles with the presynaptic membrane . It describes functional and structural changes in synaptic connections (“ synaptic plasticity ”), which are seen as the basis for the learning processes of memory. The molecular structure, structure and processes are important for understanding the neuronal development of synapses. These are formed by asymmetrical connections between two specialized membranes . There is a presynaptic, active zone where the vesicles filled with neurotransmitters fuse , while signals are picked up from the opposite postsynaptic zone via transmitter receptors .

functionality

Fast and reliable signal transmission between the nerve cells via the synaptic gap is the basis of a functioning brain . Two nerve cells approach a synapse in order to exchange signals.

The “sending” cell releases a transmitter substance, the “receiving” cell then generates a new signal by generating an action potential . Genetic analyzes have shown that matrix proteins from different families play an important role in vesicle fusion in the active zone . These proteins contribute to the stable construction of the synapses. Vesicle fusion is mediated by SNARE proteins . Investigations with a STED (Stimulated Emission Depletion) microscope enabled researchers from the Max Planck Society to visualize proteins from individual synaptic vesicles in detail. In this way they were able to make the protein synaptotagmin , which is located in the membrane of the vesicles, visible. Synaptic vesicles are membrane vesicles around 40 nanometers in size that are filled with neurotransmitters. They transport these messenger substances to the contact points between two nerve cells and pass them on to the synapse by fusing with the membrane of the nerve cell. It was demonstrated that the proteins or synaptotagmin molecules contained in the membrane of the vesicles, which are partly responsible for error-free neurocommunication , for example , remain connected to one another after the fusion on the nerve membrane. The proteins released into the membrane can then be taken up again.

The neuronal vesicles prefer the “active zones” to pass on their messenger substances, whereby the scaffold protein Bruchpilot (BRP), discovered in fruit flies , makes a decisive contribution to the development of these active zones. The vesicle fusion depends on the BRP level in the active zone. The higher this level, the greater the likelihood that the zone will be involved in a synaptic vesicle fusion. The protein spinophilin or PI4KIIIα also appears to be important for evoked vesicle fusion. In addition to the proteins, the lipid composition of the plasma membrane also has an impact on synaptic transmission and the probability of fusion.

An influx of calcium ions through the calcium channels triggers a complete fusion of the synaptic vesicle with the presynaptic membrane. The SNARE proteins synaptobrevin , syntaxin and SNAP-25 are particularly involved in this fusion . They form a twisted structure that fuses the vesicles with the presynaptic membrane so that the neurotransmitters are released into the synaptic cleft. If calcium ions are bound to Synaptotagmin, they act as a trigger for the release of neurotransmitters. Complexin , on the other hand, triggers a counter-regulation, a mechanism that prevents membrane fusion and thus the exocytosis of neurotransmitters.

literature

Web links

Individual evidence

  1. ↑ Rui Tian: Structural and functional organization of synaptic proteins in Drosophila melanogaster . Ed .: University of Würzburg Medical Faculty. Institute for Clinical Neurobiology. Würzburg 2011 (English, uni-wuerzburg.de - dissertation).
  2. ↑ Christina Beis: The Role of Molecular Scaffolds at the Active Zone in Synaptic Vesicle Distribution and Release Probability . Berlin December 22, 2016 ( fu-berlin.de ).
  3. ↑ How neurotransmitters are released at synapses . In: Deutsches Ärzteblatt . September 15, 2017 ( aerzteblatt.de ).
  4. ↑ Vera Zylka-Menhorn, Nicola Siegmund-Schultze: Nobel Prize Medicine and Physiology: How a Molecule Arrives at its Destination at the Right Time . In: Deutsches Ärzteblatt . 2013 ( aerzteblatt.de ).