Structural Biology

Biography

Biography: Maria Bykhovskaia

Abstract

Neuronal transmitters are released via the fusion of synaptic vesicles with the plasma membrane. Vesicles dock to the membrane via a protein complex termed SNARE, which contains membrane attached (t-SNARE) and vesicle attached (v-SNARE) proteins. The fusion occurs in response to a calcium inflow, and the vesicle protein Synaptotagmin (Syt) serves as a calcium sensor. A cytosolic protein Complexin (Cpx) interacts with the SNARE complex, restricting the spontaneous fusion. Although molecular interactions of these proteins have been extensively studied, it is still debated how Syt dynamically interacts with the SNARE protein complex, Cpx, and lipid bilayers to trigger lipid merging. To elucidate these mechanisms, we combined molecular dynamics (MD) simulations with molecular biology and genetic approaches in Drosophila. Basing on MD simulations, we created a model of the protein fusion machinery wherein Cpx dynamically interacts with v-SNARE, preventing full SNARE assembly. Our MD simulations also elucidated how Syt interacts with lipid bilayers, causing lipid bulging that may precede the formation of the stalk and the fusion pore opening. Finally, our simulations predicted direct interactions of Syt with the SNARE-bound Cpx. The developed molecular model enabled us to predict new mutations in v-SNARE and Cpx that alter the fusion process. To test these predictions, we generated Drosophila lines with single point mutations and investigated how these mutations affect  the kinetics of transmitter release. The results of these experiments suggest that our model creates the basis for systematic approach to manipulating the fusion machinery based on theoretical predictions derived from MD simulations.

References:

1. Feliciano P., H. Matos, R. Andrade, and M. Bykhovskaia. 2017. Synapsin II regulation of GABAergic synaptic transmission is dependent on interneuron subtype. J. Neurosci. doi: 10.1523/JNEUROSCI.0844-16.2016.
2. Sabeva N., Cho. R., Vasin, A. Gonzalez, J.T. Littleton, and M. Bykhovskaia. (2016) Complexin Mutants Reveal Partial Segregation Between Recycling Pathways that Drive Evoked and Spontaneous Neurotransmission J Neurosci 3:383-396.
3. Vasin, A., Volfson, D., Littleton, J. T., and Bykhovskaia, M. (2016) Interaction of the Complexin Accessory Helix with Synaptobrevin Regulates Spontaneous Fusion, Biophys J 111, 1954-1964.
4. Byhhovskaia M. 2015. Calcium binding promotes conformation flexibility of neuronal calcium sensor Synaptotagmin 1. Biophys. J. 108:22507-20.
5. Fourtoul, N., Singh P., Hui C.Y., Bykhovskaia M., and A. Jagota. 2015. Coarse-Grained Model of the Snare Complex Determines the Number of Snares Required for Docking. Biophys. J. 108:2258-69.