The proposed research applies biophysical methods toward elucidating the underlying mechanism of Ca2+ triggered exocytosis of neurotransmitters during signal transmission at chemical synapses. Neurotransmitters (e.g., glutamate, GABA, catecholamine) within unstimulated neurons are sequestered within secretory vesicles docked at the plasma membrane of the presynaptic terminal. Upon the arrival of an action potential at the axon terminal, voltage-dependent calcium channels open and the resulting influx of calcium triggers a biochemical cascade that causes the neurotransmitter- containing vesicles to fuse to the plasma membrane, releasing their contents into the synaptic cleft. This process is mediated by SNARE proteins expressed on the plasma membrane and their counterparts on the vesicle's surface. Trans pairing of the neuronal v-SNARE (VAMP2) and t-SNAREs (syntaxin and SNAP-25) has been shown to form the essential molecular machinery necessary to induce vesicle fusion at the presynaptic terminal. The fusogenic function of the SNAREs is regulated by associated accessory molecules, including synaptotagmin and complexin. Although there have been considerable advances toward identifying the individual components of the fusion machinery in recent years, there is still numerous gaps in our understanding of SNARE-mediated membrane fusion and how the process is regulated. The central hypothesis of our research is that the interaction of the SNARE proteins generates a mechanical force that destabilizes the apposing membranes and thus lowers the energy requirement for membrane fusion. Calcium bound synaptotagmin promotes fusion by further lowering this energy requirement, whereas complexin inhibits fusion by preventing the SNARE complex from completely annealing. To test this hypothesis, the proposed research will employ state-of-the-art atomic force microscopy techniques to measure the force generated by the interactions of the cognate SNAREs. Results will determine if it is sufficient to bring the membranes to close proximity in order to initiate the SNARE-facilitated membrane fusion process. Moreover, we will determine by direct force measurements how the SNAREs, along with complexin and synaptotagmin, alter the energetics of the membrane fusion process, hence revealing the mechanism of SNARE- mediated membrane fusion.

Public Health Relevance

The proposed research applies biophysical methods toward elucidating the underlying mechanism of Ca2+ triggered exocytosis of neurotransmitters during signal transmission at chemical synapses of neural networks. The fundamental problem to be addressed is how do neurons regulate the fusion of vesicles with the plasma membrane. A detailed molecular understanding of Ca2+ triggered exocytosis is important because components of vesicle machinery are potential targets of many therapeutic reagents for a plethora of neurological disorders.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
Project #
Application #
Study Section
Biochemistry and Biophysics of Membranes Study Section (BBM)
Program Officer
Chin, Jean
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Miami School of Medicine
Schools of Medicine
Coral Gables
United States
Zip Code
Chu, Calvin; Celik, Emrah; Rico, Felix et al. (2013) Elongated membrane tethers, individually anchored by high affinity ?4?1/VCAM-1 complexes, are the quantal units of monocyte arrests. PLoS One 8:e64187
Celik, Emrah; Faridi, Mohd Hafeez; Kumar, Vinay et al. (2013) Agonist leukadherin-1 increases CD11b/CD18-dependent adhesion via membrane tethers. Biophys J 105:2517-27
Celik, Emrah; Abdulreda, Midhat H; Maiguel, Dony et al. (2013) Rearrangement of microtubule network under biochemical and mechanical stimulations. Methods 60:195-201
Celik, Emrah; Moy, Vincent T (2012) Nonspecific interactions in AFM force spectroscopy measurements. J Mol Recognit 25:53-6
Ziebarth, Noel M; Arrieta, Esdras; Feuer, William J et al. (2011) Primate lens capsule elasticity assessed using Atomic Force Microscopy. Exp Eye Res 92:490-4
Chivers, Claire E; Crozat, Estelle; Chu, Calvin et al. (2010) A streptavidin variant with slower biotin dissociation and increased mechanostability. Nat Methods 7:391-3
Jeney, Sylvia; Mor, Flavio; Koszali, Roland et al. (2010) Monitoring ligand-receptor interactions by photonic force microscopy. Nanotechnology 21:255102
Abdulreda, Midhat H; Moy, Vincent T (2009) Investigation of SNARE-Mediated Membrane Fusion Mechanism Using Atomic Force Microscopy. Jpn J Appl Phys (2008) 48:8JA03-8JA0310
Abdulreda, Midhat H; Bhalla, Akhil; Rico, Felix et al. (2009) Pulling force generated by interacting SNAREs facilitates membrane hemifusion. Integr Biol (Camb) 1:301-10