Biophysical Society Conference | Estes Park 2023

Membrane Budding and Fusion

Poster Abstracts

51-POS Board 17 DO CHAPERONES REGULATE THE QUANTAL SIZE DURING EXOCYTOSIS? Debasis Das 1 ; 1 Tata Institute of Fundamental Research, Biological Sciences, Mumbai, India The ‘holy grail’ in the study of membrane trafficking is the actual fusion reaction, in which secretory vesicles fuse with the plasmalemma to form the fusion pores. These pores are the first aqueous connection between the lumen of secretory vesicles and the extracellular space. During cell-to-cell communication, chemical messengers secrete through these pores in a tightly regulated manner. The process gets altered under disease conditions where too little, or, too much secretion occurs. Fusion pores are the sites of action of several regulatory factors, known to either stimulate or limit neurotransmitter secretion. During membrane fusion, multiple SNARE complexes assemble at the release site, leading to fusion pore opening. We ask the question - of whether the fusion pore itself can regulate the quantal size during vesicular secretion. We have used single molecule biophysics, ensemble biochemistry and cell based techniques to study the role of SNARE chaperones Munc13-1 and Munc18-1 in organizing fusion pore assembly at the release site. We have used a recently developed nanodisc (ND)-black lipid membrane (BLM) technique to demonstrate that the Munc proteins rescue fusion pores from the phorbol ester mediated inhibitory state. These SNARE chaperones differentially affect SNARE complex clustering at the onset of membrane fusion. When both the Munc proteins are present simultaneously, they alter size and kinetic properties of individual nascent fusion pores. Hence, SNARE chaperones can modulate the amount of chemical messengers’ release, by directly modulating fusion pore conformations, which has a significant impact in cell to cell communication.

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