Synaptotagmin Expands Membrane Fusion Pore by Facilitating SNARE-Complex Formation

Abstract

Pore expansion, an essential step for SNARE-mediated membrane fusion, has not been well studied due to the lack of a reliable content mixing assay. Recently, we have developed a new assay to detect the inter-vesicular mixing of large cargoes at the size of several nanometers at the single molecule and vesicle level [1]. Through our new assay, we found that the neuronal SNARE complexes alone, without regulatory proteins, are able to expand fusion pore inefficiently. By interacting with t-SNARE proteins through a trans-conformer [2], membrane anchor synaptotagmin 1 and Ca2+ facilitate SNARE complex formation for fusion pore expansion.