Observation of Two-Step Unzipping of a Single SNARE Complex by using Nano-Mechanical Measurement

Abstract

Soluble NSF Attachment Protein Receptors (SNARE) complex is known as the minimal machinery for synaptic vesicle exocytosis in neuronal communication. The conformational transition from “trans” to “cis” form of SNARE complex is an essential step of a Ca2+ triggered vesicle fusion to release neurotransmitters. Until recently, it has been debated whether the trans-SNARE complex is fully-zipped or partially-zipped before transition toward cis-form. We observe from nano-mechanical measurement by magnetic tweezer that a single soluble SNARE complex shows a sequential two-step unzipping, about 10nm each. It implies that trans-SNARE complex could be partially-zipped when force is applied like the hydration force between lipid bilayers. Other neuronal proteins might act on the unzipped domain to clamp trans-SNARE complex before conformational transition to cis-SNARE complex.