Journal Article

Stability, folding dynamics, and long-range conformational transition of the synaptic t-SNARE complex

Jiao, Junyi, Pincet, Frederic, Ma, Lu, Rothman, James E., Rebane, Aleksander A., Zhang, Yongli, Li, Feng(李峰), Qu, Hong, Zhang, Xinming

2016

Overview

Synaptic soluble N-ethylmaleimide–sensitive factor attachment protein receptors (SNAREs) couple their stepwise folding to fusion of synaptic vesicles with plasma membranes. In this process, three SNAREs assemble into a stable four-helix bundle. Arguably, the first and rate-limiting step of SNARE assembly is the formation of an activated binary target (t)-SNARE complex on the target plasma membrane, which then zippers with the vesicle (v)-SNARE on the vesicle to drive membrane fusion. However, the t-SNARE complex readily misfolds, and its structure, stability, and dynamics are elusive. Using single-molecule force spectroscopy, we modeled the synaptic t-SNARE complex as a parallel three-helix bundle with a small frayed C terminus. The helical bundle sequentially folded in an N-terminal domain (NTD) and a C-terminal domain (CTD) separated by a central ionic layer, with total unfolding energy of ∼17 kBT, where kB is the Boltzmann constant and T is 300 K. Peptide binding to the CTD activated the t-SNARE complex to initiate NTD zippering with the v-SNARE, a mechanism likely shared by the mammalian uncoordinated-18-1 protein (Munc18-1). The NTD zippering then dramatically stabilized the CTD, facilitating further SNARE zippering. The subtle bidirectional t-SNARE conformational switch was mediated by the ionic layer. Thus, the t-SNARE complex acted as a switch to enable fast and controlled SNARE zippering required for synaptic vesicle fusion and neurotransmission.

• Publisher: National Academy of Sciences
• Subject: Amino Acid Sequence / Animals / Biological Sciences / Biophysics and Computational Biology / Membrane Fusion / Membranes / Mice / Microscopy, Atomic Force / Molecular Dynamics Simulation / Munc18 Proteins - chemistry / Munc18 Proteins - physiology / Optical Tweezers / Peptides / Plasma / PNAS Plus / Protein Conformation / Protein Domains / Protein Folding / Protein Stability / Proteins / Qa-SNARE Proteins - chemistry / Qa-SNARE Proteins - physiology / SNARE Proteins - chemistry / SNARE Proteins - genetics / SNARE Proteins - physiology / Spectrum analysis / Synaptic Transmission - physiology / Synaptosomal-Associated Protein 25 - chemistry / Synaptosomal-Associated Protein 25 - physiology / Vesicle-Associated Membrane Protein 2 - chemistry / Vesicle-Associated Membrane Protein 2 - physiology