title: Stability, folding dynamics, and long-range conformational transition of the synaptic t-SNARE complex.
abstract: 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 kBis 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.
authors.affiliation: Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520.
authors.forename: Xinming
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520.|Integrated Graduate Program in Physical and Engineering Biology, Yale University, New Haven, CT 06511.|Department of Physics, Yale University, New Haven, CT 06511.|Nanobiology Institute, Yale University, West Haven, CT 06477.
authors.forename: Aleksander A
authors.initials: AA
authors.lastname: Rebane
authors.affiliation: Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520.
authors.forename: Lu
authors.initials: L
authors.lastname: Ma
authors.affiliation: Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520.|Nanobiology Institute, Yale University, West Haven, CT 06477.
authors.forename: Feng
authors.initials: F
authors.lastname: Li
authors.affiliation: Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520.|Integrated Graduate Program in Physical and Engineering Biology, Yale University, New Haven, CT 06511.
authors.forename: Junyi
authors.initials: J
authors.lastname: Jiao
authors.affiliation: Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520.
authors.forename: Hong
authors.initials: H
authors.lastname: Qu
authors.affiliation: Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520.|Nanobiology Institute, Yale University, West Haven, CT 06477.|Laboratoire de Physique Statistique, École Normale Superieure, L'université de recherche Paris Sciences et Lettres, CNRS UMR 8550, Sorbonne Universités, Université Pierre-et-Marie-Curie University of Paris 06, Université Paris Diderot, 75005 Paris, France.
authors.forename: Frederic
authors.initials: F
authors.lastname: Pincet
authors.affiliation: Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520.|Nanobiology Institute, Yale University, West Haven, CT 06477.
authors.forename: James E
authors.initials: JE
authors.lastname: Rothman
authors.affiliation: Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520; yongli.zhang@yale.edu.
authors.forename: Yongli
authors.identifier: 0000-0001-5424-3022
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D008561:Membrane Fusion; D051379:Mice; D018625:Microscopy, Atomic Force; D056004:Molecular Dynamics Simulation; D051938:Munc18 Proteins / Q000737:chemistry / Q000502:physiology; D052898:Optical Tweezers; D011487:Protein Conformation; D000072417:Protein Domains; D017510:Protein Folding; D055550:Protein Stability; D050765:Qa-SNARE Proteins / Q000737:chemistry / Q000502:physiology; D050600:SNARE Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology; D050825:Synaptosomal-Associated Protein 25 / Q000737:chemistry / Q000502:physiology; D050988:Vesicle-Associated Membrane Protein 2 / Q000737:chemistry / Q000502:physiology
chemical_list: D051938:Munc18 Proteins; D050765:Qa-SNARE Proteins; D050600:SNARE Proteins; C494209:Snap25 protein, mouse; D050825:Synaptosomal-Associated Protein 25; D050988:Vesicle-Associated Membrane Protein 2; C494808:vesicle-associated membrane protein 2, mouse
keywords: SNARE assembly; SNARE four-helix bundle; membrane fusion; optical tweezers; t-SNARE complex