Abstract
The core mechanism of intracellular vesicle fusion consists of SNAREpin zippering between vesicular and target membranes. Recent studies indicate that the same SNARE-binding protein, complexin (CPX), can act either as a facilitator or as an inhibitor of membrane fusion, constituting a controversial dilemma. Here we take energetic measurements with the surface force apparatus that reveal that CPX acts sequentially on assembling SNAREpins, first facilitating zippering by nearly doubling the distance at which v- and t-SNAREs can engage and then clamping them into a half-zippered fusion-incompetent state. Specifically, we find that the central helix of CPX allows SNAREs to form this intermediate energetic state at 9-15 nm but not when the bilayers are closer than 9 nm. Stabilizing the activated-clamped state at separations of less than 9 nm requires the accessory helix of CPX, which prevents membrane-proximal assembly of SNAREpins.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adaptor Proteins, Signal Transducing / chemistry
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Adaptor Proteins, Signal Transducing / metabolism
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Adaptor Proteins, Signal Transducing / physiology*
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Adaptor Proteins, Vesicular Transport / chemistry
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Adaptor Proteins, Vesicular Transport / metabolism
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Adaptor Proteins, Vesicular Transport / physiology
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Animals
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Binding Sites
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Humans
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Lipid Bilayers / metabolism
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Membrane Fusion / physiology
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Mice
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Models, Molecular
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Nerve Tissue Proteins / chemistry
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Nerve Tissue Proteins / metabolism
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Nerve Tissue Proteins / physiology
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Protein Structure, Tertiary
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Rats
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SNARE Proteins / chemistry*
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SNARE Proteins / metabolism
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SNARE Proteins / physiology
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Synaptosomal-Associated Protein 25 / chemistry
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Synaptosomal-Associated Protein 25 / metabolism
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Synaptosomal-Associated Protein 25 / physiology
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Syntaxin 1 / chemistry
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Syntaxin 1 / metabolism
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Syntaxin 1 / physiology
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Vesicle-Associated Membrane Protein 2 / chemistry
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Vesicle-Associated Membrane Protein 2 / metabolism
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Vesicle-Associated Membrane Protein 2 / physiology
Substances
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Adaptor Proteins, Signal Transducing
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Adaptor Proteins, Vesicular Transport
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CPLX3 protein, human
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Lipid Bilayers
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Nerve Tissue Proteins
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SNARE Proteins
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Snap25 protein, mouse
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Stx1a protein, rat
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Synaptosomal-Associated Protein 25
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Syntaxin 1
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Vesicle-Associated Membrane Protein 2
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complexin I
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vesicle-associated membrane protein 2, mouse