Munc18-1 binding to the neuronal SNARE complex controls synaptic vesicle priming |
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Authors: | Ferenc Deák Yi Xu Wen-Pin Chang Irina Dulubova Mikhail Khvotchev Xinran Liu Thomas C Südhof Josep Rizo |
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Institution: | 1.Howard Hughes Medical Institute, 2.Department of Neuroscience, 3.Department of Biochemistry, 4.Department of Pharmacology, and 5.Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390 |
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Abstract: | Munc18-1 and soluble NSF attachment protein receptors (SNAREs) are critical for synaptic vesicle fusion. Munc18-1 binds to the SNARE syntaxin-1 folded into a closed conformation and to SNARE complexes containing open syntaxin-1. Understanding which steps in fusion depend on the latter interaction and whether Munc18-1 competes with other factors such as complexins for SNARE complex binding is critical to elucidate the mechanisms involved. In this study, we show that lentiviral expression of Munc18-1 rescues abrogation of release in Munc18-1 knockout mice. We describe point mutations in Munc18-1 that preserve tight binding to closed syntaxin-1 but markedly disrupt Munc18-1 binding to SNARE complexes containing open syntaxin-1. Lentiviral rescue experiments reveal that such disruption selectively impairs synaptic vesicle priming but not Ca2+-triggered fusion of primed vesicles. We also find that Munc18-1 and complexin-1 bind simultaneously to SNARE complexes. These results suggest that Munc18-1 binding to SNARE complexes mediates synaptic vesicle priming and that the resulting primed state involves a Munc18-1–SNARE–complexin macromolecular assembly that is poised for Ca2+ triggering of fusion. |
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