SNARE Zippering Is Suppressed by a Conformational Constraint that Is Removed by v-SNARE Splitting
Yinghui Liu,
Chun Wan,
Shailendra S. Rathore,
Michael H.B. Stowell,
Haijia Yu,
Jingshi Shen
Affiliations
Yinghui Liu
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309, USA; Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing 210023, China
Chun Wan
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309, USA
Shailendra S. Rathore
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309, USA
Michael H.B. Stowell
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309, USA
Haijia Yu
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309, USA; Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing 210023, China; Corresponding author
Jingshi Shen
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309, USA; Corresponding author
Summary: Intracellular vesicle fusion is catalyzed by soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs). Vesicle-anchored v-SNAREs pair with target membrane-associated t-SNAREs to form trans-SNARE complexes, releasing free energy to drive membrane fusion. However, trans-SNARE complexes are unable to assemble efficiently unless activated by Sec1/Munc18 (SM) proteins. Here, we demonstrate that SNAREs become fully active when the v-SNARE is split into two fragments, eliminating the requirement of SM protein activation. Mechanistically, v-SNARE splitting accelerates the zippering of trans-SNARE complexes, mimicking the stimulatory function of SM proteins. Thus, SNAREs possess the full potential to drive efficient membrane fusion but are suppressed by a conformational constraint. This constraint is removed by SM protein activation or v-SNARE splitting. We suggest that ancestral SNAREs originally evolved to be fully active in the absence of SM proteins. Later, a conformational constraint coevolved with SM proteins to achieve the vesicle fusion specificity demanded by complex endomembrane systems.
