A Dynamin Homolog Promotes the Transition from Hemifusion to Content Mixing in Intracellular Membrane Fusion

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Dynamin family members have been implicated in exocytosis. Vps1 (the yeast dynamin homolog) mutant vacuoles show decreased fusion and trans-Soluble N-ethylmaleimide sensitive factor Attachment Protein Receptor (SNARE) complex formation but comparable hemifusion relative to wild type. Vps1, through its oligomerization and SNARE-domain binding, brings together multiple t-SNAREs. This finding uncovers a novel function of Vps1 in coordinating the hemifusion – content mixing transition in yeast vacuole fusion.

The convergence of the antagonistic reactions of membrane fusion and fission at the hemifusion/hemifission intermediate has generated a captivating enigma of whether SolubleN-ethylmaleimide sensitive factor Attachment Protein Receptor (SNAREs) and dynamin have unusual counter-functions in fission and fusion, respectively. SNARE-mediated fusion and dynamin-driven fission are fundamental membrane flux reactions known to occur during ubiquitous cellular communication events such as exocytosis, endocytosis and vesicle transport. Here we demonstrate the influence of the dynamin homolog Vps1 (Vacuolar protein sorting 1) on lipid mixing and content mixing properties of yeast vacuoles, and on the incorporation of SNAREs into fusogenic complexes. We propose a novel concept that Vps1, through its oligomerization and SNARE domain binding, promotes the hemifusion-content mixing transition in yeast vacuole fusion by increasing the number oftrans-SNAREs.

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