Biophysical Society Conference | Estes Park 2023

Membrane Budding and Fusion

Wednesday Speaker Abstracts

DYNAMIN PRIME - ACCELERATING ENDOCYTOSIS AT SYNAPSES

Shigeki Watanabe ; 1 Johns Hopkins University, Cell Biology, Baltimore, MD, USA

Dynamin mediates fission of vesicles during endocytosis. During clathrin-mediated endocytosis, recruitment of dynamin from the cytosol to endocytic pits takes tens of seconds. However, for synaptic vesicle endocytosis, dynamin must be recruited to the site of endocytosis on the order of milliseconds to mediate ultrafast endocytosis. However, the mechanism underlying such rapid recruitment is unknown. Here, we demonstrate that Dynamin 1 is enriched at endocytic sites prior to the initiation of ultrafast endocytosis. Specifically, Dynamin 1xA, a splice variant of Dynamin 1, interacts with Syndapin 1 to form molecular condensates on the plasma membrane. Single-particle tracking of Dynamin 1xA molecules confirms the liquid-like property of condensates with a small immobile fraction of molecules. Time-resolved electron microscopy by flash-and-freeze suggests that loss of Dynamin 1 causes an accumulation of endocytic pits on the plasma membrane; the base of these pits is wide-open, suggesting that Dynamin 1 is potentially involved from the early stage of ultrafast endocytosis. Over expression of Dynamin 1xA, but not another splice variant xB, rescues this defect. When binding of Dynamin 1xA to Syndapin 1 is dirupted, Dynamin 1xA cannot form condensates. Likewise, when Syndapin 1 binding to Dynamin 1 is disrupted, Dynamin 1xA becomes diffuse. Interestingly, disrupting Syndapin 1 interaction with the plasma membrane also leads to diffuse localization of Dynamin 1xA, suggesting that Syndapin 1 likely acts as a hub. When Dynamin 1xA is diffusely localized, ultrafast endocytosis is slowed. Thus, Dynamin 1xA condensates concentrate Dynamin 1xA at the sites of endocytosis to bypass the recruitment phase and accelerate endocytosis.

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