Fig. 3: Cryo-ET of synaptic vesicle fusion states.

a–c Schematic illustrations with details about size measurements (a), exemplary cryo-ET slices (b), and isosurfaces (c) of 7 categories of membrane rearrangements observed at synaptic active zones of stimulated neurons. Scare bars: 20 nm. d Fractions of synapses with or without membrane rearrangements in stimulated and stimulated, TTX-treated samples. Fisher’s exact test (stimulated vs. stimulated, TTX for all 8 categories) p = 0.007; Fisher’s exact test with Benjamini-Hochberg correction for multiple comparisons (no membrane rearrangements vs. stalk formation, stimulated vs. stimulated, TTX) p = 0.035. e Fractions of synapses without membrane rearrangements, ongoing fusion, or bumps in stimulated and stimulated, TTX-treated samples. Synapses were counted as “ongoing fusion” if at least one stalk formation, closed, open, dilated, or collapsing fusion pore was observed. Fisher’s exact test p < 0.001. d, e Stimulated sample: N = 75 synapses from 3 grids and 2 independent freezings, TTX sample: N = 28 synapses from 1 grid. f Fractions of individual fusion states in stimulated synapses. N = 55 fusion events. g Snapshot of a coarse-grained simulation of an SV approaching the active zone membrane, with particle-based representation of recruiting tethers, SNARE proteins and varying copy numbers of proteins inducing membrane curvature at the active zone below the SV. h Time evolution of the vertical distance between SV and active zone membrane, depending on the copy number of membrane curvature-inducing proteins. Source data are provided as a Source Data file.