Fig. 2: Zn²⁺ facilitates vesicle fusion in a reconstituted system.

a Single-vesicle content-mixing assay using two different types of vesicles (SV-vesicle and PM-vesicle). Fusion was monitored by measuring the fluorescence intensity of SRB encapsulated in SV-vesicle. b Normalized histograms of the fusion probability in the presence of 500 μM ions. c Corresponding cumulative probability of per minute upon ion injection in panel (b). Statistical significance was assessed by a two-tailed Student’s t test, compared to the case with Sr²⁺. d Normalized histograms of the probability of Zn²⁺-dependent fusion at various concentrations. e Corresponding cumulative probability per min upon Zn²⁺ injection in panel (d). Statistical significance was assessed by a two-tailed Student’s t test, compared to the case with 0 μM Zn²⁺. f Normalized histograms of Zn²⁺-dependent fusion probability with Syt1_WT and its mutants (Syt1-C2A*B*, Syt1-4A and Syt1-4W). g Corresponding cumulative probability per min upon Zn²⁺ injection in panel (f). In panels (c, e, and g), box plots and data points are shown for n (indicated below each box plot) independent repeat experiments. Statistical significance was assessed by a two-tailed Student’s t test, compared to the case with Syt1_WT. Box plots are defined as follows: the whiskers show the minimum and maximum values (excluding outliers), the box limits show the 25% and 75% percentiles, the center line denotes the median. Source data are provided as a Source Data file.