Fig. 5: Syt7 enhances Ca²⁺-synchronized fusion under elevated [Ca²⁺]_basal conditions.

a Comparison of the Ca²⁺ (100 µM) evoked fusion characteristics without (green) or with (pink) 0.5 μM [Ca²⁺]_basal included during vesicle docking reveals that when pre-activated, Syt7 (included in the bilayer at 1:200 protein-to-lipid ratio) increases the proportion of Ca²⁺-coupled release of Syt1-containing vesicles (Syt1^WT/Syt7^WT) without changing the overall fusion levels. This enhancement was not observed with Syt1^WT alone. Notably, a similar degree of enhancement of Ca²⁺-synchronized release was observed with vesicles containing Ca²⁺-binding deficient Syt1^DA (Syt1^DA/Syt7^WT). Data (mean ± standard deviation) are from 5 independent experiments (N = 5) for each condition (~40–50 vesicles per experiment). Complexin (2 µM) in solution was included in all experiments. b The dual Syt1/Syt7 clamp model, incorporating the delayed release of the clamp for Syt7, reproduces the experimentally observed enhancement of synchronous release following pre-activation with low micromolar [Ca²⁺]. The extent of facilitation correlated with the level of pre-activating [Ca²⁺] used. For each modeled condition a minimum of 1000 stochastic simulations were performed to compute the average response. ***p < 0.001 using the one-sided students’ t-test comparison to the control condition with no [Ca²⁺]_basal. The source data is provided as a ‘Source Data’ file.