Fig. 8. The syntaxin-1 open mutant partially bypasses the requirement of Munc13-1 but not Munc18-1 for liposome fusion.

a–d Lipid mixing (a, c) between V- and T-liposomes (containing syntaxin-1 (Syx) WT or LE open mutant) was monitored from the fluorescence de-quenching of Marina Blue lipids and content mixing (b, d) was monitored from the increase in the fluorescence signal of Cy5-streptavidin trapped in the V-liposomes caused by FRET with PhycoE-biotin trapped in the T-liposomes upon liposome fusion. In a, b, assays were performed in the presence of NSF, αSNAP, the synaptotagmin-1 C₂AB fragment and the Munc13-1 C₁C₂BMUNC₂C fragment with (green and black traces) or without (red and blue traces) Munc18-1. In c, d, assays were performed in the presence of NSF, α-SNAP, the synaptotagmin-1 C₂AB fragment and Munc18-1, without the Munc13-1 C₁C₂BMUNC₂C fragment. Experiments were started in the presence of 100 µM EGTA and 5 µM streptavidin, and Ca²⁺ (600 µM) was added at 300 s.