A Ensemble FRET assay showing the different effects of the Munc18-1 P335A mutation and the Syx1 LEAA mutation in the transition from the Munc18-1/Syx1 complex to the SNARE complex with and without the MUN domain. FRET signal between BODIPY FL-labeled Syb2 (donor) and TMR-labeled SN25 (acceptor) was monitored.