A Schematic depiction of smFRET assay. Positions of FRET label pair (S95C/S171C) in Syx1 are indicated as yellow pentagrams. 6×His-tagged Syx1 bound to Munc18-1 was immobilized on coverslip coated with PEG/PEG-NTA-Co2+. Syx1 linker region is colored by black. 