Schematic representation of the protein constructs used in this study.

In vivo full-length Sx consists of an N-peptide preceding an N-terminal α-helical bundle (the Habc domain), a SNARE motif (the H3 helix) and a C-terminal transmembrane region. We used soluble Sx1 and Sx4 constructs lacking the transmembrane domain for experiments reported here. ΔN indicates Sx constructs lacking the N-peptide. Munc18 and SNAP25 and VAMP2 constructs used in these experiments are also shown. The positions of engineered fusion tags and protease cleavage sites are as indicated.