Characterization of the complexin-SNARE quaternary complex. A. The fusion clamp model proposes that complexin can replace the C terminus of VAMP2 upon binding to the trans-SNARE complex (adapted from ref. 34). Positions 69, 76, 83, 86 and 89 are the spin-labeled sites of the soluble VAMP2. Positions 35 and 28 of complexin have also been shown in the model. Positions 42, 25 and 22, which are located at the N-terminal of complexin, have not been shown. B. The flow diagram of purification of the complexin-SNARE quaternary complex. C. SDS-PAGE analysis of the purified complexin-SNARE quaternary complex.