Figure 1.

The cartoons are modeled after the figures in Kiessling et al. (15). Membrane-bound syntaxin1A was labeled with Alexa Fluor 546 at amino acid 192, located on the N-terminus of its SNARE motif (thick red line). The N-terminal Habc domain of syntaxin is not shown, although it was present in most of the experiments. The two SNARE motifs of SNAP25 are depicted as two parallel blue lines without showing the linker region. Membrane-bound synaptobrevin 2 (black line) was used to model the cis SNARE complex (D). Synaptobrevin 2 without the transmembrane domain was used to model the trans-SNARE complex without (C) and with (E) the C2AB domain of synaptotagmin1. The possibility that C2AB confers stress to the bilayer when the SNAREs are in a trans configuration is indicated in (E). The indicated distances correspond to the distances of the fluorophore from the supported bilayer. They are approximate and depend on experimental conditions including lipids in the supported bilayer. The 2-nm distance in (A) is from (14). The distances in (B–E) were taken from (15). The distance for the acceptor complex in (B) was determined with full-length syntaxin1A and dodecylated (membrane-bound) SNAP25. The distances in (C–E) were obtained with cysteine-free SNAP25 (without acyl fatty acids). Similar results were obtained for the cis-SNARE complex depicted in (D) when the complex was reconstituted with full length syntaxin1A, dodecylated (membrane-bound) SNAP25, and full-length (membrane-bound) synaptobrevin 2 (V. Kiessling, personal communication). To see this figure in color, go online.