Formation of a yeast SNARE complex is accompanied by significant structural changes.

The evolutionarily conserved SNARE (SNAP receptor) proteins and their complexes are key players in the docking and fusion of secretory vesicles with their target membrane. Biophysical techniques were used to characterize structural and energetic properties of the cytoplasmic domains of the yeast SNAREs Snc1 and Sso1, of the SNAP-25-like domain of Sec9, and of the Sso1:Sec9 and Sso1:Sec9:Snc1 complexes. Individually, all three SNAREs are monomeric; Sso1 shows significant secondary structure while Snc1 and Sec9 are largely unstructured. Ternary SNARE complex formation (KD <50 nM) is accompanied by a more than two-fold increase in secondary structure. This binding induced structure, the large increase in thermal stability, and the self-association of the ternary complex represent conserved properties of SNAREs that are probably important in vesicle docking and fusion.