Three-helical SNARE proteins offer binary immobilization system. (A) Schematic showing fusions of brevin to the N-terminus (B-S) or C-terminus (S-B) of SNAP25. These two proteins are designed to bind syntaxin. (B) Coomassie-stained gel showing bacterially-expressed three-helical SNARE proteins. (C) Coomassie-stained gel showing that the three-helical SNARE proteins can bind to syntaxin but not control beads. (D) Pull-down showing complexin only binds syntaxin beads with B-S or S-B immobilized. Coomassie-stained gel.