Fig. 3.
The secretory SNARE proteins from M. brevicollis form a highly stable, SDS-resistant complex. (A) Approximately stoichiometric amounts of SNAP-25, syntaxin 1, and synaptobrevin from R. norvegicus or from M. brevicollis were mixed and incubated for 3 h at RT. Without prior boiling, the secretory SNARE proteins from both species form ternary SDS-resistant complexes (tc) as indicated (37). (B) The core SNARE complex from M. brevicollis exhibits a hysteresis in the unfolding and refolding transitions similar to the one found for the rat complex (41). The core SNARE complex consisting of Syx1 (200-279), Syb (1-75), and SNAP-25 was purified by ion exchange and measured in PBS buffer, pH 7.4. Unfolding of the α-helical complex occurred at Tm ∼ 80 °C (black curve), whereas refolding was observable only at ≈50 °C (gray curve). The transitions were observed at 222 nm.