Lee, Sanghwa Shin, Jonghyeok Jung, Younghun Son, Heyjin Shin, Jaeil Jeong, Cherlhyun Kweon, Dae-Hyuk Shin, Yeon-Kyun 2024-01-19T17:03:10Z 2024-01-19T17:03:10Z 2021-09-05 2020-07 https://pubs.kist.re.kr/handle/201004/118381 In neuronal exocytosis, SNARE assembly into a stable four-helix bundle drives membrane fusion. Previous studies have revealed that the SM protein Munc18-1 plays a critical role for precise SNARE assembly with the help of Munc13-1, but the underlying mechanism remains unclear. Here, we used single-molecule FRET assays with a nanodisc membrane reconstitution system to investigate the conformational dynamics of SNARE/Munc18-1 complexes in multiple intermediate steps towards the SNARE complex. We found that single Munc18-1 proteins induce the closed conformation of syntaxin-1 not only in the free syntaxin-1 but also in the t-SNARE (syntaxin-1/SNAP-25) complex. These results implicate that Munc18-1 may act as a gatekeeper for both binary and ternary SNARE complex formation by locking the syntaxin-1 in a cleft of Munc18-1. Furthermore, the kinetic analysis of the opening/closing transition reveals that the closed syntaxin-1 in the syntaxin-1/SNAP-25/Munc18-1 complex is less stable than that in the closed syntaxin-1/Munc18-1 complex, which is manifested by the infrequent closing transition, indicating that the conformational equilibrium of the ternary complex is biased toward the open conformation of syntaxin-1 compared with the binary complex. English Nature Publishing Group Munc18-1 induces conformational changes of syntaxin-1 in multiple intermediates for SNARE assembly Article 10.1038/s41598-020-68476-3 1 Scientific Reports, v.10, no.1 Scientific Reports 10 1 N scie scopus 000550028900004 2-s2.0-85088018438 Multidisciplinary Sciences Science & Technology - Other Topics Article MEMBRANE-FUSION COMPLEX EXOCYTOSIS BINDS SNARE Munc18-1 syntaxin-1 single molecule FRET