期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2014
卷号：111
期号：38
页码：13828-13833
DOI：10.1073/pnas.1408254111
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceEvery vesicle fusion reaction is driven by soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins that zipper into tight complexes between membranes. Members of the Sec1/Munc18 (SM) family tightly regulate this process through interactions with a member of the syntaxin SNARE subfamily. However, seemingly different interaction modes have been found for different SM proteins and syntaxins. Here we show that the ER-Golgi SM protein Sly1 interacts not only with the N-peptide of the syntaxin Sed5, as previously thought, but also with its remainder. This corroborates the idea that SM proteins and syntaxins generally make use of two spatially separated binding sites. Remarkably, binding of Sly1 relaxes the autoinhibitory closed conformation of Sed5 and thereby accelerates SNARE complex formation. Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) and Sec1/Munc18 (SM) proteins constitute the core of an ancient vesicle fusion machine that diversified into distinct sets that now function in different trafficking steps in eukaryotic cells. Deciphering their precise mode of action has proved challenging. SM proteins are thought to act primarily through one type of SNARE protein, the syntaxins. Despite high structural similarity, however, contrasting binding modes have been found for different SM proteins and syntaxins. Whereas the secretory SM protein Munc18 binds to the "closed conformation" of syntaxin 1, the ER-Golgi SM protein Sly1 interacts only with the N-peptide of Sed5. Recent findings, however, indicate that SM proteins might interact simultaneously with both syntaxin regions. In search for a common mechanism, we now reinvestigated the Sly1/Sed5 interaction. We found that individual Sed5 adopts a tight closed conformation. Sly1 binds to both the closed conformation and the N-peptide of Sed5, suggesting that this is the original binding mode of SM proteins and syntaxins. In contrast to Munc18, however, Sly1 facilitates SNARE complex formation by loosening the closed conformation of Sed5.
