Differential interaction of tomosyn with syntaxin and SNAP25 depends on domains in the WD40 β-propeller core and determines its inhibitory activity.
Noa Bielopolski, Alice D Lam, Dana Bar-On, Markus Sauer, Edward L Stuenkel, Uri Ashery
Author Information
Noa Bielopolski: From the Department of Neurobiology, Life Sciences Faculty, and.
Alice D Lam: the Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan 48109, and.
Dana Bar-On: From the Department of Neurobiology, Life Sciences Faculty, and Sagol School of Neuroscience, Tel Aviv University, 69978 Tel Aviv, Israel.
Markus Sauer: the Department of Biotechnology and Biophysics, Julius Maximilians University Würzburg, Am Hubland, 97074 Würzburg, Germany.
Edward L Stuenkel: the Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan 48109, and.
Uri Ashery: From the Department of Neurobiology, Life Sciences Faculty, and Sagol School of Neuroscience, Tel Aviv University, 69978 Tel Aviv, Israel, uria@post.tau.ac.il.
Neuronal exocytosis depends on efficient formation of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes and is regulated by tomosyn, a SNARE-binding protein. To gain new information about tomosyn's activity, we characterized its mobility and organization on the plasma membrane (PM) in relation to other SNARE proteins and inhibition of exocytosis. By using direct stochastic optical reconstruction microscopy (dSTORM), we found tomosyn to be organized in small clusters adjacent to syntaxin clusters. In addition, we show that tomosyn is present in both syntaxin-tomosyn complexes and syntaxin-SNAP25-tomosyn complexes. Tomosyn mutants that lack residues 537-578 or 897-917 from its β-propeller core diffused faster on the PM and exhibited reduced binding to SNAP25, suggesting that these mutants shift the equilibrium between tomosyn-syntaxin-SNAP25 complexes on the PM to tomosyn-syntaxin complexes. As these deletion mutants impose less inhibition on exocytosis, we suggest that tomosyn inhibition is mediated via tomosyn-syntaxin-SNAP25 complexes and not tomosyn-syntaxin complexes. These findings characterize, for the first time, tomosyn's dynamics at the PM and its relation to its inhibition of exocytosis.
