title: Chaperoning of closed syntaxin-3 through Lys46 and Glu59 in domain 1 of Munc18 proteins is indispensable for mast cell exocytosis.
abstract: Understanding how Munc18 proteins govern exocytosis is crucial because mutations of this protein cause severe secretion deficits in neuronal and immune cells. Munc18-2 has indispensable roles in the degranulation of mast cell, partly by binding and chaperoning a subset of syntaxin isoforms. However, the key syntaxin that, crucially, participates in the degranulation – whose levels and intracellular localization are regulated by Munc18-2 – remains unknown. Here, we demonstrate that double knockdown of Munc18-1 and Munc-2 in mast cells results in greatly reduced degranulation accompanied with strikingly compromised expression levels and localization of syntaxin-3. This phenotype is fully rescued by wild-type Munc18 proteins but not by the K46E, E59K and K46E/E59K mutants of Munc-18 domain 1, each of which exhibits completely abolished binding to 'closed' syntaxin-3. Furthermore, knockdown of syntaxin-3 strongly impairs degranulation. Collectively, our data argue that residues Lys46 and Glu59 of Munc18 proteins are indispensable for mediating the interaction between Munc18 and closed syntaxin-3, which is essential for degranulation by chaperoning syntaxin-3. Our results also indicate that the functional contribution of these residues differs between immune cell degranulation and neuronal secretion.
authors: Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada.
authors: Na-Ryum
authors: NR
authors: Bin
authors: Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada.
authors: Chang Hun
authors: CH
authors: Jung
authors: Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada.
authors: Byungjin
authors: B
authors: Kim
authors: Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada.
authors: Prashanth
authors: P
authors: Chandrasegram
authors: Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada Department of Surgery, University of Toronto, Toronto, ON M5S 1A8, Canada.
authors: Ekaterina
authors: E
authors: Turlova
authors: Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada Department of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada.
authors: Dan
authors: D
authors: Zhu
authors: Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada Department of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada.
authors: Herbert Y
authors: HY
authors: Gaisano
authors: Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada Department of Surgery, University of Toronto, Toronto, ON M5S 1A8, Canada.
authors: Hong-Shuo
authors: HS
authors: Sun
authors: Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada ssugita@uhnres.utoronto.ca.
authors: Shuzo
authors: S
authors: Sugita
mesh_terms: D000818:Animals; D005089:Exocytosis; D006801:Humans; D008407:Mast Cells / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D051938:Munc18 Proteins / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics*; D050765:Qa-SNARE Proteins / Q000378:metabolism*; D051381:Rats
chemical_list: D018832:Molecular Chaperones; D051938:Munc18 Proteins; D050765:Qa-SNARE Proteins
keywords: Exocytosis; Mast cell; Membrane trafficking; Munc18; SNARE; Secretion