title: Dual roles of Munc18-1 rely on distinct binding modes of the central cavity with Stx1A and SNARE complex.
abstract: Sec1/Munc18 proteins play a fundamental role in multiple steps of intracellular membrane trafficking. Dual functions have been attributed to Munc18-1: it can act as a chaperone when it interacts with monomeric syntaxin 1A, and it can activate soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) for membrane fusion when it binds to SNARE complexes. Although both modes of binding involve the central cavity of Munc18-1, their precise molecular mechanisms of action are not fully understood. In this paper, we describe a novel Munc18-1 mutant in the central cavity that showed a reduced interaction with syntaxin 1A and impaired chaperone function, but still bound to assembled SNARE complexes and promoted liposome fusion and secretion in neuroendocrine cells. Soluble syntaxin 1A H3 domain partially blocks Munc18-1 activation of liposome fusion by occupying the Munc18-1 central cavity. Our findings lead us to propose a transition model between the two distinct binding modes by which Munc18 can control and assist in SNARE-complex assembly during neurotransmitter release.
authors: Department of Cell Biology, School of Medicine, Yale University, New Haven, CT 06520, USA.
authors: Lei
authors: L
authors: Shi
authors: Daniel
authors: D
authors: Kümmel
authors: Jeff
authors: J
authors: Coleman
authors: Thomas J
authors: TJ
authors: Melia
authors: Claudio G
authors: CG
authors: Giraudo
mesh_terms: D000818:Animals; D002151:Calorimetry; D002462:Cell Membrane / Q000378:metabolism; D006367:HeLa Cells; D019382:Human Growth Hormone / Q000378:metabolism; D006801:Humans; D008081:Liposomes / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D051938:Munc18 Proteins / Q000235:genetics / Q000378:metabolism*; D055099:Neuroendocrine Cells / Q000378:metabolism; D016716:PC12 Cells; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D021381:Protein Transport; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D050600:SNARE Proteins / Q000378:metabolism*; D050827:Syntaxin 1 / Q000378:metabolism*; D013816:Thermodynamics; D017186:Titrimetry
chemical_list: D008081:Liposomes; D018832:Molecular Chaperones; D051938:Munc18 Proteins; D011994:Recombinant Proteins; D050600:SNARE Proteins; C494213:Stx1a protein, rat; C497939:Stxbp1 protein, rat; D050827:Syntaxin 1; D019382:Human Growth Hormone