title: Differential Effects of Munc18s on Multiple Degranulation-Relevant Trans-SNARE Complexes.
abstract: Mast cell exocytosis, which includes compound degranulation and vesicle-associated piecemeal degranulation, requires multiple Q- and R- SNAREs. It is not clear how these SNAREs pair to form functional trans-SNARE complexes and how these trans-SNARE complexes are selectively regulated for fusion. Here we undertake a comprehensive examination of the capacity of two Q-SNARE subcomplexes (syntaxin3/SNAP-23 and syntaxin4/SNAP-23) to form fusogenic trans-SNARE complexes with each of the four granule-borne R-SNAREs (VAMP2, 3, 7, 8). We report the identification of at least six distinct trans-SNARE complexes under enhanced tethering conditions: i) VAMP2/syntaxin3/SNAP-23, ii) VAMP2/syntaxin4/SNAP-23, iii) VAMP3/syntaxin3/SNAP-23, iv) VAMP3/syntaxin4/SNAP-23, v) VAMP8/syntaxin3/SNAP-23, and vi) VAMP8/syntaxin4/SNAP-23. We show for the first time that Munc18a operates synergistically with SNAP-23-based non-neuronal SNARE complexes (i to iv) in lipid mixing, in contrast to Munc18b and c, which exhibit no positive effect on any SNARE combination tested. Pre-incubation with Munc18a renders the SNARE-dependent fusion reactions insensitive to the otherwise inhibitory R-SNARE cytoplasmic domains, suggesting a protective role of Munc18a for its cognate SNAREs. Our findings substantiate the recently discovered but unexpected requirement for Munc18a in mast cell exocytosis, and implicate post-translational modifications in Munc18b/c activation.
authors.affiliation: Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, Mississippi, United States of America.
authors.forename: Hao
authors.initials: H
authors.lastname: Xu
authors.affiliation: Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, Mississippi, United States of America.
authors.forename: Matthew Grant
authors.initials: MG
authors.lastname: Arnold
authors.affiliation: Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, Mississippi, United States of America.
authors.forename: Sushmitha Vijay
authors.initials: SV
authors.lastname: Kumar
mesh_terms: D000818:Animals; D015550:Cell Degranulation / Q000502:physiology*; D006801:Humans; D051938:Munc18 Proteins / Q000502:physiology*; D050600:SNARE Proteins / Q000502:physiology*
chemical_list: D051938:Munc18 Proteins; D050600:SNARE Proteins