title: The N- and C-terminal domains of tomosyn play distinct roles in soluble N-ethylmaleimide-sensitive factor attachment protein receptor binding and fusion regulation.
abstract: Tomosyn negatively regulates SNARE-dependent exocytic pathways including insulin secretion, GLUT4 exocytosis, and neurotransmitter release. The molecular mechanism of tomosyn, however, has not been fully elucidated. Here, we reconstituted SNARE-dependent fusion reactions in vitro to recapitulate the tomosyn-regulated exocytic pathways. We then expressed and purified active full-length tomosyn and examined how it regulates the reconstituted SNARE-dependent fusion reactions. Using these defined fusion assays, we demonstrated that tomosyn negatively regulates SNARE-mediated membrane fusion by inhibiting the assembly of the ternary SNARE complex. Tomosyn recognizes the t-SNARE complex and prevents its pairing with the v-SNARE, therefore arresting the fusion reaction at a pre-docking stage. The inhibitory function of tomosyn is mediated by its C-terminal domain (CTD) that contains an R-SNARE-like motif, confirming previous studies carried out using truncated tomosyn fragments. Interestingly, the N-terminal domain (NTD) of tomosyn is critical (but not sufficient) to the binding of tomosyn to the syntaxin monomer, indicating that full-length tomosyn possesses unique features not found in the widely studied CTD fragment. Finally, we showed that the inhibitory function of tomosyn is dominant over the stimulatory activity of the Sec1/Munc18 protein in fusion. We suggest that tomosyn uses its CTD to arrest SNARE-dependent fusion reactions, whereas its NTD is required for the recruitment of tomosyn to vesicle fusion sites through syntaxin interaction.
authors: From the Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309.
authors: Haijia
authors: H
authors: Yu
authors: From the Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309.
authors: Shailendra S
authors: SS
authors: Rathore
authors: From the Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309.
authors: Daniel R
authors: DR
authors: Gulbranson
authors: From the Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309 jingshi.shen@colorado.edu.
authors: Jingshi
authors: J
authors: Shen
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D005033:Ethylmaleimide / Q000737:chemistry; D005089:Exocytosis / Q000235:genetics*; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D008561:Membrane Fusion / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism*; D016716:PC12 Cells; D060066:Protein Interaction Maps / Q000235:genetics; D017434:Protein Structure, Tertiary; D050765:Qa-SNARE Proteins / Q000378:metabolism; D050683:R-SNARE Proteins / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D050600:SNARE Proteins / Q000235:genetics; D009435:Synaptic Transmission / Q000235:genetics
chemical_list: D051275:Glucose Transporter Type 4; D009419:Nerve Tissue Proteins; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; C495692:SLC2A4 protein, human; D050600:SNARE Proteins; C484769:Stxbp5 protein, rat; D005033:Ethylmaleimide
keywords: Exocytosis; Membrane; Membrane Bilayer; Membrane Fusion; Membrane Trafficking; Vesicles