title: The synaptotagmin 1 linker may function as an electrostatic zipper that opens for docking but closes for fusion pore opening.
abstract: Syt1 (synaptotagmin 1), a major Ca2+ sensor for fast neurotransmitter release, contains tandem Ca2+-binding C2 domains (C2AB), a single transmembrane α-helix and a highly charged 60-residue-long linker in between. Using single-vesicle-docking and content-mixing assays we found that the linker region of Syt1 is essential for its two signature functions: Ca2+-independent vesicle docking and Ca2+-dependent fusion pore opening. The linker contains the basic-amino-acid-rich N-terminal region and the acidic-amino-acid-rich C-terminal region. When the charge segregation was disrupted, fusion pore opening was slowed, whereas docking was unchanged. Intramolecular disulfide cross-linking between N- and C-terminal regions of the linker or deletion of 40 residues from the linker reduced docking while enhancing pore opening, although the changes were subtle. EPR analysis showed Ca2+-induced line broadening reflecting a conformational change in the linker region. Thus the results of the present study suggest that the electrostatically bipartite linker region may extend for docking and fold to facilitate pore opening.
authors.affiliation: *Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011, U.S.A.
authors.forename: Ying
authors.initials: Y
authors.lastname: Lai
authors.forename: Xiaochu
authors.initials: X
authors.lastname: Lou
authors.forename: Yongseok
authors.initials: Y
authors.lastname: Jho
authors.forename: Tae-Young
authors.initials: TY
authors.lastname: Yoon
authors.forename: Yeon-Kyun
authors.initials: YK
authors.lastname: Shin
mesh_terms: D000818:Animals; D002118:Calcium / Q000737:chemistry; D002413:Cations, Divalent; D003432:Cross-Linking Reagents / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry; D008055:Lipids / Q000737:chemistry; D008561:Membrane Fusion; D008567:Membranes, Artificial; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D051381:Rats; D050600:SNARE Proteins / Q000737:chemistry; D055672:Static Electricity; D013572:Synaptic Vesicles / Q000737:chemistry; D050863:Synaptotagmin I / Q000737:chemistry* / Q000235:genetics
chemical_list: D002413:Cations, Divalent; D003432:Cross-Linking Reagents; D004220:Disulfides; D008055:Lipids; D008567:Membranes, Artificial; D050600:SNARE Proteins; D050863:Synaptotagmin I; D002118:Calcium