The synaptotagmin 1 linker may function as an electrostatic zipper that opens for docking but closes for fusion pore opening

Synaptotagmin 1 (Syt1), 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 the single vesicle docking and content mixing assay 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 while 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. The EPR analysis showed Ca2+-induced line broadening reflecting a conformational change in the linker region. Thus, the results suggest that the electrostatically bipartite linker region might have some capacity to extend for docking and fold to facilitate pore opening.

Source: BJ Cell - September 4, 2013 Category: Biochemistry Authors: Y Lai, X Lou, Y Jho, T Yoon, Y Shin Tags: BJ Cell Source Type: research