Single-vesicle architecture of synaptobrevin2 in astrocytes

• DOI: 10.1038/ncomms4780
• Publication Date: 2014-05-07T14:23:11Z
• Authors: Priyanka Singh; Jernej Jorgačevski; Marko Kreft; Vladimir Grubišić; Randy F. Stout; Maja Potokar; Vladimir Parpura; Robert Zorec
• Keywords: 0303 health sciences; Photobleaching; Vesicle-Associated Membrane Protein 2; Green Fluorescent Proteins; Brain; Membrane Fusion; Exocytosis; Rats; 03 medical and health sciences; Adenosine Triphosphate; Microscopy, Fluorescence; Astrocytes; Animals; Female; SNARE Proteins; Transport Vesicles; Cells, Cultured

Exocytic transmitter release is regulated by the SNARE complex, which contains a vesicular protein, synaptobrevin2 (Sb2). However, Sb2 vesicular arrangement is unclear. Here we use super-resolution fluorescence microscopy to study the prevalence and distribution of endogenous and exogenous Sb2 in single vesicles of astrocytes, the most abundant glial cells in the brain. We tag Sb2 protein at C- and N termini with a pair of fluorophores, which allows us to determine the Sb2 length and geometry. To estimate total number of Sb2 proteins per vesicle and the quantity necessary for the formation of fusion pores, we treat cells with ATP to stimulate Ca2+-dependent exocytosis, increase intracellular alkalinity to enhance the fluorescence presentation of yellow-shifted pHluorin (YpH), appended to the vesicle lumen domain of Sb2, and perform photobleaching of YpH fluorophores. Fluorescence intensity analysis reveals that the total number of endogenous Sb2 units or molecules per vesicle is ≤25.