Secretory Vesicles Are Preferentially Targeted to Areas of Low Molecular SNARE Density

Abstract

Intercellular communication is commonly mediated by the regulated fusion, or exocytosis, of vesicles with the cell surface. SNARE (soluble N-ethymaleimide sensitive factor attachment protein receptor) proteins are the catalytic core of the secretory machinery, driving vesicle and plasma membrane merger. Plasma membrane SNAREs (tSNAREs) are proposed to reside in dense clusters containing many molecules, thus providing a concentrated reservoir to promote membrane fusion. However, biophysical experiments suggest that a small number of SNAREs are sufficient to drive a single fusion event. Here we show, using molecular imaging, that the majority of tSNARE molecules are spatially separated from secretory vesicles. Furthermore, the motilities of the individual tSNAREs are constrained in membrane micro-domains, maintaining a non-random molecular distribution and limiting the maximum number of molecules encountered by secretory vesicles. Together our results provide a new model for the molecular mechanism of regulated exocytosis and demonstrate the exquisite organization of the plasma membrane at the level of individual molecular machines.

Contact-induced clustering of syntaxin and munc18 docks secretory granules at the exocytosis site

“…Syntaxin was C-terminally labelled, resulting in EGFP being on the outside of the plasma membrane. Note that an N-terminal fusion where EGFP is adjacent to the Habc domain has been reported to be excluded from the docking site 68 . Munc18-EGFP rescues hormone secretion after siRNA-mediated knockdown of Munc18-1 and Munc18-2 in PC12 cells 18 .…”

Rapid Formation of a Supramolecular Polypeptide–DNA Hydrogel for In Situ Three‐Dimensional Multilayer Bioprinting

“…[12] Next, cell cultures of two types of cells (AtT-20 and HEK-293 cells) were monitored for aprolonged period of time,w hich showed that the cells maintained their high viability ( Figure S5), demonstrating that the hydrogel is mechanically strong enough to provide physical support for the encapsulated cells,n on-toxic to cells,a nd permeable for nutrients,which are desirable properties for the long-term use of cell cultures.…”

PI(4,5)P2-binding effector proteins for vesicle exocytosis

“…However, the strongest colocalization is with vesicles and PI(4,5)P 2 domains (30–50%) rather than with syntaxin-1 clusters. Additional live cell studies monitoring PI(4,5)P 2 , syntaxin-1 and vesicle exocytosis are needed to assess this especially since there are reports that secretory vesicles localize to sites of low SNARE density [84]. The exact function of syntaxin-1 clusters in vesicle exocytosis is currently unclear [85].…”