Vesicle motion and fusion are altered in chromaffin cells with increased SNARE cluster dynamics.
Traffic. 2009 Feb; 10(2):172-85
I found this paper interesting because of the measurement of the dynamics of SNARE-clusters and the implications for vesicle fusion probability.
Clusters of GFP-linked SNAP-25 in chromaffin cells were visualized under TIRF microscopy and it was found that a deletion of the last C-terminal amino acids led to more dynamic clusters with increased mobility. This mutation corresponds to the cleavage of SNAP-25 by Botulinum Toxin A (the main constituent of BOTOX). Increasing the intracellular calcium concentration stabilized the mutant clusters, which correlates with the observation by several labs that the effect of Botulinum Toxin A can be partly overcome by calcium. Thus, mobility of SNARE-clusters might be important for vesicle fusion, and the paper shows how this mobility can be measured simultaneously with vesicle fusion. A more puzzling result is that the mutant SNAP-25 clusters were also more mobile in the Z-axis (perpendicular to the plasma membrane) and here displayed movements far exceeding the length of the SNAREpin.
Soerensen J: F1000Prime Recommendation of [López I et al., Traffic 2009, 10(2):172-85]. In F1000Prime, 21 Jan 2009; DOI: 10.3410/f.1146942.604040. F1000Prime.com/1146942#eval604040
F1000Prime Recommendations, Dissents and Comments for [López I et al., Traffic 2009, 10(2):172-85]. In F1000Prime, 08 Dec 2013; F1000Prime.com/1146942
Neuron. 2001 Aug 30; 31(4):581-91
Nat Commun. 2011; 2:491
Sørensen JB. Pflugers Arch. 2004 Jul; 448(4):347-62
The expression of SNAP-25 fused to green fluorescent protein (GFP) has been instrumental in demonstrating SNARE role in exocytosis. The wild-type GFP-SNAP-25 and a Delta9 form, product of botulinum neurotoxin A activity, the main ingredient in the BOTOX preparation, were employed here to study SNARE implication in vesicle mobility and fusion in cultured bovine chromaffin cells, a neuroendocrine exocytotic model. Using total internal reflection fluorescent microscopy, we have identified membrane microdomains of 500-600 nm diameter that contain both SNAP-25 and syntaxin-1 and associate with synaptobrevin-2. Interestingly, while the SNAP-25 Delta9 formed similar clusters, they displayed increased mobility both laterally and in the axis perpendicular to the plasmalemma, and this correlates with the enhanced dynamics of associated chromaffin granules. SNARE cluster-enhanced motion is reversed by elevation of the intracellular calcium level. Furthermore, single vesicle fusion was unlikely in the highly mobile vesicles present in the cells expressing SNAP-25 Delta9, which, in addition, displayed in average slower fusion kinetics. Consequently, SNARE cluster dynamics is a new aspect to consider when determining the factors contributing to the mobility of the vesicles in close vicinity to the plasma membrane and also the probability of exocytosis of this granule population.
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