The synaptotagmin C2B domain calcium-binding loops modulate the rate of fusion pore expansion (original) (raw)
2018, Molecular biology of the cell
In chromaffin cells, the kinetics of fusion pore expansion vary depending on which synaptotagmin isoform (Syt-1 or Syt-7) drives release. Our recent studies have shown that fusion pores of granules harboring Syt-1 expand more rapidly than those harboring Syt-7. Here, we sought to define the structural specificity of synaptotagmin action at the fusion pore by manipulating the Ca-binding C2B module. We generated a chimeric Syt-1 in which its C2B Ca-binding loops had been exchanged for those of Syt-7. Fusion pores of granules harboring a Syt-1 C2B chimera with all three Ca-binding loops of Syt-7 (Syt-1:7C2B) exhibited slower rates of fusion pore expansion and neuropeptide cargo release relative to WT Syt-1. After fusion, this chimera also dispersed more slowly from fusion sites than WT protein. We speculate that the Syt-1:7 C2Band WT Syt-1 are likely to differ in their interactions with Caand membranes. Subsequentanddata demonstrated that the chimera exhibits a higher affinity for phos...
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