Exocytotic fusion pores are composed of both lipids and proteins
Chapman, Edwin R
Nature Structural and Molecular Biology
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Bao, H., Goldschen-Ohm, M., Jeggle, P., Chanda, B., Edwardson, M., & Chapman, E. R. (2015). Exocytotic fusion pores are composed of both lipids and proteins. Nature Structural and Molecular Biology, 23 67-73. https://doi.org/10.1038/nsmb.3141
During exocytosis, fusion pores form the first aqueous connection that allows escape of neurotransmitters and hormones from secretory vesicles. Although it is well established that SNARE proteins catalyze fusion, the structure and composition of fusion pores remain unknown. Here, we exploited the rigid framework and defined size of nanodiscs to interrogate the properties of reconstituted fusion pores, using the neurotransmitter glutamate as a content-mixing marker. Efficient Ca²⁺-stimulated bilayer fusion, and glutamate release, occurred with approximately two molecules of mouse synaptobrevin 2 reconstituted into ~6-nm nanodiscs. The transmembrane domains of SNARE proteins assumed distinct roles in lipid mixing versus content release and were exposed to polar solvent during fusion. Additionally, tryptophan substitutions at specific positions in these transmembrane domains decreased glutamate flux. Together, these findings indicate that the fusion pore is a hybrid structure composed of both lipids and proteins.
We thank Gerhard Wagner for providing the MSP∆1D1H4-H6 plasmid. This study was supported by a grant from the US National Institutes of Health (MH061876). H.B. is supported by a postdoctoral fellowship from Human Frontier Science Program. B.C. and M.P.G are supported by funding from the US National Institutes of Health (R01 GM084140). P.J. is supported by Kidney Research UK. J.M.E. is supported by the Biotechnology and Biological Sciences Research Council (BB/J018236/1) and Kidney Research UK. E.R.C. is supported as an Investigator of the Howard Hughes Medical Institute.
External DOI: https://doi.org/10.1038/nsmb.3141
This record's URL: https://www.repository.cam.ac.uk/handle/1810/252910