Journal
BIOPHYSICAL JOURNAL
Volume 118, Issue 3, Pages 643-656Publisher
CELL PRESS
DOI: 10.1016/j.bpj.2019.12.021
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Funding
- Human Frontier Science Program (HFSP) postdoctoral fellowship [LT000419/2015]
- Israeli National Postdoctoral Award for Advancing Women in Science
- L'Oreal UNESCO
- Nederlandse Organisatie voor Wetenschappelijk Onderzoek Vidi grant
- Welch Foundation [I-1304]
- National Institutes of Health [R35 NS097333]
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Synaptotagmin-1 (Syt1) is a calcium sensor protein that is critical for neurotransmission and is therefore extensively studied. Here, we use pairs of optically trapped beads coated with SNARE-free synthetic membranes to investigate Syt1-induced membrane remodeling. This activity is compared with that of Doc2b, which contains a conserved C(2)AB domain and induces membrane tethering and hemifusion in this cell-free model. We find that the soluble C(2)AB domain of Syt1 strongly affects the probability and strength of membrane-membrane interactions in a strictly Ca2+ - and protein-dependent manner. Single-membrane loading of Syt1 yielded the highest probability and force of membrane interactions, whereas in contrast, Doc2b was more effective after loading both membranes. A lipid-mixing assay with confocal imaging reveals that both Syt1 and Doc2b are able to induce hemifusion; however, significantly higher Syt1 concentrations are required. Consistently, both C(2)AB fragments cause a reduction in the membrane-bending modulus, as measured by a method based on atomic force microscopy. This lowering of the energy required for membrane deformation may contribute to Ca2+-induced fusion.
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