scholarly journals The Synaptotagmin-1 C2B Domain Is a Key Regulator in the Stabilization of the Fusion Pore

2020 ◽  
Vol 16 (12) ◽  
pp. 7840-7851
Author(s):  
Marcelo Caparotta ◽  
Claudia N. Tomes ◽  
Luis S. Mayorga ◽  
Diego Masone
Keyword(s):  
Fusion Pore ◽  
Synaptotagmin 1

scholarly journals The neuronal calcium sensor Synaptotagmin-1 and SNARE proteins cooperate to dilate fusion pores

2019 ◽  
Author(s):  
Zhenyong Wu ◽  
Nadiv Dharan ◽  
Sathish Thiyagarajan ◽  
Ben O’Shaughnessy ◽  
Erdem Karatekin
Keyword(s):  
Membrane Fusion ◽  
Snare Complex ◽  
Snare Proteins ◽  
Fusion Pore ◽  
Calcium Sensor ◽  
Fusion Reactions ◽  
Synaptotagmin 1 ◽  
Pore Opening ◽  
Pore Dilation ◽  
Fusion Pores

ABSTRACTAll membrane fusion reactions proceed through an initial fusion pore, including calcium-triggered vesicular release of neurotransmitters and hormones. Expansion of this small pore to release cargo molecules is energetically costly and regulated by cells, but the mechanisms are poorly understood. Here we show that the neuronal/exocytic calcium sensor Synaptotagmin-1 (Syt1) promotes expansion of fusion pores induced by SNARE proteins, beyond its established role in coupling calcium influx to fusion pore opening. Our results suggest that fusion pore dilation by Syt1 requires interactions with SNAREs, PI(4,5)P2, and calcium. Pore opening was abolished by a mutation of the tandem C2 domain (C2AB) hydrophobic loops of Syt1, suggesting that their calcium-induced insertion into the membrane is required for pore opening. We propose that loop insertion is also required for pore expansion, but through a distinct mechanism. Mathematical modelling suggests that membrane insertion re-orients the C2 domains bound to the SNARE complex, rotating the SNARE complex so as to exert force on the membranes in a mechanical lever action that increases the intermembrane distance. The increased membrane separation provokes pore dilation to offset a bending energy penalty. We conclude that Syt1 assumes a critical role in calcium-dependent fusion pore dilation during neurotransmitter and hormone release.SIGNIFICANCE STATEMENTMembrane fusion is a fundamental biological process, required for development, infection by enveloped viruses, fertilization, intracellular trafficking, and calcium-triggered release of neurotransmitters and hormones when cargo-laden vesicles fuse with the plasma membrane. All membrane fusion reactions proceed through an initial, nanometer-sized fusion pore which can flicker open-closed multiple times before expanding or resealing. Pore expansion is required for efficient cargo release, but underlying mechanisms are poorly understood. Using a combination of single-pore measurements and quantitative modeling, we suggest that a complex between the neuronal calcium sensor Synaptotagmin-1 and the SNARE proteins together act as a calcium-sensitive mechanical lever to force the membranes apart and enlarge the pore.

scholarly journals Fusion Pore Dilation by Synaptotagmin-1

2019 ◽  
Vol 116 (3) ◽  
pp. 526a
Author(s):  
Zhenyong Wu ◽  
Nadiv Dharan ◽  
Sathish Thiyagarajan ◽  
Ben O'Shaughnessy ◽  
Erdem Karatekin
Keyword(s):  
Fusion Pore ◽  
Synaptotagmin 1 ◽  
Pore Dilation

scholarly journals Fusion pore formation and expansion induced by Ca2+and synaptotagmin 1

2013 ◽  
Vol 110 (4) ◽  
pp. 1333-1338 ◽  
Author(s):  
Ying Lai ◽  
Jiajie Diao ◽  
Yanxin Liu ◽  
Yuji Ishitsuka ◽  
Zengliu Su ◽  
...  
Keyword(s):  
Pore Formation ◽  
Fusion Pore ◽  
Synaptotagmin 1

scholarly journals Molecular origins of synaptotagmin 1 activities on vesicle docking and fusion pore opening

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
Ying Lai ◽  
Xiaochu Lou ◽  
Jiajie Diao ◽  
Yeon-Kyun Shin
Keyword(s):  
Fusion Pore ◽  
Vesicle Docking ◽  
Synaptotagmin 1 ◽  
Pore Opening

scholarly journals Neuromodulator release in neurons requires two functionally redundant calcium sensors

2021 ◽  
Vol 118 (18) ◽  
pp. e2012137118
Author(s):  
Rhodé van Westen ◽  
Josse Poppinga ◽  
Rocío Díez Arazola ◽  
Ruud F. Toonen ◽  
Matthijs Verhage
Keyword(s):  
Neurotrophic Factors ◽  
Hippocampal Neurons ◽  
Fusion Pore ◽  
Dependent Manner ◽  
Wild Type ◽  
Unique Role ◽  
Brain Functions ◽  
Calcium Sensors ◽  
Synaptotagmin 1 ◽  
Rate Limiting

Neuropeptides and neurotrophic factors secreted from dense core vesicles (DCVs) control many brain functions, but the calcium sensors that trigger their secretion remain unknown. Here, we show that in mouse hippocampal neurons, DCV fusion is strongly and equally reduced in synaptotagmin-1 (Syt1)- or Syt7-deficient neurons, but combined Syt1/Syt7 deficiency did not reduce fusion further. Cross-rescue, expression of Syt1 in Syt7-deficient neurons, or vice versa, completely restored fusion. Hence, both sensors are rate limiting, operating in a single pathway. Overexpression of either sensor in wild-type neurons confirmed this and increased fusion. Syt1 traveled with DCVs and was present on fusing DCVs, but Syt7 supported fusion largely from other locations. Finally, the duration of single DCV fusion events was reduced in Syt1-deficient but not Syt7-deficient neurons. In conclusion, two functionally redundant calcium sensors drive neuromodulator secretion in an expression-dependent manner. In addition, Syt1 has a unique role in regulating fusion pore duration.

scholarly journals Conserved arginine residues in synaptotagmin 1 regulate fusion pore expansion through membrane contact

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Sarah B. Nyenhuis ◽  
Nakul Karandikar ◽  
Volker Kiessling ◽  
Alex J. B. Kreutzberger ◽  
Anusa Thapa ◽  
...  
Keyword(s):  
Binding Sites ◽  
Membrane Surface ◽  
Fusion Pore ◽  
Fusion Event ◽  
Fusion Probability ◽  
Arginine Residues ◽  
Synaptotagmin 1 ◽  
Membrane Contact ◽  
Curved Membrane ◽  
Pore Expansion

AbstractSynaptotagmin 1 is a vesicle-anchored membrane protein that functions as the Ca2+ sensor for synchronous neurotransmitter release. In this work, an arginine containing region in the second C2 domain of synaptotagmin 1 (C2B) is shown to control the expansion of the fusion pore and thereby the concentration of neurotransmitter released. This arginine apex, which is opposite the Ca2+ binding sites, interacts with membranes or membrane reconstituted SNAREs; however, only the membrane interactions occur under the conditions in which fusion takes place. Other regions of C2B influence the fusion probability and kinetics but do not control the expansion of the fusion pore. These data indicate that the C2B domain has at least two distinct molecular roles in the fusion event, and the data are consistent with a model where the arginine apex of C2B positions the domain at the curved membrane surface of the expanding fusion pore.

scholarly journals The neuronal calcium sensor Synaptotagmin-1 and SNARE proteins cooperate to dilate fusion pores

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Zhenyong Wu ◽  
Nadiv Dharan ◽  
Zachary A McDargh ◽  
Sathish Thiyagarajan ◽  
Ben O'Shaughnessy ◽  
...  
Keyword(s):  
Snare Complex ◽  
Snare Proteins ◽  
Fusion Pore ◽  
C2 Domain ◽  
Calcium Sensor ◽  
Fusion Reactions ◽  
Small Pore ◽  
Synaptotagmin 1 ◽  
Pore Dilation ◽  
Fusion Pores

All membrane fusion reactions proceed through an initial fusion pore, including calcium-triggered release of neurotransmitters and hormones. Expansion of this small pore to release cargo is energetically costly and regulated by cells, but the mechanisms are poorly understood. Here we show that the neuronal/exocytic calcium sensor Synaptotagmin-1 (Syt1) promotes expansion of fusion pores induced by SNARE proteins. Pore dilation relied on calcium-induced insertion of the tandem C2 domain hydrophobic loops of Syt1 into the membrane, previously shown to reorient the C2 domain. Mathematical modelling suggests that C2B reorientation rotates a bound SNARE complex so that it exerts force on the membranes in a mechanical lever action that increases the height of the fusion pore, provoking pore dilation to offset the bending energy penalty. We conclude that Syt1 exerts novel non-local calcium-dependent mechanical forces on fusion pores that dilate pores and assist neurotransmitter and hormone release.

scholarly journals Distinct fusion properties of synaptotagmin-1 and synaptotagmin-7 bearing dense core granules

2014 ◽  
Vol 25 (16) ◽  
pp. 2416-2427 ◽  
Author(s):  
Tejeshwar C. Rao ◽  
Daniel R. Passmore ◽  
Andrew R. Peleman ◽  
Madhurima Das ◽  
Edwin R. Chapman ◽  
...  
Keyword(s):  
Chromaffin Cells ◽  
Secretory Granules ◽  
Fusion Pore ◽  
Cargo Proteins ◽  
Granule Membrane ◽  
Synaptotagmin 1 ◽  
Physiological Homeostasis ◽  
Dense Core Granules ◽  
Adrenal Chromaffin ◽  
Granule Membrane Proteins

Adrenal chromaffin cells release hormones and neuropeptides that are essential for physiological homeostasis. During this process, secretory granules fuse with the plasma membrane and deliver their cargo to the extracellular space. It was once believed that fusion was the final regulated step in exocytosis, resulting in uniform and total release of granule cargo. Recent evidence argues for nonuniform outcomes after fusion, in which cargo is released with variable kinetics and selectivity. The goal of this study was to identify factors that contribute to the different outcomes, with a focus on the Ca2+-sensing synaptotagmin (Syt) proteins. Two Syt isoforms are expressed in chromaffin cells: Syt-1 and Syt-7. We find that overexpressed and endogenous Syt isoforms are usually sorted to separate secretory granules and are differentially activated by depolarizing stimuli. In addition, overexpressed Syt-1 and Syt-7 impose distinct effects on fusion pore expansion and granule cargo release. Syt-7 pores usually fail to expand (or reseal), slowing the dispersal of lumenal cargo proteins and granule membrane proteins. On the other hand, Syt-1 diffuses from fusion sites and promotes the release of lumenal cargo proteins. These findings suggest one way in which chromaffin cells may regulate cargo release is via differential activation of synaptotagmin isoforms.

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