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Mehta N, Mondal S, Watson ET, Cui Q, Chapman ER. The juxtamembrane linker of synaptotagmin 1 regulates Ca 2+ binding via liquid-liquid phase separation. Nat Commun 2024; 15:262. [PMID: 38177243 PMCID: PMC10766989 DOI: 10.1038/s41467-023-44414-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2023] [Accepted: 12/12/2023] [Indexed: 01/06/2024] Open
Abstract
Synaptotagmin (syt) 1, a Ca2+ sensor for synaptic vesicle exocytosis, functions in vivo as a multimer. Syt1 senses Ca2+ via tandem C2-domains that are connected to a single transmembrane domain via a juxtamembrane linker. Here, we show that this linker segment harbors a lysine-rich, intrinsically disordered region that is necessary and sufficient to mediate liquid-liquid phase separation (LLPS). Interestingly, condensate formation negatively regulates the Ca2+-sensitivity of syt1. Moreover, Ca2+ and anionic phospholipids facilitate the observed phase separation, and increases in [Ca2+]i promote the fusion of syt1 droplets in living cells. Together, these observations suggest a condensate-mediated feedback loop that serves to fine-tune the ability of syt1 to trigger release, via alterations in Ca2+ binding activity and potentially through the impact of LLPS on membrane curvature during fusion reactions. In summary, the juxtamembrane linker of syt1 emerges as a regulator of syt1 function by driving self-association via LLPS.
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Affiliation(s)
- Nikunj Mehta
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | - Sayantan Mondal
- Department of Chemistry, Boston University, Boston, MA, 02215, USA
| | - Emma T Watson
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | - Qiang Cui
- Department of Chemistry, Boston University, Boston, MA, 02215, USA
| | - Edwin R Chapman
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin-Madison, Madison, WI, 53705, USA.
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Mehta N, Mondal S, Watson ET, Cui Q, Chapman ER. The juxtamembrane linker of synaptotagmin 1 regulates Ca 2+ binding via liquid-liquid phase separation. bioRxiv 2023:2023.08.11.551903. [PMID: 37609296 PMCID: PMC10441399 DOI: 10.1101/2023.08.11.551903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/24/2023]
Abstract
Synaptotagmin (syt) 1, a Ca2+ sensor for synaptic vesicle exocytosis, functions in vivo as a multimer. Syt1 senses Ca2+ via tandem C2-domains that are connected to a single transmembrane domain via a juxtamembrane linker. Here, we show that this linker segment harbors a lysine-rich, intrinsically disordered region that is necessary and sufficient to mediate liquid-liquid phase separation (LLPS). Interestingly, condensate formation negatively regulates the Ca2+-sensitivity of syt1. Moreover, Ca2+ and anionic phospholipids facilitate the observed phase separation, and increases in [Ca2+]i promote the fusion of syt1 droplets in living cells. Together, these observations suggest a condensate-mediated feedback loop that serves to fine-tune the ability of syt1 to trigger release, via alterations in Ca2+ binding activity and potentially through the impact of LLPS on membrane curvature during fusion reactions. In summary, the juxtamembrane linker of syt1 emerges as a regulator of syt1 function by driving self-association via LLPS.
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Affiliation(s)
- Nikunj Mehta
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin–Madison, Madison, WI 53705, United States
| | - Sayantan Mondal
- Department of Chemistry, Boston University, Boston, MA 02215, United States
| | - Emma T. Watson
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin–Madison, Madison, WI 53705, United States
| | - Qiang Cui
- Department of Chemistry, Boston University, Boston, MA 02215, United States
| | - Edwin R. Chapman
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin–Madison, Madison, WI 53705, United States
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Watson ET, Pauers MM, Seibert MJ, Vevea JD, Chapman ER. Synaptic vesicle proteins are selectively delivered to axons in mammalian neurons. eLife 2023; 12:e82568. [PMID: 36729040 PMCID: PMC9894587 DOI: 10.7554/elife.82568] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2022] [Accepted: 01/11/2023] [Indexed: 02/03/2023] Open
Abstract
Neurotransmitter-filled synaptic vesicles (SVs) mediate synaptic transmission and are a hallmark specialization in neuronal axons. Yet, how SV proteins are sorted to presynaptic nerve terminals remains the subject of debate. The leading model posits that these proteins are randomly trafficked throughout neurons and are selectively retained in presynaptic boutons. Here, we used the RUSH (retention using selective hooks) system, in conjunction with HaloTag labeling approaches, to study the egress of two distinct transmembrane SV proteins, synaptotagmin 1 and synaptobrevin 2, from the soma of mature cultured rat and mouse neurons. For these studies, the SV reporter constructs were expressed at carefully controlled, very low levels. In sharp contrast to the selective retention model, both proteins selectively and specifically entered axons with minimal entry into dendrites. However, even moderate overexpression resulted in the spillover of SV proteins into dendrites, potentially explaining the origin of previous non-polarized transport models, revealing the limited, saturable nature of the direct axonal trafficking pathway. Moreover, we observed that SV constituents were first delivered to the presynaptic plasma membrane before incorporation into SVs. These experiments reveal a new-found membrane trafficking pathway, for SV proteins, in classically polarized mammalian neurons and provide a glimpse at the first steps of SV biogenesis.
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Affiliation(s)
- Emma T Watson
- Department of Neuroscience, University of Wisconsin-MadisonMadisonUnited States
- Howard Hughes Medical InstituteMadisonUnited States
| | - Michaela M Pauers
- Department of Neuroscience, University of Wisconsin-MadisonMadisonUnited States
- Howard Hughes Medical InstituteMadisonUnited States
| | - Michael J Seibert
- Department of Neuroscience, University of Wisconsin-MadisonMadisonUnited States
- Howard Hughes Medical InstituteMadisonUnited States
| | - Jason D Vevea
- Department of Neuroscience, University of Wisconsin-MadisonMadisonUnited States
- Howard Hughes Medical InstituteMadisonUnited States
| | - Edwin R Chapman
- Department of Neuroscience, University of Wisconsin-MadisonMadisonUnited States
- Howard Hughes Medical InstituteMadisonUnited States
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Ruhl DA, Bomba-Warczak E, Watson ET, Bradberry MM, Peterson TA, Basu T, Frelka A, Evans CS, Briguglio JS, Basta T, Stowell MHB, Savas JN, Roopra A, Pearce RA, Piper RC, Chapman ER. Synaptotagmin 17 controls neurite outgrowth and synaptic physiology via distinct cellular pathways. Nat Commun 2019; 10:3532. [PMID: 31387992 PMCID: PMC6684635 DOI: 10.1038/s41467-019-11459-4] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Accepted: 07/13/2019] [Indexed: 12/28/2022] Open
Abstract
The synaptotagmin (syt) proteins have been widely studied for their role in regulating fusion of intracellular vesicles with the plasma membrane. Here we report that syt-17, an unusual isoform of unknown function, plays no role in exocytosis, and instead plays multiple roles in intracellular membrane trafficking. Syt-17 is localized to the Golgi complex in hippocampal neurons, where it coordinates import of vesicles from the endoplasmic reticulum to support neurite outgrowth and facilitate axon regrowth after injury. Further, we discovered a second pool of syt-17 on early endosomes in neurites. Loss of syt-17 disrupts endocytic trafficking, resulting in the accumulation of excess postsynaptic AMPA receptors and defective synaptic plasticity. Two distinct pools of syt-17 thus control two crucial, independent membrane trafficking pathways in neurons. Function of syt-17 appears to be one mechanism by which neurons have specialized their secretory and endosomal systems to support the demands of synaptic communication over sprawling neurite arbors. The functional role of synaptotagmin-17 (syt-17) has remained unanswered. In this study, authors demonstrate that syt-17 exists in two distinct pools in hippocampal neurons (Golgi complex and early endosomes), where it served two completely independent functions: controlling neurite outgrowth and synaptic physiology
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Affiliation(s)
- David A Ruhl
- Department of Neuroscience, University of Wisconsin, Madison, WI, 53706, USA
| | - Ewa Bomba-Warczak
- Department of Neurology, Feinberg School of Medicine, Northwestern University, Chicago, IL, 60611, USA
| | - Emma T Watson
- Department of Neuroscience, University of Wisconsin, Madison, WI, 53706, USA
| | - Mazdak M Bradberry
- Department of Neuroscience, University of Wisconsin, Madison, WI, 53706, USA
| | - Tabitha A Peterson
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA, 52242, USA
| | - Trina Basu
- Department of Neuroscience, University of Wisconsin, Madison, WI, 53706, USA
| | - Alyssa Frelka
- Department of Anesthesiology, University of Wisconsin, Madison, WI, 53706, USA
| | - Chantell S Evans
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Joseph S Briguglio
- Department of Neuroscience, University of Wisconsin, Madison, WI, 53706, USA
| | - Tamara Basta
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, CO, 80309, USA
| | - Michael H B Stowell
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, CO, 80309, USA
| | - Jeffrey N Savas
- Department of Neurology, Feinberg School of Medicine, Northwestern University, Chicago, IL, 60611, USA
| | - Avtar Roopra
- Department of Neuroscience, University of Wisconsin, Madison, WI, 53706, USA
| | - Robert A Pearce
- Department of Anesthesiology, University of Wisconsin, Madison, WI, 53706, USA
| | - Robert C Piper
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA, 52242, USA
| | - Edwin R Chapman
- Department of Neuroscience, University of Wisconsin, Madison, WI, 53706, USA. .,Howard Hughes Medical Institute, Chevy Chase, MD, 20815, USA.
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