scholarly journals Synaptotagmin rings as high sensitivity regulators of synaptic vesicle docking and fusion

2021 ◽  
Author(s):  
Jie Zhu ◽  
Zachary A McDargh ◽  
Feng Li ◽  
Shyam Krishnakumar ◽  
James E Rothman ◽  
...  
Keyword(s):  
Synaptic Vesicle ◽  
Plasma Membranes ◽  
Calcium Influx ◽  
High Sensitivity ◽  
Bulk Solution ◽  
Membrane Composition ◽  
Ring Conformation ◽  
Anionic Phospholipid ◽  
Vesicle Docking ◽  
Phospholipid Monolayers

Synchronous release at neuronal synapses is accomplished by a machinery that senses calcium influx and fuses the synaptic vesicle and plasma membranes to release neurotransmitters. Previous studies suggested the calcium sensor Synaptotagmin (Syt) is a facilitator of vesicle docking and both a facilitator and inhibitor of fusion. On phospholipid monolayers, the Syt C2AB domain spontaneously oligomerized into rings that are disassembled by Ca2+, suggesting Syt rings may clamp fusion as membrane-separating "washers" until Ca2+-mediated disassembly triggers fusion and release (Wang et al., 2014). Here we combined mathematical modeling with experiment to measure mechanical properties of Syt rings and to test this mechanism. Consistent with experiment, the model quantitatively recapitulates observed Syt ring-induced dome and volcano shapes on phospholipid monolayers, and predicts rings are stabilized by anionic phospholipid bilayers or bulk solution with ATP. The selected ring conformation is highly sensitive to membrane composition and bulk ATP levels, a property that may regulate vesicle docking and fusion in ATP-rich synaptic terminals. We find the Syt molecules hosted by a synaptic vesicle oligomerize into a halo, unbound from the vesicle, but in proximity to sufficiently PIP2-rich plasma membrane (PM) domains the PM-bound trans Syt ring conformation is preferred. Thus, the Syt halo serves as landing gear for spatially directed docking at PIP2-rich sites that define the active zones of exocytotic release, positioning the Syt ring to clamp fusion and await calcium. Our results suggest the Syt ring is both a Ca2+-sensitive fusion clamp and a high-fidelity sensor for directed docking.

scholarly journals Membrane bridging by Munc13-1 is crucial for neurotransmitter release

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Bradley Quade ◽  
Marcial Camacho ◽  
Xiaowei Zhao ◽  
Marta Orlando ◽  
Thorsten Trimbuch ◽  
...  
Keyword(s):  
Synaptic Vesicle ◽  
Neurotransmitter Release ◽  
Plasma Membranes ◽  
Central Function ◽  
Vesicle Docking ◽  
Physiological Relevance ◽  
Residue Substitution ◽  
Liposome Fusion ◽  
Membrane Binding Sites

Munc13-1 plays a crucial role in neurotransmitter release. We recently proposed that the C-terminal region encompassing the C1, C2B, MUN and C2C domains of Munc13-1 (C1C2BMUNC2C) bridges the synaptic vesicle and plasma membranes through interactions involving the C2C domain and the C1-C2B region. However, the physiological relevance of this model has not been demonstrated. Here we show that C1C2BMUNC2C bridges membranes through opposite ends of its elongated structure. Mutations in putative membrane-binding sites of the C2C domain disrupt the ability of C1C2BMUNC2C to bridge liposomes and to mediate liposome fusion in vitro. These mutations lead to corresponding disruptive effects on synaptic vesicle docking, priming, and Ca2+-triggered neurotransmitter release in mouse neurons. Remarkably, these effects include an almost complete abrogation of release by a single residue substitution in this 200 kDa protein. These results show that bridging the synaptic vesicle and plasma membranes is a central function of Munc13-1.

scholarly journals CancerGram: An Effective Classifier for Differentiating Anticancer from Antimicrobial Peptides

Pharmaceutics ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 1045
Author(s):  
Michał Burdukiewicz ◽  
Katarzyna Sidorczuk ◽  
Dominik Rafacz ◽  
Filip Pietluch ◽  
Mateusz Bąkała ◽  
...  
Keyword(s):  
Antimicrobial Peptides ◽  
Cancer Cells ◽  
Plasma Membranes ◽  
Therapeutic Potential ◽  
Kappa Statistic ◽  
R Package ◽  
Bioactive Molecules ◽  
Membrane Composition ◽  
Anticancer Peptides ◽  
Multicellular Organisms

Antimicrobial peptides (AMPs) constitute a diverse group of bioactive molecules that provide multicellular organisms with protection against microorganisms, and microorganisms with weaponry for competition. Some AMPs can target cancer cells; thus, they are called anticancer peptides (ACPs). Due to their small size, positive charge, hydrophobicity and amphipathicity, AMPs and ACPs interact with negatively charged components of biological membranes. AMPs preferentially permeabilize microbial membranes, but ACPs additionally target mitochondrial and plasma membranes of cancer cells. The preference towards mitochondrial membranes is explained by their membrane potential, membrane composition resulting from α-proteobacterial origin and the fact that mitochondrial targeting signals could have evolved from AMPs. Taking into account the therapeutic potential of ACPs and millions of deaths due to cancer annually, it is of vital importance to find new cationic peptides that selectively destroy cancer cells. Therefore, to reduce the costs of experimental research, we have created a robust computational tool, CancerGram, that uses n-grams and random forests for predicting ACPs. Compared to other ACP classifiers, CancerGram is the first three-class model that effectively classifies peptides into: ACPs, AMPs and non-ACPs/non-AMPs, with AU1U amounting to 0.89 and a Kappa statistic of 0.65. CancerGram is available as a web server and R package on GitHub.

scholarly journals Reconstituted synaptotagmin I mediates vesicle docking, priming, and fusion

2011 ◽  
Vol 195 (7) ◽  
pp. 1159-1170 ◽  
Author(s):  
Zhao Wang ◽  
Huisheng Liu ◽  
Yiwen Gu ◽  
Edwin R. Chapman
Keyword(s):  
Synaptic Transmission ◽  
Membrane Fusion ◽  
Synaptic Vesicle ◽  
Cytoplasmic Domain ◽  
Snare Proteins ◽  
Antagonist Activity ◽  
Vesicle Docking ◽  
Synaptotagmin I ◽  
Target Membrane

The synaptic vesicle protein synaptotagmin I (syt) promotes exocytosis via its ability to penetrate membranes in response to binding Ca2+ and through direct interactions with SNARE proteins. However, studies using full-length (FL) membrane-embedded syt in reconstituted fusion assays have yielded conflicting results, including a lack of effect, or even inhibition of fusion, by Ca2+. In this paper, we show that reconstituted FL syt promoted rapid docking of vesicles (<1 min) followed by a priming step (3–9 min) that was required for subsequent Ca2+-triggered fusion between v- and t-SNARE liposomes. Moreover, fusion occurred only when phosphatidylinositol 4,5-bisphosphate was included in the target membrane. This system also recapitulates some of the effects of syt mutations that alter synaptic transmission in neurons. Finally, we demonstrate that the cytoplasmic domain of syt exhibited mixed agonist/antagonist activity during regulated membrane fusion in vitro and in cells. Together, these findings reveal further convergence of reconstituted and cell-based systems.

scholarly journals Distinct Functions of Syntaxin-1 in Neuronal Maintenance, Synaptic Vesicle Docking, and Fusion in Mouse Neurons

2016 ◽  
Vol 36 (30) ◽  
pp. 7911-7924 ◽  
Author(s):  
Gülçin Vardar ◽  
Shuwen Chang ◽  
Marife Arancillo ◽  
Yuan-Ju Wu ◽  
Thorsten Trimbuch ◽  
...  
Keyword(s):  
Synaptic Vesicle ◽  
Vesicle Docking ◽  
Neuronal Maintenance

scholarly journals Alignment of Synaptic Vesicle Macromolecules with the Macromolecules in Active Zone Material that Direct Vesicle Docking

PLoS ONE ◽  
2013 ◽  
Vol 8 (7) ◽  
pp. e69410 ◽  
Author(s):  
Mark L. Harlow ◽  
Joseph A. Szule ◽  
Jing Xu ◽  
Jae Hoon Jung ◽  
Robert M. Marshall ◽  
...  
Keyword(s):  
Synaptic Vesicle ◽  
Active Zone ◽  
Vesicle Docking

scholarly journals Poloxamer 188 reduces the contraction-induced force decline in lumbrical muscles from mdx mice

2008 ◽  
Vol 295 (1) ◽  
pp. C146-C150 ◽  
Author(s):  
Rainer Ng ◽  
Joseph M. Metzger ◽  
Dennis R. Claflin ◽  
John A. Faulkner
Keyword(s):  
Skeletal Muscle ◽  
Plasma Membranes ◽  
Calcium Influx ◽  
Contractile Activity ◽  
Muscle Fibers ◽  
Mdx Mice ◽  
Poloxamer 188 ◽  
Influx Pathways ◽  
Lumbrical Muscles ◽  
Free Environment

Duchenne Muscular Dystrophy is a genetic disease caused by the lack of the protein dystrophin. Dystrophic muscles are highly susceptible to contraction-induced injury, and following contractile activity, have disrupted plasma membranes that allow leakage of calcium ions into muscle fibers. Because of the direct relationship between increased intracellular calcium concentration and muscle dysfunction, therapeutic outcomes may be achieved through the identification and restriction of calcium influx pathways. Our purpose was to determine the contribution of sarcolemmal lesions to the force deficits caused by contraction-induced injury in dystrophic skeletal muscles. Using isolated lumbrical muscles from dystrophic ( mdx) mice, we demonstrate for the first time that poloxamer 188 (P188), a membrane-sealing poloxamer, is effective in reducing the force deficit in a whole mdx skeletal muscle. A reduction in force deficit was also observed in mdx muscles that were exposed to a calcium-free environment. These results, coupled with previous observations of calcium entry into mdx muscle fibers during a similar contraction protocol, support the interpretation that extracellular calcium enters through sarcolemmal lesions and contributes to the force deficit observed in mdx muscles. The results provide a basis for potential therapeutic strategies directed at membrane stabilization of dystrophin-deficient skeletal muscle fibers.

scholarly journals Fusion of lysosomes to plasma membrane initiates radiation-induced apoptosis

2020 ◽  
Vol 219 (4) ◽  
Author(s):  
Charles S. Ferranti ◽  
Jin Cheng ◽  
Chris Thompson ◽  
Jianjun Zhang ◽  
Jimmy A. Rotolo ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Ionizing Radiation ◽  
Plasma Membranes ◽  
Calcium Influx ◽  
Acid Sphingomyelinase ◽  
Oxygen Species ◽  
Physical Damage ◽  
Biophysical Mechanism ◽  
Radiation Induced ◽  
Induced Apoptosis

Diverse stresses, including reactive oxygen species (ROS), ionizing radiation, and chemotherapies, activate acid sphingomyelinase (ASMase) and generate the second messenger ceramide at plasma membranes, triggering apoptosis in specific cells, such as hematopoietic cells and endothelium. Ceramide elevation drives local bilayer reorganization into ceramide-rich platforms, macrodomains (0.5–5-µm diameter) that transmit apoptotic signals. An unresolved issue is how ASMase residing within lysosomes is released extracellularly within seconds to hydrolyze sphingomyelin preferentially enriched in outer plasma membranes. Here we show that physical damage by ionizing radiation and ROS induces full-thickness membrane disruption that allows local calcium influx, membrane lysosome fusion, and ASMase release. Further, electron microscopy reveals that plasma membrane “nanopore-like” structures (∼100-nm diameter) form rapidly due to lipid peroxidation, allowing calcium entry to initiate lysosome fusion. We posit that the extent of upstream damage to mammalian plasma membranes, calibrated by severity of nanopore-mediated local calcium influx for lysosome fusion, represents a biophysical mechanism for cell death induction.

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