1
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Jiao H, Li X, Li Y, Guo Y, Hu X, Sho T, Luo Y, Wang J, Cao H, Du W, Li D, Yu L. Localized, highly efficient secretion of signaling proteins by migrasomes. Cell Res 2024; 34:572-585. [PMID: 38918584 PMCID: PMC11291916 DOI: 10.1038/s41422-024-00992-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2024] [Accepted: 06/11/2024] [Indexed: 06/27/2024] Open
Abstract
Migrasomes, enriched with signaling molecules such as chemokines, cytokines and angiogenic factors, play a pivotal role in the spatially defined delivery of these molecules, influencing critical physiological processes including organ morphogenesis and angiogenesis. The mechanism governing the accumulation of signaling molecules in migrasomes has been elusive. In this study, we show that secretory proteins, including signaling proteins, are transported into migrasomes by secretory carriers via both the constitutive and regulated secretion pathways. During cell migration, a substantial portion of these carriers is redirected to the rear of the cell and actively transported into migrasomes, driven by the actin-dependent motor protein Myosin-5a. Once at the migrasomes, these carriers fuse with the migrasome membrane through SNARE-mediated mechanisms. Inhibiting migrasome formation significantly reduces secretion, suggesting migrasomes as a principal secretion route in migrating cells. Our findings reveal a specialized, highly localized secretion paradigm in migrating cells, conceptually paralleling the targeted neurotransmitter release observed in neuronal systems.
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Affiliation(s)
- Haifeng Jiao
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Centre for Life Sciences, Beijing Frontier Research Center for Biological Structure, School of Life Sciences, Tsinghua University, Beijing, China.
| | - Xiaopeng Li
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Centre for Life Sciences, Beijing Frontier Research Center for Biological Structure, School of Life Sciences, Tsinghua University, Beijing, China
| | - Ying Li
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Centre for Life Sciences, Beijing Frontier Research Center for Biological Structure, School of Life Sciences, Tsinghua University, Beijing, China
| | - Yuting Guo
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Xiaoyu Hu
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Centre for Life Sciences, Beijing Frontier Research Center for Biological Structure, School of Life Sciences, Tsinghua University, Beijing, China
| | - Takami Sho
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Centre for Life Sciences, Beijing Frontier Research Center for Biological Structure, School of Life Sciences, Tsinghua University, Beijing, China
| | - Yiqun Luo
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Centre for Life Sciences, Beijing Frontier Research Center for Biological Structure, School of Life Sciences, Tsinghua University, Beijing, China
| | - Jinyu Wang
- SLSTU-Nikon Biological Imaging Center, Center of Biomedical Analysis, Tsinghua University, Beijing, China
| | - Huizhen Cao
- SLSTU-Nikon Biological Imaging Center, Center of Biomedical Analysis, Tsinghua University, Beijing, China
| | - Wanqing Du
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Centre for Life Sciences, Beijing Frontier Research Center for Biological Structure, School of Life Sciences, Tsinghua University, Beijing, China
| | - Dong Li
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Li Yu
- State Key Laboratory of Membrane Biology, Tsinghua University-Peking University Joint Centre for Life Sciences, Beijing Frontier Research Center for Biological Structure, School of Life Sciences, Tsinghua University, Beijing, China.
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2
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Jahn R, Cafiso DC, Tamm LK. Mechanisms of SNARE proteins in membrane fusion. Nat Rev Mol Cell Biol 2024; 25:101-118. [PMID: 37848589 DOI: 10.1038/s41580-023-00668-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/06/2023] [Indexed: 10/19/2023]
Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are a family of small conserved eukaryotic proteins that mediate membrane fusion between organelles and with the plasma membrane. SNAREs are directly or indirectly anchored to membranes. Prior to fusion, complementary SNAREs assemble between membranes with the aid of accessory proteins that provide a scaffold to initiate SNARE zippering, pulling the membranes together and mediating fusion. Recent advances have enabled the construction of detailed models describing bilayer transitions and energy barriers along the fusion pathway and have elucidated the structures of SNAREs complexed in various states with regulatory proteins. In this Review, we discuss how these advances are yielding an increasingly detailed picture of the SNARE-mediated fusion pathway, leading from first contact between the membranes via metastable non-bilayer intermediates towards the opening and expansion of a fusion pore. We describe how SNARE proteins assemble into complexes, how this assembly is regulated by accessory proteins and how SNARE complexes overcome the free energy barriers that prevent spontaneous membrane fusion.
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Affiliation(s)
- Reinhard Jahn
- Laboratory of Neurobiology, Max-Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.
| | - David C Cafiso
- Department of Chemistry, University of Virginia, Charlottesville, VA, USA
| | - Lukas K Tamm
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
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3
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Golani G, Schwarz US. High curvature promotes fusion of lipid membranes: Predictions from continuum elastic theory. Biophys J 2023; 122:1868-1882. [PMID: 37077047 PMCID: PMC10209146 DOI: 10.1016/j.bpj.2023.04.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 03/19/2023] [Accepted: 04/14/2023] [Indexed: 04/21/2023] Open
Abstract
The fusion of lipid membranes progresses through a series of hemifusion intermediates with two significant energy barriers related to the formation of stalk and fusion pore, respectively. These energy barriers determine the speed and success rate of many critical biological processes, including the fusion of highly curved membranes, for example synaptic vesicles and enveloped viruses. Here we use continuum elastic theory of lipid monolayers to determine the relationship between membrane shape and energy barriers to fusion. We find that the stalk formation energy decreases with curvature by up to 31 kBT in a 20-nm-radius vesicle compared with planar membranes and by up to 8 kBT in the fusion of highly curved, long, tubular membranes. In contrast, the fusion pore formation energy barrier shows a more complicated behavior. Immediately after stalk expansion to the hemifusion diaphragm, the fusion pore formation energy barrier is low (15-25 kBT) due to lipid stretching in the distal monolayers and increased tension in highly curved vesicles. Therefore, the opening of the fusion pore is faster. However, these stresses relax over time due to lipid flip-flop from the proximal monolayer, resulting in a larger hemifusion diaphragm and a higher fusion pore formation energy barrier, up to 35 kBT. Therefore, if the fusion pore fails to open before significant lipid flip-flop takes place, the reaction proceeds to an extended hemifusion diaphragm state, which is a dead-end configuration in the fusion process and can be used to prevent viral infections. In contrast, in the fusion of long tubular compartments, the surface tension does not accumulate due to the formation of the diaphragm, and the energy barrier for pore expansion increases with curvature by up to 11 kBT. This suggests that inhibition of polymorphic virus infection could particularly target this feature of the second barrier.
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Affiliation(s)
- Gonen Golani
- Institute for Theoretical Physics and BioQuant Center for Quantitative Biology, Heidelberg University, Heidelberg, Germany
| | - Ulrich S Schwarz
- Institute for Theoretical Physics and BioQuant Center for Quantitative Biology, Heidelberg University, Heidelberg, Germany.
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4
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Dallo S, Shin J, Zhang S, Ren Q, Bao H. Designer Nanodiscs to Probe and Reprogram Membrane Biology in Synapses. J Mol Biol 2023; 435:167757. [PMID: 35872069 PMCID: PMC9805492 DOI: 10.1016/j.jmb.2022.167757] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Revised: 07/17/2022] [Accepted: 07/18/2022] [Indexed: 02/04/2023]
Abstract
Signal transduction at the synapse is mediated by a variety of protein-lipid interactions, which are vital for the spatial and temporal regulation of synaptic vesicle biogenesis, neurotransmitter release, and postsynaptic receptor activation. Therefore, our understanding of synaptic transmission cannot be completed until the elucidation of these critical protein-lipid interactions. On this front, recent advances in nanodiscs have vastly expanded our ability to probe and reprogram membrane biology in synapses. Here, we summarize the progress of the nanodisc toolbox and discuss future directions in this exciting field.
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Affiliation(s)
- Sarah Dallo
- Department of Molecular Medicine, UF Scripps Biomedical Research, 130 Scripps Way, Jupiter 33458, FL, USA
| | - Jeehae Shin
- Department of Molecular Medicine, UF Scripps Biomedical Research, 130 Scripps Way, Jupiter 33458, FL, USA
| | - Shanwen Zhang
- Department of Molecular Medicine, UF Scripps Biomedical Research, 130 Scripps Way, Jupiter 33458, FL, USA
| | - Qian Ren
- Department of Molecular Medicine, UF Scripps Biomedical Research, 130 Scripps Way, Jupiter 33458, FL, USA
| | - Huan Bao
- Department of Molecular Medicine, UF Scripps Biomedical Research, 130 Scripps Way, Jupiter 33458, FL, USA.
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5
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Wang Y, Huang R, Chai Z, Wang C, Du X, Hang Y, Xu Y, Li J, Jiang X, Wu X, Qiao Z, Li Y, Liu B, Zhang X, Cao P, Zhu F, Zhou Z. Ca 2+ -independent transmission at the central synapse formed between dorsal root ganglion and dorsal horn neurons. EMBO Rep 2022; 23:e54507. [PMID: 36148511 PMCID: PMC9638852 DOI: 10.15252/embr.202154507] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Revised: 08/07/2022] [Accepted: 08/30/2022] [Indexed: 09/25/2023] Open
Abstract
A central principle of synaptic transmission is that action potential-induced presynaptic neurotransmitter release occurs exclusively via Ca2+ -dependent secretion (CDS). The discovery and mechanistic investigations of Ca2+ -independent but voltage-dependent secretion (CiVDS) have demonstrated that the action potential per se is sufficient to trigger neurotransmission in the somata of primary sensory and sympathetic neurons in mammals. One key question remains, however, whether CiVDS contributes to central synaptic transmission. Here, we report, in the central transmission from presynaptic (dorsal root ganglion) to postsynaptic (spinal dorsal horn) neurons in vitro, (i) excitatory postsynaptic currents (EPSCs) are mediated by glutamate transmission through both CiVDS (up to 87%) and CDS; (ii) CiVDS-mediated EPSCs are independent of extracellular and intracellular Ca2+ ; (iii) CiVDS is faster than CDS in vesicle recycling with much less short-term depression; (iv) the fusion machinery of CiVDS includes Cav2.2 (voltage sensor) and SNARE (fusion pore). Together, an essential component of activity-induced EPSCs is mediated by CiVDS in a central synapse.
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Affiliation(s)
- Yuan Wang
- State Key Laboratory of Membrane Biology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular MedicineCollege of Future TechnologyPeking UniversityBeijingChina
- Peking‐Tsinghua Center for Life SciencesPeking UniversityBeijingChina
- PKU‐IDG/McGovern Institute for Brain ResearchPeking UniversityBeijingChina
| | - Rong Huang
- State Key Laboratory of Membrane Biology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular MedicineCollege of Future TechnologyPeking UniversityBeijingChina
- Peking‐Tsinghua Center for Life SciencesPeking UniversityBeijingChina
- PKU‐IDG/McGovern Institute for Brain ResearchPeking UniversityBeijingChina
| | - Zuying Chai
- State Key Laboratory of Membrane Biology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular MedicineCollege of Future TechnologyPeking UniversityBeijingChina
- Peking‐Tsinghua Center for Life SciencesPeking UniversityBeijingChina
- PKU‐IDG/McGovern Institute for Brain ResearchPeking UniversityBeijingChina
| | - Changhe Wang
- Department of NeurologyThe First Affiliated Hospital of Xi'an Jiaotong UniversityXi'anChina
- Neuroscience Research Center, Institute of Mitochondrial Biology and Medicine, Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and TechnologyXi'an Jiaotong UniversityXi'anChina
| | - Xingyu Du
- State Key Laboratory of Membrane Biology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular MedicineCollege of Future TechnologyPeking UniversityBeijingChina
- Peking‐Tsinghua Center for Life SciencesPeking UniversityBeijingChina
- PKU‐IDG/McGovern Institute for Brain ResearchPeking UniversityBeijingChina
| | - Yuqi Hang
- State Key Laboratory of Membrane Biology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular MedicineCollege of Future TechnologyPeking UniversityBeijingChina
- Peking‐Tsinghua Center for Life SciencesPeking UniversityBeijingChina
- PKU‐IDG/McGovern Institute for Brain ResearchPeking UniversityBeijingChina
| | - Yongxin Xu
- State Key Laboratory of Membrane Biology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular MedicineCollege of Future TechnologyPeking UniversityBeijingChina
- Peking‐Tsinghua Center for Life SciencesPeking UniversityBeijingChina
- PKU‐IDG/McGovern Institute for Brain ResearchPeking UniversityBeijingChina
| | - Jie Li
- State Key Laboratory of Membrane Biology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular MedicineCollege of Future TechnologyPeking UniversityBeijingChina
- Peking‐Tsinghua Center for Life SciencesPeking UniversityBeijingChina
- PKU‐IDG/McGovern Institute for Brain ResearchPeking UniversityBeijingChina
| | - Xiaohan Jiang
- State Key Laboratory of Membrane Biology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular MedicineCollege of Future TechnologyPeking UniversityBeijingChina
- Peking‐Tsinghua Center for Life SciencesPeking UniversityBeijingChina
- PKU‐IDG/McGovern Institute for Brain ResearchPeking UniversityBeijingChina
| | - Xi Wu
- State Key Laboratory of Membrane Biology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular MedicineCollege of Future TechnologyPeking UniversityBeijingChina
- Peking‐Tsinghua Center for Life SciencesPeking UniversityBeijingChina
- PKU‐IDG/McGovern Institute for Brain ResearchPeking UniversityBeijingChina
| | - Zhongjun Qiao
- State Key Laboratory of Membrane Biology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular MedicineCollege of Future TechnologyPeking UniversityBeijingChina
- Peking‐Tsinghua Center for Life SciencesPeking UniversityBeijingChina
- PKU‐IDG/McGovern Institute for Brain ResearchPeking UniversityBeijingChina
| | - Yinglin Li
- State Key Laboratory of Membrane Biology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular MedicineCollege of Future TechnologyPeking UniversityBeijingChina
- Peking‐Tsinghua Center for Life SciencesPeking UniversityBeijingChina
- PKU‐IDG/McGovern Institute for Brain ResearchPeking UniversityBeijingChina
| | - Bing Liu
- State Key Laboratory of Membrane Biology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular MedicineCollege of Future TechnologyPeking UniversityBeijingChina
- Peking‐Tsinghua Center for Life SciencesPeking UniversityBeijingChina
- PKU‐IDG/McGovern Institute for Brain ResearchPeking UniversityBeijingChina
| | | | - Peng Cao
- National Institute of Biological SciencesBeijingChina
| | - Feipeng Zhu
- State Key Laboratory of Membrane Biology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular MedicineCollege of Future TechnologyPeking UniversityBeijingChina
- Peking‐Tsinghua Center for Life SciencesPeking UniversityBeijingChina
- PKU‐IDG/McGovern Institute for Brain ResearchPeking UniversityBeijingChina
| | - Zhuan Zhou
- State Key Laboratory of Membrane Biology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular MedicineCollege of Future TechnologyPeking UniversityBeijingChina
- Peking‐Tsinghua Center for Life SciencesPeking UniversityBeijingChina
- PKU‐IDG/McGovern Institute for Brain ResearchPeking UniversityBeijingChina
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6
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Zhang Y, Ma L, Bao H. Energetics, kinetics, and pathways of SNARE assembly in membrane fusion. Crit Rev Biochem Mol Biol 2022; 57:443-460. [PMID: 36151854 PMCID: PMC9588726 DOI: 10.1080/10409238.2022.2121804] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Fusion of transmitter-containing vesicles with plasma membranes at the synaptic and neuromuscular junctions mediates neurotransmission and muscle contractions, respectively, thereby underlying all thoughts and actions. The fusion process is driven by the coupled folding and assembly of three synaptic SNARE proteins--syntaxin-1 and SNAP-25 on the target plasma membrane (t-SNAREs) and VAMP2 on the vesicular membrane (v-SNARE) into a four-helix bundle. Their assembly is chaperoned by Munc18-1 and many other proteins to achieve the speed and accuracy required for neurotransmission. However, the physiological pathway of SNARE assembly and its coupling to membrane fusion remains unclear. Here, we review recent progress in understanding SNARE assembly and membrane fusion, with a focus on results obtained by single-molecule manipulation approaches and electric recordings of single fusion pores. We describe two pathways of synaptic SNARE assembly, their associated intermediates, energetics, and kinetics. Assembly of the three SNAREs in vitro begins with the formation of a t-SNARE binary complex, on which VAMP2 folds in a stepwise zipper-like fashion. Munc18-1 significantly alters the SNARE assembly pathway: syntaxin-1 and VAMP2 first bind on the surface of Munc18-1 to form a template complex, with which SNAP-25 associates to conclude SNARE assembly and displace Munc18-1. During membrane fusion, multiple trans-SNARE complexes cooperate to open a dynamic fusion pore in a manner dependent upon their copy number and zippering states. Together, these results demonstrate that stepwise and cooperative SNARE assembly drive stagewise membrane fusion.
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Affiliation(s)
- Yongli Zhang
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA;,Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06511, USA;,Conatct: and
| | - Lu Ma
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA;,Present address: Beijing National Laboratory for Condensed Matter Physics and CAS Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Huan Bao
- Department of Molecular Medicine, The Scripps Research Institute, 130 Scripps Way, Jupiter, Florida, 33458,Conatct: and
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7
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Xu H, Cai M, Gao J, Shi Y, Chen J, Wu Q, Zhang J, Jiang J, Wang H. Membrane protein density determining membrane fusion revealed by dynamic fluorescence imaging. Talanta 2021; 226:122091. [PMID: 33676648 DOI: 10.1016/j.talanta.2021.122091] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Revised: 12/31/2020] [Accepted: 01/03/2021] [Indexed: 01/04/2023]
Abstract
Membrane fusion is fundamental to biological activity of cells, so disclosingits relevant mechanism is very important for understanding various cell functions. Although artificial model systems have been developed to uncover the mechanism of membrane fusion, key factors determining the mode of membrane fusion remain unclear. Based on the construction of different types of liposome vesicles, we used a dynamic fluorescence imaging method to investigate the effect of membrane protein distribution density on membrane fusion. Time-resolved imaging revealed that protein-free pure phospholipid vesicles themselves occurred full membrane fusion. Moreover, we prepared proteoliposomes with increasing protein-to-lipid ratio to better reflect the characteristic of membrane structure in vivo. Our data showed that pure phospholipid vesicles no longer fused with the proteoliposomes that in a higher protein proportion, indicating dense membrane proteins may hinder membrane fusion. A further comparative analysis of the interactions of pure phospholipid vesicles with the cell membrane / giant plasma membrane vesicles (GPMVs) / protein-free giant unilamellar vesicles (GUVs) confirmed the inhibitory effect of dense membrane proteins on membrane fusion. Our work demonstrates the membrane protein density influences the mode of membrane fusion and lays a foundation for constructing quasi-native membrane fusion models in vitro.
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Affiliation(s)
- Haijiao Xu
- State Key Laboratory of Electroanalytical Chemistry, Research Center of Biomembranomics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, PR China; Graduate University of Chinese Academy of Sciences, Beijing, 100049, PR China
| | - Mingjun Cai
- State Key Laboratory of Electroanalytical Chemistry, Research Center of Biomembranomics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, PR China
| | - Jing Gao
- State Key Laboratory of Electroanalytical Chemistry, Research Center of Biomembranomics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, PR China
| | - Yan Shi
- State Key Laboratory of Electroanalytical Chemistry, Research Center of Biomembranomics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, PR China
| | - Junling Chen
- School of Chemistry and Chemical Engineering, Wuhan University of Science and Technology, Wuhan, Hubei, 430081, PR China
| | - Qiang Wu
- School of Chemistry and Chemical Engineering, Wuhan University of Science and Technology, Wuhan, Hubei, 430081, PR China
| | - Jinrui Zhang
- State Key Laboratory of Electroanalytical Chemistry, Research Center of Biomembranomics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, PR China
| | - Junguang Jiang
- State Key Laboratory of Electroanalytical Chemistry, Research Center of Biomembranomics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, PR China
| | - Hongda Wang
- State Key Laboratory of Electroanalytical Chemistry, Research Center of Biomembranomics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, PR China; University of Science and Technology of China, Hefei, Anhui, 230026, PR China; Laboratory for Marine Biology and Biotechnology, Qing Dao National Laboratory for Marine Science and Technology, Qingdao, Shandong, 266237, PR China.
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8
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Winner BM, Bodt SML, McNutt PM. Special Delivery: Potential Mechanisms of Botulinum Neurotoxin Uptake and Trafficking within Motor Nerve Terminals. Int J Mol Sci 2020; 21:ijms21228715. [PMID: 33218099 PMCID: PMC7698961 DOI: 10.3390/ijms21228715] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2020] [Revised: 11/11/2020] [Accepted: 11/16/2020] [Indexed: 02/06/2023] Open
Abstract
Botulinum neurotoxins (BoNTs) are highly potent, neuroparalytic protein toxins that block the release of acetylcholine from motor neurons and autonomic synapses. The unparalleled toxicity of BoNTs results from the highly specific and localized cleavage of presynaptic proteins required for nerve transmission. Currently, the only pharmacotherapy for botulism is prophylaxis with antitoxin, which becomes progressively less effective as symptoms develop. Treatment for symptomatic botulism is limited to supportive care and artificial ventilation until respiratory function spontaneously recovers, which can take weeks or longer. Mechanistic insights into intracellular toxin behavior have progressed significantly since it was shown that toxins exploit synaptic endocytosis for entry into the nerve terminal, but fundamental questions about host-toxin interactions remain unanswered. Chief among these are mechanisms by which BoNT is internalized into neurons and trafficked to sites of molecular toxicity. Elucidating how receptor-bound toxin is internalized and conditions under which the toxin light chain engages with target SNARE proteins is critical for understanding the dynamics of intoxication and identifying novel therapeutics. Here, we discuss the implications of newly discovered modes of synaptic vesicle recycling on BoNT uptake and intraneuronal trafficking.
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Affiliation(s)
- Brittany M. Winner
- United States Army Medical Research Institute of Chemical Defense, Gunpowder, MD 21047, USA;
| | - Skylar M. L. Bodt
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA 17033, USA;
| | - Patrick M. McNutt
- Wake Forest Institute for Regenerative Medicine, Wake Forest University, Winston-Salem, NC 27101, USA
- Correspondence:
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9
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Dhara M, Mantero Martinez M, Makke M, Schwarz Y, Mohrmann R, Bruns D. Synergistic actions of v-SNARE transmembrane domains and membrane-curvature modifying lipids in neurotransmitter release. eLife 2020; 9:e55152. [PMID: 32391794 PMCID: PMC7239655 DOI: 10.7554/elife.55152] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Accepted: 05/07/2020] [Indexed: 01/01/2023] Open
Abstract
Vesicle fusion is mediated by assembly of SNARE proteins between opposing membranes. While previous work suggested an active role of SNARE transmembrane domains (TMDs) in promoting membrane merger (Dhara et al., 2016), the underlying mechanism remained elusive. Here, we show that naturally-occurring v-SNARE TMD variants differentially regulate fusion pore dynamics in mouse chromaffin cells, indicating TMD flexibility as a mechanistic determinant that facilitates transmitter release from differentially-sized vesicles. Membrane curvature-promoting phospholipids like lysophosphatidylcholine or oleic acid profoundly alter pore expansion and fully rescue the decelerated fusion kinetics of TMD-rigidifying VAMP2 mutants. Thus, v-SNARE TMDs and phospholipids cooperate in supporting membrane curvature at the fusion pore neck. Oppositely, slowing of pore kinetics by the SNARE-regulator complexin-2 withstands the curvature-driven speeding of fusion, indicating that pore evolution is tightly coupled to progressive SNARE complex formation. Collectively, TMD-mediated support of membrane curvature and SNARE force-generated membrane bending promote fusion pore formation and expansion.
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Affiliation(s)
- Madhurima Dhara
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland UniversityHomburgGermany
| | - Maria Mantero Martinez
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland UniversityHomburgGermany
| | - Mazen Makke
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland UniversityHomburgGermany
| | - Yvonne Schwarz
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland UniversityHomburgGermany
| | - Ralf Mohrmann
- Institute for Physiology, Otto-von-Guericke UniversityMagdeburgGermany
| | - Dieter Bruns
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland UniversityHomburgGermany
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10
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Xu H, Gao J, Cai M, Chen J, Zhang Q, Li H, Wang H. Structural Mechanism Analysis of Orderly and Efficient Vesicle Transport by High-Resolution Imaging and Fluorescence Tracking. Anal Chem 2020; 92:6555-6563. [PMID: 32290652 DOI: 10.1021/acs.analchem.0c00197] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The orderly organelle interaction network is essential for normal biological activity of cells. However, the mechanism of orderly organelle interaction remains elusive. In this report, we analyzed the structure characteristics of the cell membrane, endocytic vesicles, and the Golgi membrane through a high-resolution imaging technique and further comprehensively investigated the vesicle-transport process via epidermal growth factor receptor endocytosis and a recycling pathway using a real-time fluorescence tracing method. Our data suggest that orderly vesicle transport is due to protein protrusion from the outer surface of endocytic vesicles and that full membrane fusion between homotypic endocytic vesicles is a result of the rough outer surface. Finally, the kiss-and-run method, which is utilized by endocytic vesicles to communicate with the trans-Golgi network (TGN) is attributed to a dense protein layer at the outer surface of the TGN. In summary, by combining static structural analysis with dynamic tracing, we elucidate the mechanism of orderly vesicle transport from the overall structural features of the membrane. This work provides insight into the structural mechanisms underlying vital biological processes involving organelle interactions at the molecular level.
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Affiliation(s)
- Haijiao Xu
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P.R. China.,Graduate University of Chinese Academy of Sciences, Beijing 100049, P.R. China
| | - Jing Gao
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P.R. China
| | - Mingjun Cai
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P.R. China
| | - Junling Chen
- School of Chemistry and Chemical Engineering, Wuhan University of Science and Technology, Wuhan, Hubei 430081, P.R. China
| | - Qingrong Zhang
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P.R. China
| | - Hongru Li
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P.R. China.,University of Science and Technology of China, Hefei, Anhui 230026, P.R. China
| | - Hongda Wang
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P.R. China.,Laboratory for Marine Biology and Biotechnology, Qing Dao National Laboratory for Marine Science and Technology, Qingdao, Shandong 266237, P.R. China.,University of Science and Technology of China, Hefei, Anhui 230026, P.R. China
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11
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Lu T, Guo H. How the Membranes Fuse: From Spontaneous to Induced. ADVANCED THEORY AND SIMULATIONS 2019. [DOI: 10.1002/adts.201900032] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Teng Lu
- Beijing National Laboratory for Molecular SciencesJoint Laboratory of Polymer Sciences and MaterialsState Key Laboratory of Polymer Physics and ChemistryInstitute of Chemistry, Chinese Academy of Sciences Beijing 100190 China
| | - Hongxia Guo
- Beijing National Laboratory for Molecular SciencesJoint Laboratory of Polymer Sciences and MaterialsState Key Laboratory of Polymer Physics and ChemistryInstitute of Chemistry, Chinese Academy of Sciences Beijing 100190 China
- Division of Polymer Science and MaterialsSchool of Chemical SciencesUniversity of Chinese Academy of Sciences Beijing 100049 China
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12
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Sun Y, Huang D, Chen X. Dynamic regulation of plasmodesmatal permeability and its application to horticultural research. HORTICULTURE RESEARCH 2019; 6:47. [PMID: 30962940 PMCID: PMC6441653 DOI: 10.1038/s41438-019-0129-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 01/17/2019] [Accepted: 01/18/2019] [Indexed: 05/10/2023]
Abstract
Effective cell-to-cell communication allows plants to fine-tune their developmental processes in accordance with the prevailing environmental stimuli. Plasmodesmata (PD) are intercellular channels that span the plant cell wall and serve as cytoplasmic bridges to facilitate efficient exchange of signaling molecules between neighboring cells. The identification of PD-associated proteins and the subsequent elucidation of the regulation of PD structure have provided vital insights into the role of PD architecture in enforcing crucial cellular processes, including callose deposition, ER-Golgi-based secretion, cytoskeleton dynamics, membrane lipid raft organization, chloroplast metabolism, and cell wall formation. In this review, we summarize the emerging discoveries from recent studies that elucidated the regulatory mechanisms involved in PD biogenesis and the dynamics of PD opening-closure. Retrospectively, PD-mediated cell-to-cell communication has been implicated in diverse cellular and physiological processes that are fundamental for the development of horticultural plants. The potential application of PD biotechnological engineering represents a powerful approach for improving agronomic traits in horticultural crops in the future.
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Affiliation(s)
- Yanbiao Sun
- College of Life Science and Fujian Provincial Key Laboratory of Haixia Applied Plant Systems Biology, Fujian Agriculture and Forestry University, Fuzhou, Fujian China
- Haixia Institute of Science and Technology, Horticultural Plant Biology and Metabolomics Center, Fujian Agriculture and Forestry University, Fuzhou, 350002 China
| | - Dingquan Huang
- Haixia Institute of Science and Technology, Horticultural Plant Biology and Metabolomics Center, Fujian Agriculture and Forestry University, Fuzhou, 350002 China
| | - Xu Chen
- Haixia Institute of Science and Technology, Horticultural Plant Biology and Metabolomics Center, Fujian Agriculture and Forestry University, Fuzhou, 350002 China
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13
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Shen C, Liu Y, Yu H, Gulbranson DR, Kogut I, Bilousova G, Zhang C, Stowell MHB, Shen J. The N-peptide-binding mode is critical to Munc18-1 function in synaptic exocytosis. J Biol Chem 2018; 293:18309-18317. [PMID: 30275014 DOI: 10.1074/jbc.ra118.005254] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Revised: 09/25/2018] [Indexed: 01/09/2023] Open
Abstract
Sec1/Munc18 (SM) proteins promote intracellular vesicle fusion by binding to N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs). A key SNARE-binding mode of SM proteins involves the N-terminal peptide (N-peptide) motif of syntaxin, a SNARE subunit localized to the target membrane. In in vitro membrane fusion assays, inhibition of N-peptide motif binding previously has been shown to abrogate the stimulatory function of Munc18-1, a SM protein involved in synaptic exocytosis in neurons. The physiological role of the N-peptide-binding mode, however, remains unclear. In this work, we addressed this key question using a "clogged" Munc18-1 protein, in which an ectopic copy of the syntaxin N-peptide motif was directly fused to Munc18-1. We found that the ectopic N-peptide motif blocks the N-peptide-binding pocket of Munc18-1, preventing the latter from binding to the native N-peptide motif on syntaxin-1. In a reconstituted system, we observed that clogged Munc18-1 is defective in promoting SNARE zippering. When introduced into induced neuronal cells (iN cells) derived from human pluripotent stem cells, clogged Munc18-1 failed to mediate synaptic exocytosis. As a result, both spontaneous and evoked synaptic transmission was abolished. These genetic findings provide direct evidence for the crucial role of the N-peptide-binding mode of Munc18-1 in synaptic exocytosis. We suggest that clogged SM proteins will also be instrumental in defining the physiological roles of the N-peptide-binding mode in other vesicle-fusion pathways.
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Affiliation(s)
- Chong Shen
- From the Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309
| | - Yinghui Liu
- From the Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309,; the Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing 210023, China
| | - Haijia Yu
- From the Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309,; the Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing 210023, China,.
| | - Daniel R Gulbranson
- From the Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309
| | - Igor Kogut
- the Department of Dermatology and Charles C. Gates Center for Regenerative Medicine, University of Colorado School of Medicine, Aurora, Colorado 80045, and
| | - Ganna Bilousova
- the Department of Dermatology and Charles C. Gates Center for Regenerative Medicine, University of Colorado School of Medicine, Aurora, Colorado 80045, and
| | - Chen Zhang
- the School of Basic Medical Sciences, Capital Medical University, Beijing 100069, China
| | - Michael H B Stowell
- From the Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309
| | - Jingshi Shen
- From the Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309,.
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14
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Maschi D, Klyachko VA. Spatiotemporal Regulation of Synaptic Vesicle Fusion Sites in Central Synapses. Neuron 2017; 94:65-73.e3. [DOI: 10.1016/j.neuron.2017.03.006] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Revised: 02/10/2017] [Accepted: 03/02/2017] [Indexed: 12/22/2022]
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15
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Cahill J, Rajaure M, O'Leary C, Sloan J, Marrufo A, Holt A, Kulkarni A, Hernandez O, Young R. Genetic Analysis of the Lambda Spanins Rz and Rz1: Identification of Functional Domains. G3 (BETHESDA, MD.) 2017; 7:741-753. [PMID: 28040784 PMCID: PMC5295617 DOI: 10.1534/g3.116.037192] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Accepted: 12/26/2016] [Indexed: 11/18/2022]
Abstract
Coliphage lambda proteins Rz and Rz1 are the inner membrane and outer membrane subunits of the spanin complex-a heterotetramer that bridges the periplasm and is essential for the disruption of the outer membrane during phage lysis. Recent evidence suggests the spanin complex functions by fusing the inner and outer membrane. Here, we use a genetics approach to investigate and characterize determinants of spanin function. Because Rz1 is entirely embedded in the +1 reading frame of Rz, the genes were disembedded before using random mutagenesis to construct a library of lysis-defective alleles for both genes. Surprisingly, most of the lysis-defective missense mutants exhibited normal accumulation or localization in vivo, and also were found to be normal for complex formation in vitro Analysis of the distribution and nature of single missense mutations revealed subdomains that resemble key motifs in established membrane-fusion systems, i.e., two coiled-coil domains in Rz, a proline-rich region of Rz1, and flexible linkers in both proteins. When coding sequences are aligned respective to the embedded genetic architecture of Rz1 within Rz, genetically silent domains of Rz1 correspond to mutationally sensitive domains in Rz, and vice versa, suggesting that the modular structure of the two subunits facilitated the evolutionary compression that resulted in the unique embedded gene architecture.
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Affiliation(s)
- Jesse Cahill
- Center for Phage Technology and Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843
| | - Manoj Rajaure
- Center for Phage Technology and Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843
| | - Chandler O'Leary
- Center for Phage Technology and Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843
| | - Jordan Sloan
- Center for Phage Technology and Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843
| | - Armando Marrufo
- Center for Phage Technology and Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843
| | - Ashley Holt
- Center for Phage Technology and Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843
| | - Aneesha Kulkarni
- Center for Phage Technology and Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843
| | - Oscar Hernandez
- Center for Phage Technology and Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843
| | - Ry Young
- Center for Phage Technology and Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843
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16
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Chang CW, Chiang CW, Jackson MB. Fusion pores and their control of neurotransmitter and hormone release. J Gen Physiol 2017; 149:301-322. [PMID: 28167663 PMCID: PMC5339513 DOI: 10.1085/jgp.201611724] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2016] [Revised: 01/06/2017] [Accepted: 01/19/2017] [Indexed: 11/20/2022] Open
Abstract
Chang et al. review fusion pore structure and dynamics and discuss the implications for hormone and neurotransmitter release Ca2+-triggered exocytosis functions broadly in the secretion of chemical signals, enabling neurons to release neurotransmitters and endocrine cells to release hormones. The biological demands on this process can vary enormously. Although synapses often release neurotransmitter in a small fraction of a millisecond, hormone release can be orders of magnitude slower. Vesicles usually contain multiple signaling molecules that can be released selectively and conditionally. Cells are able to control the speed, concentration profile, and content selectivity of release by tuning and tailoring exocytosis to meet different biological demands. Much of this regulation depends on the fusion pore—the aqueous pathway by which molecules leave a vesicle and move out into the surrounding extracellular space. Studies of fusion pores have illuminated how cells regulate secretion. Furthermore, the formation and growth of fusion pores serve as a readout for the progress of exocytosis, thus revealing key kinetic stages that provide clues about the underlying mechanisms. Herein, we review the structure, composition, and dynamics of fusion pores and discuss the implications for molecular mechanisms as well as for the cellular regulation of neurotransmitter and hormone release.
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Affiliation(s)
- Che-Wei Chang
- Department of Neuroscience, University of Wisconsin-Madison, Madison, WI 53705
| | - Chung-Wei Chiang
- Department of Neuroscience, University of Wisconsin-Madison, Madison, WI 53705
| | - Meyer B Jackson
- Department of Neuroscience, University of Wisconsin-Madison, Madison, WI 53705
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17
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Extended synaptotagmins are Ca2+-dependent lipid transfer proteins at membrane contact sites. Proc Natl Acad Sci U S A 2016; 113:4362-7. [PMID: 27044075 DOI: 10.1073/pnas.1517259113] [Citation(s) in RCA: 99] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Organelles are in constant communication with each other through exchange of proteins (mediated by trafficking vesicles) and lipids [mediated by both trafficking vesicles and lipid transfer proteins (LTPs)]. It has long been known that vesicle trafficking can be tightly regulated by the second messenger Ca(2+), allowing membrane protein transport to be adjusted according to physiological demands. However, it remains unclear whether LTP-mediated lipid transport can also be regulated by Ca(2+) In this work, we show that extended synaptotagmins (E-Syts), poorly understood membrane proteins at endoplasmic reticulum-plasma membrane contact sites, are Ca(2+)-dependent LTPs. Using both recombinant and endogenous mammalian proteins, we discovered that E-Syts transfer glycerophospholipids between membrane bilayers in the presence of Ca(2+) E-Syts use their lipid-accommodating synaptotagmin-like mitochondrial lipid binding protein (SMP) domains to transfer lipids. However, the SMP domains themselves cannot transport lipids unless the two membranes are tightly tethered by Ca(2+)-bound C2 domains. Strikingly, the Ca(2+)-regulated lipid transfer activity of E-Syts was fully recapitulated when the SMP domain was fused to the cytosolic domain of synaptotagmin-1, the Ca(2+)sensor in synaptic vesicle fusion, indicating that a common mechanism of membrane tethering governs the Ca(2+)regulation of lipid transfer and vesicle fusion. Finally, we showed that microsomal vesicles isolated from mammalian cells contained robust Ca(2+)-dependent lipid transfer activities, which were mediated by E-Syts. These findings established E-Syts as a novel class of LTPs and showed that LTP-mediated lipid trafficking, like vesicular transport, can be subject to tight Ca(2+)regulation.
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18
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Han J, Pluhackova K, Bruns D, Böckmann RA. Synaptobrevin transmembrane domain determines the structure and dynamics of the SNARE motif and the linker region. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:855-65. [DOI: 10.1016/j.bbamem.2016.01.030] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2015] [Revised: 01/06/2016] [Accepted: 01/27/2016] [Indexed: 12/29/2022]
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19
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Chang CW, Jackson MB. Synaptobrevin transmembrane domain influences exocytosis by perturbing vesicle membrane curvature. Biophys J 2016; 109:76-84. [PMID: 26153704 DOI: 10.1016/j.bpj.2015.05.021] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Revised: 04/29/2015] [Accepted: 05/11/2015] [Indexed: 01/12/2023] Open
Abstract
Membrane fusion requires that nearly flat lipid bilayers deform into shapes with very high curvature. This makes membrane bending a critical force in determining fusion mechanisms. A lipid bilayer will bend spontaneously when material is distributed asymmetrically between its two monolayers, and its spontaneous curvature (C0) will influence the stability of curved fusion intermediates. Prior work on Ca(2+)-triggered exocytosis revealed that fusion pore lifetime (τ) varies with vesicle content (Q), and showed that this relation reflects membrane bending energetics. Lipids that alter C0 change the dependence of τ on Q. These results suggested that the greater stability of an initial exocytotic fusion pore associated with larger vesicles reflects the need to bend more membrane during fusion pore dilation. In this study, we explored the possibility of manipulating C0 by mutating the transmembrane domain (TMD) of the vesicle membrane protein synaptobrevin 2 (syb2). Amperometric measurements of exocytosis in mouse chromaffin cells revealed that syb2 TMD mutations altered the relation between τ and Q. The effects of these mutations showed a striking periodicity, changing sign as the structural perturbation moved through the inner and outer leaflets. Some glycine and charge mutations also influenced the dependence of τ on Q in a manner consistent with expected changes in C0. These results suggest that side chains in the syb2 TMD influence the kinetics of exocytosis by perturbing the packing of the surrounding lipids. The present results support the view that membrane bending occurs during fusion pore expansion rather than during fusion pore formation. This supports the view of an initial fusion pore through two relatively flat membranes formed by protein.
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Affiliation(s)
- Che-Wei Chang
- Department of Neuroscience, Physiology Graduate Training Program, University of Wisconsin, Madison, Wisconsin
| | - Meyer B Jackson
- Department of Neuroscience, Physiology Graduate Training Program, University of Wisconsin, Madison, Wisconsin.
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20
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Woo SY, Lee H. All-atom simulations and free-energy calculations of coiled-coil peptides with lipid bilayers: binding strength, structural transition, and effect on lipid dynamics. Sci Rep 2016; 6:22299. [PMID: 26926570 PMCID: PMC4772085 DOI: 10.1038/srep22299] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2015] [Accepted: 02/11/2016] [Indexed: 01/04/2023] Open
Abstract
Peptides E and K, which are synthetic coiled-coil peptides for membrane fusion, were simulated with lipid bilayers composed of lipids and cholesterols at different ratios using all-atom models. We first calculated free energies of binding from umbrella sampling simulations, showing that both E and K peptides tend to adsorb onto the bilayer surface, which occurs more strongly in the bilayer composed of smaller lipid headgroups. Then, unrestrained simulations show that K peptides more deeply insert into the bilayer with partially retaining the helical structure, while E peptides less insert and predominantly become random coils, indicating the structural transition from helices to random coils, in quantitative agreement with experiments. This is because K peptides electrostatically interact with lipid phosphates, as well as because hydrocarbons of lysines of K peptide are longer than those of glutamic acids of E peptide and thus form stronger hydrophobic interactions with lipid tails. This deeper insertion of K peptide increases the bilayer dynamics and a vacancy below the peptide, leading to the rearrangement of smaller lipids. These findings help explain the experimentally observed or proposed differences in the insertion depth, binding strength, and structural transition of E and K peptides, and support the snorkeling effect.
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Affiliation(s)
- Sun Young Woo
- Department of Chemical Engineering, Dankook University, Yongin, 448-701, South Korea
| | - Hwankyu Lee
- Department of Chemical Engineering, Dankook University, Yongin, 448-701, South Korea
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21
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Chang CW, Chiang CW, Gaffaney JD, Chapman ER, Jackson MB. Lipid-anchored Synaptobrevin Provides Little or No Support for Exocytosis or Liposome Fusion. J Biol Chem 2015; 291:2848-57. [PMID: 26663078 DOI: 10.1074/jbc.m115.701169] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Indexed: 12/11/2022] Open
Abstract
SNARE proteins catalyze many forms of biological membrane fusion, including Ca(2+)-triggered exocytosis. Although fusion mediated by SNAREs generally involves proteins anchored to each fusing membrane by a transmembrane domain (TMD), the role of TMDs remains unclear, and previous studies diverge on whether SNAREs can drive fusion without a TMD. This issue is important because it relates to the question of the structure and composition of the initial fusion pore, as well as the question of whether SNAREs mediate fusion solely by creating close proximity between two membranes versus a more active role in transmitting force to the membrane to deform and reorganize lipid bilayer structure. To test the role of membrane attachment, we generated four variants of the synaptic v-SNARE synaptobrevin-2 (syb2) anchored to the membrane by lipid instead of protein. These constructs were tested for functional efficacy in three different systems as follows: Ca(2+)-triggered dense core vesicle exocytosis, spontaneous synaptic vesicle exocytosis, and Ca(2+)-synaptotagmin-enhanced SNARE-mediated liposome fusion. Lipid-anchoring motifs harboring one or two lipid acylation sites completely failed to support fusion in any of these assays. Only the lipid-anchoring motif from cysteine string protein-α, which harbors many lipid acylation sites, provided support for fusion but at levels well below that achieved with wild type syb2. Thus, lipid-anchored syb2 provides little or no support for exocytosis, and anchoring syb2 to a membrane by a TMD greatly improves its function. The low activity seen with syb2-cysteine string protein-α may reflect a slower alternative mode of SNARE-mediated membrane fusion.
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Affiliation(s)
| | | | | | - Edwin R Chapman
- Biophysics Ph.D. Program, Howard Hughes Medical Institute, and Department of Neuroscience, University of Wisconsin, Madison, Wisconsin 53705
| | - Meyer B Jackson
- From the Physiology Ph.D. Graduate Training Program, Biophysics Ph.D. Program, Department of Neuroscience, University of Wisconsin, Madison, Wisconsin 53705
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22
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23
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Ansari IUH, Longacre MJ, Paulusma CC, Stoker SW, Kendrick MA, MacDonald MJ. Characterization of P4 ATPase Phospholipid Translocases (Flippases) in Human and Rat Pancreatic Beta Cells: THEIR GENE SILENCING INHIBITS INSULIN SECRETION. J Biol Chem 2015; 290:23110-23. [PMID: 26240149 DOI: 10.1074/jbc.m115.655027] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Indexed: 01/08/2023] Open
Abstract
The negative charge of phosphatidylserine in lipid bilayers of secretory vesicles and plasma membranes couples the domains of positively charged amino acids of secretory vesicle SNARE proteins with similar domains of plasma membrane SNARE proteins enhancing fusion of the two membranes to promote exocytosis of the vesicle contents of secretory cells. Our recent study of insulin secretory granules (ISG) (MacDonald, M. J., Ade, L., Ntambi, J. M., Ansari, I. H., and Stoker, S. W. (2015) Characterization of phospholipids in insulin secretory granules in pancreatic beta cells and their changes with glucose stimulation. J. Biol. Chem. 290, 11075-11092) suggested that phosphatidylserine and other phospholipids, such as phosphatidylethanolamine, in ISG could play important roles in docking and fusion of ISG to the plasma membrane in the pancreatic beta cell during insulin exocytosis. P4 ATPase flippases translocate primarily phosphatidylserine and, to a lesser extent, phosphatidylethanolamine across the lipid bilayers of intracellular vesicles and plasma membranes to the cytosolic leaflets of these membranes. CDC50A is a protein that forms a heterodimer with P4 ATPases to enhance their translocase catalytic activity. We found that the predominant P4 ATPases in pure pancreatic beta cells and human and rat pancreatic islets were ATP8B1, ATP8B2, and ATP9A. ATP8B1 and CDC50A were highly concentrated in ISG. ATP9A was concentrated in plasma membrane. Gene silencing of individual P4 ATPases and CDC50A inhibited glucose-stimulated insulin release in pure beta cells and in human pancreatic islets. This is the first characterization of P4 ATPases in beta cells. The results support roles for P4 ATPases in translocating phosphatidylserine to the cytosolic leaflets of ISG and the plasma membrane to facilitate the docking and fusion of ISG to the plasma membrane during insulin exocytosis.
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Affiliation(s)
- Israr-ul H Ansari
- From the Childrens Diabetes Center, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706 and
| | - Melissa J Longacre
- From the Childrens Diabetes Center, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706 and
| | - Coen C Paulusma
- the Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, 1105 BK Amsterdam, The Netherlands
| | - Scott W Stoker
- From the Childrens Diabetes Center, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706 and
| | - Mindy A Kendrick
- From the Childrens Diabetes Center, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706 and
| | - Michael J MacDonald
- From the Childrens Diabetes Center, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706 and
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24
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Gong B, Choi BK, Kim JY, Shetty D, Ko YH, Selvapalam N, Lee NK, Kim K. High Affinity Host-Guest FRET Pair for Single-Vesicle Content-Mixing Assay: Observation of Flickering Fusion Events. J Am Chem Soc 2015; 137:8908-11. [PMID: 26160008 DOI: 10.1021/jacs.5b05385] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Fluorescence-based single-vesicle fusion assays provide a powerful method for studying mechanisms underlying complex biological processes of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor)-mediated vesicle fusion and neurotransmitter release. A crucial element of these assays is the ability of the fluorescent probe(s) to reliably detect key intermediate events of fusion pore opening and content release/mixing. Here, we report a new, reliable, and efficient single-vesicle content-mixing assay using a high affinity, fluorophore tagged host-guest pair, cucurbit[7]uril-Cy3 and adamantane-Cy5 as a fluorescence resonance energy transfer (FRET) pair. The power of these probes is demonstrated by the first successful observation of flickering dynamics of the fusion pore by in vitro assay using neuronal SNARE-reconstituted vesicles.
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Affiliation(s)
- Bokyoung Gong
- †Center for Self-Assembly and Complexity (CSC), Institute for Basic Science (IBS), ‡Department of Chemistry, §School of Interdisciplinary Bioscience and Bioengineering, and ∥Department of Physics, #Division of Advanced Materials Science, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
| | - Bong-Kyu Choi
- †Center for Self-Assembly and Complexity (CSC), Institute for Basic Science (IBS), ‡Department of Chemistry, §School of Interdisciplinary Bioscience and Bioengineering, and ∥Department of Physics, #Division of Advanced Materials Science, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
| | - Jae-Yeol Kim
- †Center for Self-Assembly and Complexity (CSC), Institute for Basic Science (IBS), ‡Department of Chemistry, §School of Interdisciplinary Bioscience and Bioengineering, and ∥Department of Physics, #Division of Advanced Materials Science, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
| | - Dinesh Shetty
- †Center for Self-Assembly and Complexity (CSC), Institute for Basic Science (IBS), ‡Department of Chemistry, §School of Interdisciplinary Bioscience and Bioengineering, and ∥Department of Physics, #Division of Advanced Materials Science, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
| | - Young Ho Ko
- †Center for Self-Assembly and Complexity (CSC), Institute for Basic Science (IBS), ‡Department of Chemistry, §School of Interdisciplinary Bioscience and Bioengineering, and ∥Department of Physics, #Division of Advanced Materials Science, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
| | - Narayanan Selvapalam
- †Center for Self-Assembly and Complexity (CSC), Institute for Basic Science (IBS), ‡Department of Chemistry, §School of Interdisciplinary Bioscience and Bioengineering, and ∥Department of Physics, #Division of Advanced Materials Science, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
| | - Nam Ki Lee
- †Center for Self-Assembly and Complexity (CSC), Institute for Basic Science (IBS), ‡Department of Chemistry, §School of Interdisciplinary Bioscience and Bioengineering, and ∥Department of Physics, #Division of Advanced Materials Science, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
| | - Kimoon Kim
- †Center for Self-Assembly and Complexity (CSC), Institute for Basic Science (IBS), ‡Department of Chemistry, §School of Interdisciplinary Bioscience and Bioengineering, and ∥Department of Physics, #Division of Advanced Materials Science, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
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25
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Abstract
The SNARE (Soluble NSF Attachment protein REceptor) complex, which in mammalian neurosecretory cells is composed of the proteins synaptobrevin 2 (also called VAMP2), syntaxin, and SNAP-25, plays a key role in vesicle fusion. In this review, we discuss the hypothesis that, in neurosecretory cells, fusion pore formation is directly accomplished by a conformational change in the SNARE complex via movement of the transmembrane domains.
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Affiliation(s)
- Qinghua Fang
- School of Applied and Engineering Physics, Cornell University, Ithaca, New York; and Laboratory for Nanoscale Cell Biology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
| | - Manfred Lindau
- School of Applied and Engineering Physics, Cornell University, Ithaca, New York; and Laboratory for Nanoscale Cell Biology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
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26
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MacDonald MJ, Ade L, Ntambi JM, Ansari IUH, Stoker SW. Characterization of phospholipids in insulin secretory granules and mitochondria in pancreatic beta cells and their changes with glucose stimulation. J Biol Chem 2015; 290:11075-92. [PMID: 25762724 DOI: 10.1074/jbc.m114.628420] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Indexed: 01/05/2023] Open
Abstract
The lipid composition of insulin secretory granules (ISG) has never previously been thoroughly characterized. We characterized the phospholipid composition of ISG and mitochondria in pancreatic beta cells without and with glucose stimulation. The phospholipid/protein ratios of most phospholipids containing unsaturated fatty acids were higher in ISG than in whole cells and in mitochondria. The concentrations of negatively charged phospholipids, phosphatidylserine, and phosphatidylinositol in ISG were 5-fold higher than in the whole cell. In ISG phosphatidylserine, phosphatidylinositol, phosphatidylethanolamine, and sphingomyelin, fatty acids 12:0 and 14:0 were high, as were phosphatidylserine and phosphatidylinositol containing 18-carbon unsaturated FA. With glucose stimulation, the concentration of many ISG phosphatidylserines and phosphatidylinositols increased; unsaturated fatty acids in phosphatidylserine increased; and most phosphatidylethanolamines, phosphatidylcholines, sphingomyelins, and lysophosphatidylcholines were unchanged. Unsaturation and shorter fatty acid length in phospholipids facilitate curvature and fluidity of membranes, which favors fusion of membranes. Recent evidence suggests that negatively charged phospholipids, such as phosphatidylserine, act as coupling factors enhancing the interaction of positively charged regions in SNARE proteins in synaptic or secretory vesicle membrane lipid bilayers with positively charged regions in SNARE proteins in the plasma membrane lipid bilayer to facilitate docking of vesicles to the plasma membrane during exocytosis. The results indicate that ISG phospholipids are in a dynamic state and are consistent with the idea that changes in ISG phospholipids facilitate fusion of ISG with the plasma membrane-enhancing glucose-stimulated insulin exocytosis.
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Affiliation(s)
- Michael J MacDonald
- From the Children's Diabetes Center, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706 and
| | | | - James M Ntambi
- the Departments of Biochemistry and Nutritional Sciences, University of Wisconsin, Madison, Wisconsin 53706
| | - Israr-Ul H Ansari
- From the Children's Diabetes Center, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706 and
| | - Scott W Stoker
- From the Children's Diabetes Center, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706 and
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27
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Faust JE, Desai T, Verma A, Ulengin I, Sun TL, Moss TJ, Betancourt-Solis MA, Huang HW, Lee T, McNew JA. The Atlastin C-terminal tail is an amphipathic helix that perturbs the bilayer structure during endoplasmic reticulum homotypic fusion. J Biol Chem 2015; 290:4772-4783. [PMID: 25555915 DOI: 10.1074/jbc.m114.601823] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Fusion of tubular membranes is required to form three-way junctions found in reticular subdomains of the endoplasmic reticulum. The large GTPase Atlastin has recently been shown to drive endoplasmic reticulum membrane fusion and three-way junction formation. The mechanism of Atlastin-mediated membrane fusion is distinct from SNARE-mediated membrane fusion, and many details remain unclear. In particular, the role of the amphipathic C-terminal tail of Atlastin is still unknown. We found that a peptide corresponding to the Atlastin C-terminal tail binds to membranes as a parallel α helix, induces bilayer thinning, and increases acyl chain disorder. The function of the C-terminal tail is conserved in human Atlastin. Mutations in the C-terminal tail decrease fusion activity in vitro, but not GTPase activity, and impair Atlastin function in vivo. In the context of unstable lipid bilayers, the requirement for the C-terminal tail is abrogated. These data suggest that the C-terminal tail of Atlastin locally destabilizes bilayers to facilitate membrane fusion.
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Affiliation(s)
- Joseph E Faust
- Department of Biochemistry and Cell Biology, Rice University, Houston Texas 77005
| | - Tanvi Desai
- Department of Biochemistry and Cell Biology, Rice University, Houston Texas 77005
| | - Avani Verma
- Department of Biochemistry and Cell Biology, Rice University, Houston Texas 77005
| | - Idil Ulengin
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213
| | - Tzu-Lin Sun
- Department of Physics and Astronomy, Rice University, Houston, Texas 77005
| | - Tyler J Moss
- Department of Biochemistry and Cell Biology, Rice University, Houston Texas 77005
| | | | - Huey W Huang
- Department of Physics and Astronomy, Rice University, Houston, Texas 77005
| | - Tina Lee
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213
| | - James A McNew
- Department of Biochemistry and Cell Biology, Rice University, Houston Texas 77005,.
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Leabu M, Niculite CM. Porosome: a membrane microdomain acting as the universal secretory portal in exocytosis. Discoveries (Craiova) 2014; 2:e29. [PMID: 32309556 PMCID: PMC6919544 DOI: 10.15190/d.2014.21] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2014] [Revised: 09/22/2014] [Accepted: 09/22/2014] [Indexed: 11/22/2022] Open
Abstract
Most, if not all, cells in the organism, at least in some period of their lifetime, secrete materials that are produced within the cell. Cell secretion is a phenomenon requiring membrane fusion at a specialized plasma membrane structure called the 'porosome,' which allows the material stored within secretory vesicles to be delivered to the cell's exterior environment. This is achieved when the secretory vesicles fuse at the base of the porosome complex, establishing a fusion pore or fluid continuity between the vesicle interior and the cell's exterior. Besides cell secretion, membrane fusion is necessary for intracellular membrane traffic and vesicular transport from one endomembrane bound structure to another. In addition to cell secretion, membrane fusion is necessary for intracellular membrane trafficking and vesicle transport from one intracellular membrane to another. We suggest that the debate about whether to use the term 'porosome' or 'fusion pore' to describe this process is unnecessary, since both of these terms are useful in describing aspects of the last event of cell secretion, namely exocytosis. In this review, we will summarize the information related to the discovery of the porosome, a universal secretory portal for exocytosis, and discuss porosome molecular organization and function. Finally, we will develop the notion that the porosome is a specialized plasma membrane microdomain.
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Affiliation(s)
- Mircea Leabu
- University of Medicine and Pharmacy "Carol Davila", and "Victor Babes" National Institute of Pathology, Bucharest, Romania
| | - Cristina Mariana Niculite
- University of Medicine and Pharmacy "Carol Davila", and "Victor Babes" National Institute of Pathology, Bucharest, Romania
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30
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Lobingier BT, Nickerson DP, Lo SY, Merz AJ. SM proteins Sly1 and Vps33 co-assemble with Sec17 and SNARE complexes to oppose SNARE disassembly by Sec18. eLife 2014; 3:e02272. [PMID: 24837546 PMCID: PMC4060006 DOI: 10.7554/elife.02272] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Secretory and endolysosomal fusion events are driven by SNAREs and cofactors, including Sec17/α-SNAP, Sec18/NSF, and Sec1/Munc18 (SM) proteins. SMs are essential for fusion in vivo, but the basis of this requirement is enigmatic. We now report that, in addition to their established roles as fusion accelerators, SM proteins Sly1 and Vps33 directly shield SNARE complexes from Sec17- and Sec18-mediated disassembly. In vivo, wild-type Sly1 and Vps33 function are required to withstand overproduction of Sec17. In vitro, Sly1 and Vps33 impede SNARE complex disassembly by Sec18 and ATP. Unexpectedly, Sec17 directly promotes selective loading of Sly1 and Vps33 onto cognate SNARE complexes. A large thermodynamic barrier limits SM binding, implying that significant conformational rearrangements are involved. In a working model, Sec17 and SMs accelerate fusion mediated by cognate SNARE complexes and protect them from NSF-mediated disassembly, while mis-assembled or non-cognate SNARE complexes are eliminated through kinetic proofreading by Sec18. DOI:http://dx.doi.org/10.7554/eLife.02272.001 Eukaryotic organisms, from single-celled yeast to humans, divide their cells into membrane-bound compartments (organelles) of distinct function. To move from one compartment to another, or to enter or exit a cell, large molecules like proteins are packaged into small membrane sacs called vesicles. To release its cargo, the membrane of a vesicle must fuse with the membrane of the correct destination compartment. The SNARE family of proteins plays a key role in this fusion process. As the membranes of a vesicle and target compartment come close, SNARE proteins located on each membrane form a SNARE complex that tethers the vesicle in place and causes the two membranes fuse. SNARE proteins do not act alone in this process: the SM family of proteins also plays an essential role in SNARE-mediated membrane fusion. However, it is still not clear exactly why the SM proteins are needed. Lobingier et al. used the yeast model organism and biochemical studies with purified proteins to show that SM proteins help SNARE complexes form at the right time by regulating the delicate balance between SNARE complex formation and disassembly. This is achieved through the interplay of SM proteins and two other proteins (Sec17 and Sec18). Sec17 is known to load Sec18 onto SNARE complexes to break them apart. Lobingier et al. showed that Sec17 can also load SM proteins on SNARE complexes. This hinders Sec18 action, and so helps to keep the SNARE complexes intact. Because each SM protein tested only binds to the SNARE complex that should function at the membrane where the SM protein resides, these findings suggest SM proteins perform quality control at potential sites of membrane fusion. DOI:http://dx.doi.org/10.7554/eLife.02272.002
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Affiliation(s)
- Braden T Lobingier
- Department of Biochemistry, University of Washington School of Medicine, Seattle, United States
| | - Daniel P Nickerson
- Department of Biochemistry, University of Washington School of Medicine, Seattle, United States
| | - Sheng-Ying Lo
- Department of Biochemistry, University of Washington School of Medicine, Seattle, United States
| | - Alexey J Merz
- Department of Biochemistry, University of Washington School of Medicine, Seattle, United States Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, United States
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Abstract
Lung surfactant is crucial for reducing the surface tension of alveolar space, thus preventing the alveoli from collapse. Lung surfactant is synthesized in alveolar epithelial type II cells and stored in lamellar bodies before being released via the fusion of lamellar bodies with the apical plasma membrane. SNAREs (soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptors) play an essential role in membrane fusion. We have previously demonstrated the requirement of t-SNARE (target SNARE) proteins, syntaxin 2 and SNAP-23 (N-ethylmaleimide-sensitive factor-attachment protein 23), in regulated surfactant secretion. Here, we characterized the distribution of VAMPs (vesicle-associated membrane proteins) in rat lung and alveolar type II cells. VAMP-2, -3 and -8 are shown in type II cells at both mRNA and protein levels. VAMP-2 and -8 were enriched in LB (lamellar body) fraction. Immunochemistry studies indicated that VAMP-2 was co-localized with the LB marker protein, LB-180. Functionally, the cytoplasmic domain of VAMP-2, but not VAMP-8 inhibited surfactant secretion in type II cells. We suggest that VAMP-2 is the v-SNARE (vesicle SNARE) involved in regulated surfactant secretion.
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32
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van Lengerich B, Rawle RJ, Bendix PM, Boxer SG. Individual vesicle fusion events mediated by lipid-anchored DNA. Biophys J 2014; 105:409-19. [PMID: 23870262 DOI: 10.1016/j.bpj.2013.05.056] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2012] [Revised: 05/21/2013] [Accepted: 05/29/2013] [Indexed: 11/26/2022] Open
Abstract
Membrane fusion consists of a complex rearrangement of lipids and proteins that results in the merger of two lipid bilayers. We have developed a model system that employs synthetic DNA-lipid conjugates as a surrogate for the membrane proteins involved in the biological fusion reaction. We previously showed that complementary DNA-lipids, inserted into small unilamellar vesicles, can mediate membrane fusion in bulk. Here, we use a model membrane architecture developed in our lab to directly observe single-vesicle fusion events using fluorescence microscopy. In this system, a planar tethered membrane patch serves as the target membrane for incoming vesicles. This allows us to quantify the kinetics and characteristics of individual fusion events from the perspective of the lipids or the DNA-lipids involved in the process. We find that the fusion pathways are heterogeneous, with an arrested hemi-fusion state predominating, and we quantitate the outcome and rate of fusion events to construct a mechanistic model of DNA-mediated vesicle fusion. The waiting times between docking and fusion are distributed exponentially, suggesting that fusion occurs in a single step. Our analysis indicates that when two lipid bilayers are brought into close proximity, fusion occurs spontaneously, with little or no dependence on the number of DNA hybrids formed.
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33
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Zhang Q. Imaging single synaptic vesicles in mammalian central synapses with quantum dots. Methods Mol Biol 2014; 1026:57-69. [PMID: 23749569 DOI: 10.1007/978-1-62703-468-5_5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/14/2023]
Abstract
This protocol describes a sensitive and rigorous method to monitor the movement and turnover of single synaptic vesicles in live presynaptic terminals of mammalian central nerve system. This technique makes use of fluorescent semiconductor nanocrystals, quantum dots (Qdots), by their nanometer size, superior photoproperties, and pH-sensitivity. In comparison with other fluorescent probes like styryl dyes and pH-sensitive fluorescent proteins, Qdots offer strict loading ratio, multi-modality detection, single vesicle precision, and most importantly distinctive signals for different modes of vesicle recycling. This application is spectrally compatible with existing optical labels for synapses and thus allows multichannel and simultaneous imaging. With easy modification, this technique can be applied to other types of cells.
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Affiliation(s)
- Qi Zhang
- Pharmacology Department, Vanderbilt University, Nashville, TN, USA
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34
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Peng H, Kang N, Xu J, Stanton PK, Kang J. Two distinct modes of exocytotic fusion pore expansion in large astrocytic vesicles. J Biol Chem 2013; 288:16872-16881. [PMID: 23620588 DOI: 10.1074/jbc.m113.468231] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Formation of the fusion pore is a central question for regulated exocytosis by which secretory cells release neurotransmitters or hormones. Here, by dynamically monitoring exocytosis of large vesicles (2-7 μM) in astrocytes with two-photon microscopy imaging, we found that the exocytotic fusion pore was generated from the SNARE-dependent fusion at a ring shape of the docked plasma-vesicular membrane and the movement of a fusion-produced membrane fragment. We observed two modes of fragment movements, 1) a shift fragment that shifted to expand the fusion pore and 2) a fall-in fragment that fell into the collapsed vesicle to expand the fusion pore. Shift and fall-in modes are associated with full and partial collapses of large vesicles, respectively. The astrocytic marker, sulforhodamine 101, stained the fusion-produced membrane fragment more brightly than FM 1-43. Sulforhodamine 101 imaging showed that double fusion pores could simultaneously occur in a single vesicle (16% of large vesicles) to accelerate discharge of vesicular contents. Electron microscopy of large astrocytic vesicles showed shift and fall-in membrane fragments. Two modes of fusion pore formation demonstrate a novel mechanism underlying fusion pore expansion and provide a new explanation for full and partial collapses of large secretory vesicles.
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Affiliation(s)
- Hong Peng
- Department of Cell Biology and Anatomy, New York Medical College, Valhalla, New York 10595
| | - Ning Kang
- Department of Cell Biology and Anatomy, New York Medical College, Valhalla, New York 10595
| | - Jun Xu
- East Hospital, Tongji University School of Medicine, Shanghai 200120, China.
| | - Patric K Stanton
- Department of Cell Biology and Anatomy, New York Medical College, Valhalla, New York 10595
| | - Jian Kang
- Department of Cell Biology and Anatomy, New York Medical College, Valhalla, New York 10595.
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35
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Abstract
This protocol describes a sensitive and rigorous method to monitor the movement and turnover of single synaptic vesicles in live presynaptic terminals of mammalian central nervous system. This technique makes use of Photoluminescent semiconductor nanocrystals, quantum dots (Qdots), by their nanometer size, superior photoproperties, and pH-sensitivity. In comparison with previous fluorescent probes like styryl dyes and pH-sensitive fluorescent proteins, Qdots offer strict loading ratio, multi-modality detection, single vesicle precision, and most importantly distinctive signals for different modes of vesicle fusion. Qdots are spectrally compatible with existing fluorescent probes for synaptic vesicles and thus allow multichannel -imaging. With easy modification, this technique can be applied to other types of synapses and cells.
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36
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Alabi AA, Tsien RW. Perspectives on Kiss-and-Run: Role in Exocytosis, Endocytosis, and Neurotransmission. Annu Rev Physiol 2013; 75:393-422. [DOI: 10.1146/annurev-physiol-020911-153305] [Citation(s) in RCA: 172] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- AbdulRasheed A. Alabi
- Department of Molecular and Cellular Physiology, Stanford Institute for Neuro-Innovation and Translational Neurosciences, Stanford Medical School, Stanford, California 94305;
| | - Richard W. Tsien
- Department of Physiology and Neuroscience, Center for Neural Science, NYU Neuroscience Institute, New York University, New York, NY 10016;
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37
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Diao J, Grob P, Cipriano DJ, Kyoung M, Zhang Y, Shah S, Nguyen A, Padolina M, Srivastava A, Vrljic M, Shah A, Nogales E, Chu S, Brunger AT. Synaptic proteins promote calcium-triggered fast transition from point contact to full fusion. eLife 2012; 1:e00109. [PMID: 23240085 PMCID: PMC3514886 DOI: 10.7554/elife.00109] [Citation(s) in RCA: 136] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2012] [Accepted: 09/18/2012] [Indexed: 12/18/2022] Open
Abstract
The molecular underpinnings of synaptic vesicle fusion for fast neurotransmitter release are still unclear. Here, we used a single vesicle-vesicle system with reconstituted SNARE and synaptotagmin-1 proteoliposomes to decipher the temporal sequence of membrane states upon Ca(2+)-injection at 250-500 μM on a 100-ms timescale. Furthermore, detailed membrane morphologies were imaged with cryo-electron microscopy before and after Ca(2+)-injection. We discovered a heterogeneous network of immediate and delayed fusion pathways. Remarkably, all instances of Ca(2+)-triggered immediate fusion started from a membrane-membrane point-contact and proceeded to complete fusion without discernible hemifusion intermediates. In contrast, pathways that involved a stable hemifusion diaphragm only resulted in fusion after many seconds, if at all. When complexin was included, the Ca(2+)-triggered fusion network shifted towards the immediate pathway, effectively synchronizing fusion, especially at lower Ca(2+)-concentration. Synaptic proteins may have evolved to select this immediate pathway out of a heterogeneous network of possible membrane fusion pathways.DOI:http://dx.doi.org/10.7554/eLife.00109.001.
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Affiliation(s)
- Jiajie Diao
- Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, Photon Science and Howard Hughes Medical Institute , Stanford University , Stanford , USA
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38
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Studying calcium-triggered vesicle fusion in a single vesicle-vesicle content and lipid-mixing system. Nat Protoc 2012; 8:1-16. [PMID: 23222454 PMCID: PMC3566647 DOI: 10.1038/nprot.2012.134] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
This protocol describes a single vesicle-vesicle microscopy system to study Ca(2+)-triggered vesicle fusion. Donor vesicles contain reconstituted synaptobrevin and synaptotagmin-1. Acceptor vesicles contain reconstituted syntaxin and synaptosomal-associated protein 25 (SNAP-25), and they are tethered to a PEG-coated glass surface. Donor vesicles are mixed with the tethered acceptor vesicles and incubated for several minutes at a zero-Ca(2+) concentration, resulting in a collection of single interacting vesicle pairs. The donor vesicles also contain two spectrally distinct fluorophores that allow simultaneous monitoring of temporal changes of the content and membrane. Upon Ca(2+) injection into the sample chamber, our system therefore differentiates between hemifusion and complete fusion of interacting vesicle pairs and determines the temporal sequence of these events on a sub-100-millisecond time scale. Other factors such as complexin can be easily added. Our system is unique in that it monitors both content and lipid mixing and starts from a metastable state of interacting vesicle pairs before Ca(2+) injection.
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39
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Miklavc P, Frick M. Vesicular calcium channels as regulators of the exocytotic post-fusion phase. Commun Integr Biol 2012; 4:796-8. [PMID: 22446559 DOI: 10.4161/cib.17935] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Regulated secretion is a fundamental cellular process in many different types of eukaryotic cells with Ca2(+-)triggered exocytosis taking centre stage. Elevations of the cytoplasmic Ca(2+) concentration ([Ca(2+)](c)) regulate multiple steps from vesicle fusion with the plasma membrane to fusion pore dilation and subsequent retrieval of spent vesicles. The general view is that the rise in [Ca(2+)](c) initiates during the pre-fusion stage and either results from Ca(2+)-influx via Ca(2+) channels in the plasma membrane or from release from intracellular Ca(2+)-stores. However, there is increasing evidence that exocytosis of secretory vesicles triggers additional, localised Ca(2+) signals via insertion of vesicle-associated Ca(2+) channels into the cell surface. These restricted Ca(2+) signals following fusion are ideally suited for regulating the post-fusion fate of individual secretory vesicles. In invertebrates they have been shown to trigger compensatory endocytosis. Recently we have reported that exocytosis of lamellar bodies in alveolar type II epithelial cells results in a localized Ca(2+)-influx via vesicular P2X(4) receptors which regulates fusion pore expansion and vesicle content release. This finding expands the emerging picture that post-fusion Ca(2+) entry via vesicle-associated Ca(2+) channels plays a central role for regulated exocytosis.
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Affiliation(s)
- Pika Miklavc
- Institute of General Physiology, University of Ulm, Ulm, Germany
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40
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Fischer A. Synchronized Chaperone Function of Botulinum Neurotoxin Domains Mediates Light Chain Translocation into Neurons. Curr Top Microbiol Immunol 2012. [DOI: 10.1007/978-3-662-45790-0_6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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41
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Collins R, Holz R, Zimmerberg J. 5.14 The Biophysics of Membrane Fusion. COMPREHENSIVE BIOPHYSICS 2012. [PMCID: PMC7151979 DOI: 10.1016/b978-0-12-374920-8.00523-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
A crucial interplay between protein conformations and lipid membrane energetics emerges as the guiding principle for the regulation and mechanism of membrane fusion in biological systems. As some of the basics of fusion become clear, a myriad of compelling questions come to the fore. Is the interior of the fusion pore protein or lipid? Why is synaptic release so fast? Why is PIP2 needed for exocytosis? How does fusion peptide insertion lead to fusion of viruses to cell membranes? What role does the TMD play? How can studies on membrane fission contribute to our understanding of membrane fusion? What exactly are SNARE proteins doing?
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42
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Bond LM, Brandstaetter H, Sellers JR, Kendrick-Jones J, Buss F. Myosin motor proteins are involved in the final stages of the secretory pathways. Biochem Soc Trans 2011; 39:1115-9. [PMID: 21936774 PMCID: PMC3403808 DOI: 10.1042/bst0391115] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
In eukaryotes, the final steps in both the regulated and constitutive secretory pathways can be divided into four distinct stages: (i) the 'approach' of secretory vesicles/granules to the PM (plasma membrane), (ii) the 'docking' of these vesicles/granules at the membrane itself, (iii) the 'priming' of the secretory vesicles/granules for the fusion process, and, finally, (iv) the 'fusion' of vesicular/granular membranes with the PM to permit content release from the cell. Recent work indicates that non-muscle myosin II and the unconventional myosin motor proteins in classes 1c/1e, Va and VI are specifically involved in these final stages of secretion. In the present review, we examine the roles of these myosins in these stages of the secretory pathway and the implications of their roles for an enhanced understanding of secretion in general.
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Affiliation(s)
- Lisa M. Bond
- Cambridge Institute for Medical Research, University of Cambridge, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, UK
- Laboratory of Molecular Physiology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, 20892, USA
| | - Hemma Brandstaetter
- Cambridge Institute for Medical Research, University of Cambridge, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, UK
| | - James R. Sellers
- Cambridge Institute for Medical Research, University of Cambridge, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, UK
| | | | - Folma Buss
- Cambridge Institute for Medical Research, University of Cambridge, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, UK
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43
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Wu Y, Ma L, Cheley S, Bayley H, Cui Q, Chapman ER. Permeation of styryl dyes through nanometer-scale pores in membranes. Biochemistry 2011; 50:7493-502. [PMID: 21815625 DOI: 10.1021/bi2006288] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Styryl dyes are widely used to study synaptic vesicle (SV) recycling in neurons; vesicles are loaded with dye during endocytosis, and dye is subsequently released via exocytosis. During putative kiss-and-run exocytosis, efflux of dye from individual SVs has been proposed to occur via two sequential steps: dissociation from the membrane followed by permeation through a small fusion pore. To improve our understanding of the kinetics of efflux of dye from vesicles during kiss-and-run events, we examined the rates of efflux of different dyes through nanometer-scale pores formed in membranes by the toxins melittin and α-hemolysin; these pores approximate the size of fusion pores measured in neuroendocrine cells. We found that the axial diameter of each dye was a crucial determinant for permeation. Moreover, the two dyes with the largest cross-sectional areas were completely unable to pass through pores formed by a mutant α-hemolysin that has a slightly smaller pore than the wild-type toxin. The overall time constant for efflux (seconds) of each dye was orders of magnitude slower than the time constant for dissociation from membranes (milliseconds). Thus, the permeation step is rate-limiting, and this observation was further supported by atomistic molecular dynamics simulations. Together, the data reported here help provide a framework for interpreting dye destaining rates from secretory vesicles.
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Affiliation(s)
- Yao Wu
- Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, Wisconsin 53706, United States
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44
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Fusion-activated Ca2+ entry via vesicular P2X4 receptors promotes fusion pore opening and exocytotic content release in pneumocytes. Proc Natl Acad Sci U S A 2011; 108:14503-8. [PMID: 21844344 DOI: 10.1073/pnas.1101039108] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Ca(2+) is considered a key element in multiple steps during regulated exocytosis. During the postfusion phase, an elevated cytoplasmic Ca(2+) concentration ([Ca(2+)])(c) leads to fusion pore dilation. In neurons and neuroendocrine cells, this results from activation of voltage-gated Ca(2+) channels in the plasma membrane. However, these channels are activated in the prefusion stage, and little is known about Ca(2+) entry mechanisms during the postfusion stage. This may be particularly important for slow and nonexcitable secretory cells. We recently described a "fusion-activated" Ca(2+) entry (FACE) mechanism in alveolar type II (ATII) epithelial cells. FACE follows initial fusion pore opening with a delay of 200-500 ms. The site, molecular mechanisms, and functions of this mechanism remain unknown, however. Here we show that vesicle-associated Ca(2+) channels mediate FACE. Using RT-PCR, Western blot analysis, and immunofluorescence, we demonstrate that P2X(4) receptors are expressed on exocytotic vesicles known as lamellar bodies (LBs). Electrophysiological, pharmacological, and genetic data confirm that FACE is mediated via these vesicular P2X(4) receptors. Furthermore, analysis of fluorophore diffusion into and out of individual vesicles after exocytotic fusion provides evidence that FACE regulates postfusion events of LB exocytosis via P2X(4). Fusion pore dilation was clearly correlated with the amplitude of FACE, and content release from fused LBs was accelerated in fusions followed by FACE. Based on these findings, we propose a model for regulation of the exocytotic postfusion phase in nonexcitable cells in which Ca(2+) influx via vesicular Ca(2+) channels regulates fusion pore expansion and vesicle content release.
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Ribrault C, Sekimoto K, Triller A. From the stochasticity of molecular processes to the variability of synaptic transmission. Nat Rev Neurosci 2011; 12:375-87. [PMID: 21685931 DOI: 10.1038/nrn3025] [Citation(s) in RCA: 119] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The variability of the postsynaptic response following a single action potential arises from two sources: the neurotransmitter release is probabilistic, and the postsynaptic response to neurotransmitter release has variable timing and amplitude. At individual synapses, the number of molecules of a given type that are involved in these processes is small enough that the stochastic (random) properties of molecular events cannot be neglected. How the stochasticity of molecular processes contributes to the variability of synaptic transmission, its sensitivity and its robustness to molecular fluctuations has important implications for our understanding of the mechanistic basis of synaptic transmission and of synaptic plasticity.
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Affiliation(s)
- Claire Ribrault
- Laboratoire Matières et Systèmes Complexes, CNRS-UMR7057, Université Paris 7, F-75205 Paris cedex 13, France
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Rathore SS, Ghosh N, Ouyang Y, Shen J. Topological arrangement of the intracellular membrane fusion machinery. Mol Biol Cell 2011; 22:2612-9. [PMID: 21633111 PMCID: PMC3135485 DOI: 10.1091/mbc.e11-03-0190] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The topology of the SNARE complex is strictly restricted: of all the possible topological combinations, only one is fusogenic—the topology compatible with both the basal fusion and the SM activation. A fusogenic SNARE complex must contain a complete set of the QabcR SNARE helices. Soluble N-ethylmaleimide–sensitive factor attachment protein receptors (SNAREs) form a four-helix coiled-coil bundle that juxtaposes two bilayers and drives a basal level of membrane fusion. The Sec1/Munc18 (SM) protein binds to its cognate SNARE bundle and accelerates the basal fusion reaction. The question of how the topological arrangement of the SNARE helices affects the reactivity of the fusion proteins remains unanswered. Here we address the problem for the first time in a reconstituted system containing both SNAREs and SM proteins. We find that to be fusogenic a SNARE topology must support both basal fusion and SM stimulation. Certain topological combinations of exocytic SNAREs result in basal fusion but cannot support SM stimulation, whereas other topologies support SM stimulation without inducing basal fusion. It is striking that of all the possible topological combinations of exocytic SNARE helices, only one induces efficient fusion. Our results suggest that the intracellular membrane fusion complex is designed to fuse bilayers according to one genetically programmed topology.
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Affiliation(s)
- Shailendra S Rathore
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, CO 80309, USA
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Budzinski KL, Sgro AE, Fujimoto BS, Gadd JC, Shuart NG, Gonen T, Bajjaleih SM, Chiu DT. Synaptosomes as a platform for loading nanoparticles into synaptic vesicles. ACS Chem Neurosci 2011; 2:236-241. [PMID: 21666849 DOI: 10.1021/cn200009n] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Synaptosomes are intact, isolated nerve terminals that contain the necessary machinery to recycle synaptic vesicles via endocytosis and exocytosis upon stimulation. Here we use this property of synaptosomes to load quantum dots into synaptic vesicles. Vesicles are then isolated from the synaptosomes, providing a method to probe isolated, individual synaptic vesicles where each vesicle contains a single, encapsulated nanoparticle. This technique provided an encapsulation efficiency of ~16%, that is, ~16% of the vesicles contained a single quantum dot while the remaining vesicles were empty. The ability to load single nanoparticles into synaptic vesicles opens new opportunity for employing various nanoparticle-based sensors to study the dynamics of vesicular transporters.
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Affiliation(s)
- Kristi L. Budzinski
- Department of Chemistry, ‡Department of Biochemistry Biochemistry, §Howard Hughes Medical Institute, and ∥Department of Pharmacology, University of Washington, Seattle, Washington 98195-1700, United States
| | - Allyson E. Sgro
- Department of Chemistry, ‡Department of Biochemistry Biochemistry, §Howard Hughes Medical Institute, and ∥Department of Pharmacology, University of Washington, Seattle, Washington 98195-1700, United States
| | - Bryant S. Fujimoto
- Department of Chemistry, ‡Department of Biochemistry Biochemistry, §Howard Hughes Medical Institute, and ∥Department of Pharmacology, University of Washington, Seattle, Washington 98195-1700, United States
| | - Jennifer C. Gadd
- Department of Chemistry, ‡Department of Biochemistry Biochemistry, §Howard Hughes Medical Institute, and ∥Department of Pharmacology, University of Washington, Seattle, Washington 98195-1700, United States
| | - Noah G. Shuart
- Department of Chemistry, ‡Department of Biochemistry Biochemistry, §Howard Hughes Medical Institute, and ∥Department of Pharmacology, University of Washington, Seattle, Washington 98195-1700, United States
| | - Tamir Gonen
- Department of Chemistry, ‡Department of Biochemistry Biochemistry, §Howard Hughes Medical Institute, and ∥Department of Pharmacology, University of Washington, Seattle, Washington 98195-1700, United States
| | - Sandra M. Bajjaleih
- Department of Chemistry, ‡Department of Biochemistry Biochemistry, §Howard Hughes Medical Institute, and ∥Department of Pharmacology, University of Washington, Seattle, Washington 98195-1700, United States
| | - Daniel T. Chiu
- Department of Chemistry, ‡Department of Biochemistry Biochemistry, §Howard Hughes Medical Institute, and ∥Department of Pharmacology, University of Washington, Seattle, Washington 98195-1700, United States
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Wan C, Kiessling V, Cafiso DS, Tamm LK. Partitioning of synaptotagmin I C2 domains between liquid-ordered and liquid-disordered inner leaflet lipid phases. Biochemistry 2011; 50:2478-85. [PMID: 21322640 DOI: 10.1021/bi101864k] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Synaptotagmin I is the calcium sensor in synchronous neurotransmitter release caused by fusion of synaptic vesicles with the presynaptic membrane in neurons. Synaptotagmin I interacts with acidic phospholipids, but also with soluble N-ethylmaleimide-sensitive factor attachment receptors (SNAREs), at various stages in presynaptic membrane fusion. Because SNAREs can be organized into small cholesterol-dependent clusters in membranes, it is important to determine whether the C2 domains of synaptotagmin target membrane domains with different cholesterol contents. To address this question, we used a previously developed asymmetric two-phase lipid bilayer system to investigate the membrane binding and lipid phase targeting of soluble C2A and C2AB domains of synaptotagmin. We found that both domains target more disordered cholesterol-poor domains better than highly ordered cholesterol-rich domains. The selectivity is greatest (∼3-fold) for C2A binding to disordered domains that are formed in the presence of 5 mol % PIP(2) and 15 mol % PS. It is smallest (∼1.4-fold) for C2AB binding to disordered domains that are formed in the presence of 40 mol % PS. In the course of these experiments, we also found that C2A domains in the presence of Ca(2+) and C2AB domains in the absence of Ca(2+) are quite reliable reporters of the acidic lipid distribution between ordered and disordered lipid phases. Accordingly, PS prefers the liquid-disordered phase over the liquid-ordered phase by ∼2-fold, but PIP(2) has an up to 3-fold preference for the liquid-disordered phase.
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Affiliation(s)
- Chen Wan
- Center for Membrane Biology, Department of Molecular Physiology and Biological Physics, University of Virginia, Snyder Building, P.O. Box 800886, Charlottesville, Virginia 22908, United States
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