1
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Bigman LS, Levy Y. Protein Diffusion on Charged Biopolymers: DNA versus Microtubule. Biophys J 2020; 118:3008-3018. [PMID: 32492371 DOI: 10.1016/j.bpj.2020.05.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2020] [Revised: 04/28/2020] [Accepted: 05/12/2020] [Indexed: 02/06/2023] Open
Abstract
Protein diffusion in lower-dimensional spaces is used for various cellular functions. For example, sliding on DNA is essential for proteins searching for their target sites, and protein diffusion on microtubules is important for proper cell division and neuronal development. On the one hand, these linear diffusion processes are mediated by long-range electrostatic interactions between positively charged proteins and negatively charged biopolymers and have similar characteristic diffusion coefficients. On the other hand, DNA and microtubules have different structural properties. Here, using computational approaches, we studied the mechanism of protein diffusion along DNA and microtubules by exploring the diffusion of both protein types on both biopolymers. We found that DNA-binding and microtubule-binding proteins can diffuse on each other's substrates; however, the adopted diffusion mechanism depends on the molecular properties of the diffusing proteins and the biopolymers. On the protein side, only DNA-binding proteins can perform rotation-coupled diffusion along DNA, with this being due to their higher net charge and its spatial organization at the DNA recognition helix. By contrast, the lower net charge on microtubule-binding proteins enables them to diffuse more quickly than DNA-binding proteins on both biopolymers. On the biopolymer side, microtubules possess intrinsically disordered, negatively charged C-terminal tails that interact with microtubule-binding proteins, thus supporting their diffusion. Thus, although both DNA-binding and microtubule-binding proteins can diffuse on the negatively charged biopolymers, the unique molecular features of the biopolymers and of their natural substrates are essential for function.
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Affiliation(s)
- Lavi S Bigman
- Department of Structural Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Yaakov Levy
- Department of Structural Biology, Weizmann Institute of Science, Rehovot, Israel.
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2
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Tran HT, Anderson LH, Knight JD. Membrane-Binding Cooperativity and Coinsertion by C2AB Tandem Domains of Synaptotagmins 1 and 7. Biophys J 2019; 116:1025-1036. [PMID: 30795874 DOI: 10.1016/j.bpj.2019.01.035] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Revised: 12/21/2018] [Accepted: 01/30/2019] [Indexed: 02/04/2023] Open
Abstract
Synaptotagmin-1 (Syt-1) and synaptotagmin-7 (Syt-7) contain analogous tandem C2 domains, C2A and C2B, which together sense Ca2+ to bind membranes and promote the stabilization of exocytotic fusion pores. Syt-1 triggers fast release of neurotransmitters, whereas Syt-7 functions in processes that involve lower Ca2+ concentrations such as hormone secretion. Syt-1 C2 domains are reported to bind membranes cooperatively, based on the observation that they penetrate farther into membranes as the C2AB tandem than as individual C2 domains. In contrast, we previously suggested that the two C2 domains of Syt-7 bind membranes independently, based in part on measurements of their liposome dissociation kinetics. Here, we investigated C2A-C2B interdomain cooperativity with Syt-1 and Syt-7 using directly comparable measurements. Equilibrium Ca2+ titrations demonstrate that the Syt-7 C2AB tandem binds liposomes lacking phosphatidylinositol-4,5-bisphosphate (PIP2) with greater Ca2+ sensitivity than either of its individual domains and binds to membranes containing PIP2 even in the absence of Ca2+. Stopped-flow kinetic measurements show differences in cooperativity between Syt-1 and Syt-7: Syt-1 C2AB dissociates from PIP2-free liposomes much more slowly than either of its individual C2 domains, indicating cooperativity, whereas the major population of Syt-7 C2AB has a dissociation rate comparable to its C2A domain, suggesting a lack of cooperativity. A minor subpopulation of Syt-7 C2AB dissociates at a slower rate, which could be due to a small cooperative component and/or liposome clustering. Measurements using an environment-sensitive fluorescent probe indicate that the Syt-7 C2B domain inserts deeply into membranes as part of the C2AB tandem, similar to the coinsertion previously reported for Syt-1. Overall, coinsertion of C2A and C2B domains is coupled to cooperative energetic effects in Syt-1 to a much greater extent than in Syt-7. The difference can be understood in terms of the relative contributions of C2A and C2B domains toward membrane binding in the two proteins.
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Affiliation(s)
- Hai T Tran
- Department of Chemistry, University of Colorado Denver, Denver, Colorado
| | - Lauren H Anderson
- Department of Chemistry, University of Colorado Denver, Denver, Colorado
| | - Jefferson D Knight
- Department of Chemistry, University of Colorado Denver, Denver, Colorado.
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3
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Brander S, Jank T, Hugel T. AFM Imaging Suggests Receptor-Free Penetration of Lipid Bilayers by Toxins. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:365-371. [PMID: 30565941 DOI: 10.1021/acs.langmuir.8b03146] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
A crucial step of exotoxin action is the attack on the membrane. Many exotoxins show an architecture following the AB model, where a binding subunit translocates an "action" subunit across a cell membrane. Atomic force microscopy is an ideal technique to study these systems because of its ability to provide structural as well as dynamic information at the same time. We report first images of toxins Photorhabdus luminescens TcdA1 and Clostridium difficile TcdB on a supported lipid bilayer. A significant amount of toxin binds to the bilayer at neutral pH in the absence of receptors. Lack of diffusion indicates that toxin particles penetrate the membrane. This observation is supported by fluorescence recovery after photobleaching measurements. We mimic endocytosis by acidification while imaging the particles over time; however, we see no large conformational change. We therefore conclude that the toxin particles we imaged in neutral conditions had already formed a pore and speculate that there is no "pre-pore" state in our imaging conditions (i.e., in the absence of receptor).
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4
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Cholesterol promotes Cytolysin A activity by stabilizing the intermediates during pore formation. Proc Natl Acad Sci U S A 2018; 115:E7323-E7330. [PMID: 30012608 DOI: 10.1073/pnas.1721228115] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Pore-forming toxins (PFTs) form nanoscale pores across target membranes causing cell death. Cytolysin A (ClyA) from Escherichia coli is a prototypical α-helical toxin that contributes to cytolytic phenotype of several pathogenic strains. It is produced as a monomer and, upon membrane exposure, undergoes conformational changes and finally oligomerizes to form a dodecameric pore, thereby causing ion imbalance and finally cell death. However, our current understanding of this assembly process is limited to studies in detergents, which do not capture the physicochemical properties of biological membranes. Here, using single-molecule imaging and molecular dynamics simulations, we study the ClyA assembly pathway on phospholipid bilayers. We report that cholesterol stimulates pore formation, not by enhancing initial ClyA binding to the membrane but by selectively stabilizing a protomer-like conformation. This was mediated by specific interactions by cholesterol-interacting residues in the N-terminal helix. Additionally, cholesterol stabilized the oligomeric structure using bridging interactions in the protomer-protomer interfaces, thereby resulting in enhanced ClyA oligomerization. This dual stabilization of distinct intermediates by cholesterol suggests a possible molecular mechanism by which ClyA achieves selective membrane rupture of eukaryotic cell membranes. Topological similarity to eukaryotic membrane proteins suggests evolution of a bacterial α-toxin to adopt eukaryotic motifs for its activation. Broad mechanistic correspondence between pore-forming toxins hints at a wider prevalence of similar protein membrane insertion mechanisms.
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MacDougall DD, Lin Z, Chon NL, Jackman SL, Lin H, Knight JD, Anantharam A. The high-affinity calcium sensor synaptotagmin-7 serves multiple roles in regulated exocytosis. J Gen Physiol 2018; 150:783-807. [PMID: 29794152 PMCID: PMC5987875 DOI: 10.1085/jgp.201711944] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Accepted: 05/07/2018] [Indexed: 12/19/2022] Open
Abstract
MacDougall et al. review the structure and function of the calcium sensor synaptotagmin-7 in exocytosis. Synaptotagmin (Syt) proteins comprise a 17-member family, many of which trigger exocytosis in response to calcium. Historically, most studies have focused on the isoform Syt-1, which serves as the primary calcium sensor in synchronous neurotransmitter release. Recently, Syt-7 has become a topic of broad interest because of its extreme calcium sensitivity and diversity of roles in a wide range of cell types. Here, we review the known and emerging roles of Syt-7 in various contexts and stress the importance of its actions. Unique functions of Syt-7 are discussed in light of recent imaging, electrophysiological, and computational studies. Particular emphasis is placed on Syt-7–dependent regulation of synaptic transmission and neuroendocrine cell secretion. Finally, based on biochemical and structural data, we propose a mechanism to link Syt-7’s role in membrane fusion with its role in subsequent fusion pore expansion via strong calcium-dependent phospholipid binding.
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Affiliation(s)
| | - Zesen Lin
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| | - Nara L Chon
- Department of Chemistry, University of Colorado, Denver, CO
| | - Skyler L Jackman
- Vollum Institute, Oregon Health & Science University, Portland, OR
| | - Hai Lin
- Department of Chemistry, University of Colorado, Denver, CO
| | | | - Arun Anantharam
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
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Ma L, Cai Y, Li Y, Jiao J, Wu Z, O'Shaughnessy B, De Camilli P, Karatekin E, Zhang Y. Single-molecule force spectroscopy of protein-membrane interactions. eLife 2017; 6:30493. [PMID: 29083305 PMCID: PMC5690283 DOI: 10.7554/elife.30493] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Accepted: 10/29/2017] [Indexed: 12/17/2022] Open
Abstract
Many biological processes rely on protein–membrane interactions in the presence of mechanical forces, yet high resolution methods to quantify such interactions are lacking. Here, we describe a single-molecule force spectroscopy approach to quantify membrane binding of C2 domains in Synaptotagmin-1 (Syt1) and Extended Synaptotagmin-2 (E-Syt2). Syts and E-Syts bind the plasma membrane via multiple C2 domains, bridging the plasma membrane with synaptic vesicles or endoplasmic reticulum to regulate membrane fusion or lipid exchange, respectively. In our approach, single proteins attached to membranes supported on silica beads are pulled by optical tweezers, allowing membrane binding and unbinding transitions to be measured with unprecedented spatiotemporal resolution. C2 domains from either protein resisted unbinding forces of 2–7 pN and had binding energies of 4–14 kBT per C2 domain. Regulation by bilayer composition or Ca2+ recapitulated known properties of both proteins. The method can be widely applied to study protein–membrane interactions.
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Affiliation(s)
- Lu Ma
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States.,CAS Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.,Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China
| | - Yiying Cai
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States.,Department of Neuroscience, Yale University School of Medicine, New Haven, United States.,Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, United States.,Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, United States
| | - Yanghui Li
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States.,College of Optical and Electronic Technology, China Jiliang University, Hangzhou, China
| | - Junyi Jiao
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States.,Integrated Graduate Program in Physical and Engineering Biology, Yale University, New Haven, United States
| | - Zhenyong Wu
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, United States.,Nanobiology Institute, Yale University, West Haven, United States
| | - Ben O'Shaughnessy
- Department of Chemical Engineering, Columbia University, New York, United States
| | - Pietro De Camilli
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States.,Department of Neuroscience, Yale University School of Medicine, New Haven, United States.,Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, United States.,Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, United States.,Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, United States
| | - Erdem Karatekin
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, United States.,Nanobiology Institute, Yale University, West Haven, United States.,Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, United States.,Laboratoire de Neurophotonique, Faculté des Sciences Fondamentales et Biomédicales, Centre National de la Recherche Scientifique (CNRS) UMR 8250, Université Paris Descartes, Paris, France
| | - Yongli Zhang
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States
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Yamamoto E. Computational and theoretical approaches for studies of a lipid recognition protein on biological membranes. Biophys Physicobiol 2017; 14:153-160. [PMID: 29159013 PMCID: PMC5689545 DOI: 10.2142/biophysico.14.0_153] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Accepted: 09/26/2017] [Indexed: 01/13/2023] Open
Abstract
Many cellular functions, including cell signaling and related events, are regulated by the association of peripheral membrane proteins (PMPs) with biological membranes containing anionic lipids, e.g., phosphatidylinositol phosphate (PIP). This association is often mediated by lipid recognition modules present in many PMPs. Here, I summarize computational and theoretical approaches to investigate the molecular details of the interactions and dynamics of a lipid recognition module, the pleckstrin homology (PH) domain, on biological membranes. Multiscale molecular dynamics simulations using combinations of atomistic and coarse-grained models yielded results comparable to those of actual experiments and could be used to elucidate the molecular mechanisms of the formation of protein/lipid complexes on membrane surfaces, which are often difficult to obtain using experimental techniques. Simulations revealed some modes of membrane localization and interactions of PH domains with membranes in addition to the canonical binding mode. In the last part of this review, I address the dynamics of PH domains on the membrane surface. Local PIP clusters formed around the proteins exhibit anomalous fluctuations. This dynamic change in protein-lipid interactions cause temporally fluctuating diffusivity of proteins, i.e., the short-term diffusivity of the bound protein changes substantially with time, and may in turn contribute to the formation/dissolution of protein complexes in membranes.
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Affiliation(s)
- Eiji Yamamoto
- Graduate School of Science and Technology, Keio University, Yokohama, Kanagawa 223-8522, Japan
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8
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Xiao B, Li J, Fan Y, Ye M, Lv S, Xu B, Chai Y, Zhou Z, Wu M, Zhu X. Downregulation of SYT7 inhibits glioblastoma growth by promoting cellular apoptosis. Mol Med Rep 2017; 16:9017-9022. [PMID: 28990113 DOI: 10.3892/mmr.2017.7723] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Accepted: 08/17/2017] [Indexed: 11/06/2022] Open
Abstract
Synaptotagmin‑7 (SYT7) is a member of the synaptotagmin gene family, and encodes a protein that mediates the calcium‑dependent regulation of membrane trafficking during synaptic transmission. A previous study demonstrated that the expression of SYT7 is associated with prostate cancer and serves an important role in development of prostate cancer. However, the roles of SYT7 in the progression of glioma remain unknown. In the present study, reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) analysis demonstrated that SYT7 was expressed in three human glioma cell lines. Western blotting and RT‑qPCR analysis demonstrated the knockdown efficiency of SYT7 shRNA in 293T cells and U87MG cells. Celigo Image Cytometer Analysis, a caspase‑3/7 assay, flow cytometry and an MTT assay demonstrated that the proliferation of U87MG cells was inhibited as SYT7 was downregulated by a lentiviral vector expressing SYT7 shRNA, via the promotion of cellular apoptosis. The results of the present study demonstrated that the downregulation of SYT7 inhibited glioblastoma growth by promoting cellular apoptosis, and that SYT7 may therefore be a potential target for glioma intervention.
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Affiliation(s)
- Bing Xiao
- Department of Neurosurgery, The Second Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Jianbin Li
- Department of Neurosurgery, The Second Hospital of Nanchang, Nanchang, Jiangxi 330003, P.R. China
| | - Yanghua Fan
- Department of Neurosurgery, The Second Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Minhua Ye
- Department of Neurosurgery, The Second Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Shigang Lv
- Department of Neurosurgery, The Second Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Bin Xu
- Department of Neurosurgery, The Second Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Yi Chai
- Department of Neurosurgery, The Second Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Zhiqing Zhou
- Department of Oncology, The Second People's Hospital of Huaihua City, Huaihua, Hunan 418000, P.R. China
| | - Miaojing Wu
- Department of Neurosurgery, The Second Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Xingen Zhu
- Department of Neurosurgery, The Second Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, P.R. China
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9
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Kiessling V, Liang B, Kreutzberger AJB, Tamm LK. Planar Supported Membranes with Mobile SNARE Proteins and Quantitative Fluorescence Microscopy Assays to Study Synaptic Vesicle Fusion. Front Mol Neurosci 2017; 10:72. [PMID: 28360838 PMCID: PMC5352703 DOI: 10.3389/fnmol.2017.00072] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Accepted: 03/03/2017] [Indexed: 12/31/2022] Open
Abstract
Synaptic vesicle membrane fusion, the process by which neurotransmitter gets released at the presynaptic membrane is mediated by a complex interplay between proteins and lipids. The realization that the lipid bilayer is not just a passive environment where other molecular players like SNARE proteins act, but is itself actively involved in the process, makes the development of biochemical and biophysical assays particularly challenging. We summarize in vitro assays that use planar supported membranes and fluorescence microscopy to address some of the open questions regarding the molecular mechanisms of SNARE-mediated membrane fusion. Most of the assays discussed in this mini-review were developed in our lab over the last 15 years. We emphasize the sample requirements that we found are important for the successful application of these methods.
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Affiliation(s)
- Volker Kiessling
- Center for Membrane and Cell Physiology, University of VirginiaCharlottesville, VA, USA; Department of Molecular Physiology and Biological Physics, University of VirginiaCharlottesville, VA, USA
| | - Binyong Liang
- Center for Membrane and Cell Physiology, University of VirginiaCharlottesville, VA, USA; Department of Molecular Physiology and Biological Physics, University of VirginiaCharlottesville, VA, USA
| | - Alex J B Kreutzberger
- Center for Membrane and Cell Physiology, University of VirginiaCharlottesville, VA, USA; Department of Molecular Physiology and Biological Physics, University of VirginiaCharlottesville, VA, USA
| | - Lukas K Tamm
- Center for Membrane and Cell Physiology, University of VirginiaCharlottesville, VA, USA; Department of Molecular Physiology and Biological Physics, University of VirginiaCharlottesville, VA, USA
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10
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Vermaas JV, Tajkhorshid E. Differential Membrane Binding Mechanics of Synaptotagmin Isoforms Observed in Atomic Detail. Biochemistry 2016; 56:281-293. [PMID: 27997124 DOI: 10.1021/acs.biochem.6b00468] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Synaptotagmin (Syt) is a membrane-associated protein involved in vesicle fusion through the SNARE complex that is found throughout the human body in 17 different isoforms. These isoforms have two membrane-binding C2 domains, which sense Ca2+ and thereby promote anionic membrane binding and lead to vesicle fusion. Through molecular dynamics simulations using the highly mobile membrane mimetic acclerated bilayer model, we have investigated how small protein sequence changes in the Ca2+-binding loops of the C2 domains may give rise to the experimentally determined difference in binding kinetics between Syt-1 and Syt-7 isoforms. Syt-7 C2 domains are found to form more close contacts with anionic phospholipid headgroups, particularly in loop 1, where an additional positive charge in Syt-7 draws the loop closer to the membrane and causes the anchoring residue F167 to insert deeper into the bilayer than the corresponding methionine in Syt-1 (M173). By performing additional replica exchange umbrella sampling calculations, we demonstrate that these additional contacts increase the energetic cost of unbinding the Syt-7 C2 domains from the bilayer, causing them to unbind more slowly than their counterparts in Syt-1.
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Affiliation(s)
- Josh V Vermaas
- Center for Biophysics and Quantitative Biology, Department of Biochemistry, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Emad Tajkhorshid
- Center for Biophysics and Quantitative Biology, Department of Biochemistry, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
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11
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Chon NL, Osterberg JR, Henderson J, Khan HM, Reuter N, Knight JD, Lin H. Membrane Docking of the Synaptotagmin 7 C2A Domain: Computation Reveals Interplay between Electrostatic and Hydrophobic Contributions. Biochemistry 2015; 54:5696-711. [DOI: 10.1021/acs.biochem.5b00422] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- Nara Lee Chon
- Department
of Chemistry, University of Colorado Denver, Denver, Colorado 80217-3364, United States
| | - J. Ryan Osterberg
- Department
of Chemistry, University of Colorado Denver, Denver, Colorado 80217-3364, United States
| | - Jack Henderson
- Department
of Chemistry, University of Colorado Denver, Denver, Colorado 80217-3364, United States
| | - Hanif M. Khan
- Department
of Molecular Biology, University of Bergen, 5008 Bergen, Norway
- Computational
Biology Unit, Department of Informatics, University of Bergen, 5008 Bergen, Norway
| | - Nathalie Reuter
- Department
of Molecular Biology, University of Bergen, 5008 Bergen, Norway
- Computational
Biology Unit, Department of Informatics, University of Bergen, 5008 Bergen, Norway
| | - Jefferson D. Knight
- Department
of Chemistry, University of Colorado Denver, Denver, Colorado 80217-3364, United States
| | - Hai Lin
- Department
of Chemistry, University of Colorado Denver, Denver, Colorado 80217-3364, United States
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