1
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Mystek P, Singh V, Horváth M, Honzejková K, Riegerová P, Evci H, Hof M, Obšil T, Šachl R. The minimal membrane requirements for BAX-induced pore opening upon exposure to oxidative stress. Biophys J 2024:S0006-3495(24)00564-2. [PMID: 39188056 DOI: 10.1016/j.bpj.2024.08.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2024] [Revised: 07/18/2024] [Accepted: 08/22/2024] [Indexed: 08/28/2024] Open
Abstract
Perforation of the outer mitochondrial membrane triggered by BAX and facilitated by its main activator cBID is a fundamental process in cell apoptosis. Here, we employ a newly designed correlative approach based on a combination of a fluorescence cross correlation binding with a calcein permeabilization assay to understand the involvement of BAX in pore formation under oxidative stress conditions. To mimic the oxidative stress, we enriched liposomal membranes by phosphatidylcholines with truncated sn-2 acyl chains terminated by a carboxyl or aldehyde moiety. Our observations revealed that oxidative stress enhances proapoptotic conditions involving accelerated pore-opening kinetics. This enhancement is achieved through increased recruitment of BAX to the membrane and facilitation of BAX membrane insertion. Despite these effects, the fundamental mechanism of pore formation remained unchanged, suggesting an all-or-none mechanism. In line with this mechanism, we demonstrated that the minimal number of BAX molecules at the membrane necessary for pore formation remains constant regardless of BAX activation by cBID or the presence of oxidized lipids. Overall, our findings give a comprehensive picture of the molecular mechanisms underlying apoptotic pore formation and highlight the selective amplifying role of oxidized lipids in triggering formation of membrane pores.
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Affiliation(s)
- Paweł Mystek
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, Prague, Czech Republic
| | - Vandana Singh
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, Prague, Czech Republic; Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
| | - Matěj Horváth
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, Prague, Czech Republic
| | - Karolína Honzejková
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Prague, Czech Republic
| | - Petra Riegerová
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, Prague, Czech Republic
| | - Hüseyin Evci
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, Prague, Czech Republic; Department of Chemistry, Faculty of Science, University of South Bohemia in České Budějovice, České Budějovice, Czech Republic
| | - Martin Hof
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, Prague, Czech Republic
| | - Tomáš Obšil
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Prague, Czech Republic
| | - Radek Šachl
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, Prague, Czech Republic.
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2
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Nguyen D, Osterlund E, Kale J, Andrews DW. The C-terminal sequences of Bcl-2 family proteins mediate interactions that regulate cell death. Biochem J 2024; 481:903-922. [PMID: 38985308 PMCID: PMC11346437 DOI: 10.1042/bcj20210352] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2024] [Revised: 06/18/2024] [Accepted: 06/19/2024] [Indexed: 07/11/2024]
Abstract
Programmed cell death via the both intrinsic and extrinsic pathways is regulated by interactions of the Bcl-2 family protein members that determine whether the cell commits to apoptosis via mitochondrial outer membrane permeabilization (MOMP). Recently the conserved C-terminal sequences (CTSs) that mediate localization of Bcl-2 family proteins to intracellular membranes, have been shown to have additional protein-protein binding functions that contribute to the functions of these proteins in regulating MOMP. Here we review the pivotal role of CTSs in Bcl-2 family interactions including: (1) homotypic interactions between the pro-apoptotic executioner proteins that cause MOMP, (2) heterotypic interactions between pro-apoptotic and anti-apoptotic proteins that prevent MOMP, and (3) heterotypic interactions between the pro-apoptotic executioner proteins and the pro-apoptotic direct activator proteins that promote MOMP.
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Affiliation(s)
- Dang Nguyen
- Department of Medical Biophysics, Faculty of Medicine, University of Toronto, Toronto, Canada
- Biological Sciences Platform, Odette Cancer Program, Sunnybrook Research Institute, Toronto, Canada
| | - Elizabeth Osterlund
- Department of Biochemistry and Biomedical Sciences, Faculty of Health Science, McMaster University, Hamilton, Canada
| | - Justin Kale
- Biological Sciences Platform, Odette Cancer Program, Sunnybrook Research Institute, Toronto, Canada
| | - David W. Andrews
- Department of Medical Biophysics, Faculty of Medicine, University of Toronto, Toronto, Canada
- Biological Sciences Platform, Odette Cancer Program, Sunnybrook Research Institute, Toronto, Canada
- Department of Biochemistry, Faculty of Medicine, University of Toronto, Toronto, Canada
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3
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Makinwa Y, Luo Y, Musich PR, Zou Y. Canonical and Noncanonical Functions of the BH3 Domain Protein Bid in Apoptosis, Oncogenesis, Cancer Therapeutics, and Aging. Cancers (Basel) 2024; 16:2199. [PMID: 38927905 PMCID: PMC11202167 DOI: 10.3390/cancers16122199] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2024] [Revised: 06/05/2024] [Accepted: 06/09/2024] [Indexed: 06/28/2024] Open
Abstract
Effective cancer therapy with limited adverse effects is a major challenge in the medical field. This is especially complicated by the development of acquired chemoresistance. Understanding the mechanisms that underlie these processes remains a major effort in cancer research. In this review, we focus on the dual role that Bid protein plays in apoptotic cell death via the mitochondrial pathway, in oncogenesis and in cancer therapeutics. The BH3 domain in Bid and the anti-apoptotic mitochondrial proteins (Bcl-2, Bcl-XL, mitochondrial ATR) it associates with at the outer mitochondrial membrane provides us with a viable target in cancer therapy. We will discuss the roles of Bid, mitochondrial ATR, and other anti-apoptotic proteins in intrinsic apoptosis, exploring how their interaction sustains cellular viability despite the initiation of upstream death signals. The unexpected upregulation of this Bid protein in cancer cells can also be instrumental in explaining the mechanisms behind acquired chemoresistance. The stable protein associations at the mitochondria between tBid and anti-apoptotic mitochondrial ATR play a crucial role in maintaining the viability of cancer cells, suggesting a novel mechanism to induce cancer cell apoptosis by freeing tBid from the ATR associations at mitochondria.
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Affiliation(s)
- Yetunde Makinwa
- Department of Cell and Cancer Biology, University of Toledo College of Medicine and Life Sciences, Toledo, OH 43614, USA; (Y.M.); (Y.L.)
| | - Yibo Luo
- Department of Cell and Cancer Biology, University of Toledo College of Medicine and Life Sciences, Toledo, OH 43614, USA; (Y.M.); (Y.L.)
| | - Phillip R. Musich
- Department of Biomedical Sciences, Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614, USA;
| | - Yue Zou
- Department of Cell and Cancer Biology, University of Toledo College of Medicine and Life Sciences, Toledo, OH 43614, USA; (Y.M.); (Y.L.)
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4
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Yamashita G, Takano N, Kazama H, Tsukahara K, Miyazawa K. p53 regulates lysosomal membrane permeabilization as well as cytoprotective autophagy in response to DNA-damaging drugs. Cell Death Dis 2022; 8:502. [PMID: 36581628 PMCID: PMC9800408 DOI: 10.1038/s41420-022-01293-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2022] [Revised: 12/21/2022] [Accepted: 12/22/2022] [Indexed: 12/31/2022]
Abstract
Lysosomes are single-membraned organelles that mediate the intracellular degradation of macromolecules. Various stress can induce lysosomal membrane permeabilization (LMP), translocating intralysosomal components, such as cathepsins, to the cytoplasm, which induces lysosomal-dependent cell death (LDCD). This study reports that p53 regulates LMP in response to DNA-damaging drugs. Treating wild-type TP53 A549 cells with DNA-damaging drugs (namely, doxorubicin, carboplatin, and etoposide) induced LMP and accelerated cell death more rapidly than treating TP53-knockout (KO) A549 cells. This suggested p53-dependent LMP and LDCD induction in response to DNA damage. LMP was induced by p53-dependent BID upregulation and activation, followed by translocation of truncated BID to lysosomes. Simultaneously, autophagy for damaged lysosome elimination (lysophagy) was activated via the p53-mTOR-TEFB/TFE3 pathways in response to DNA damage. These data suggested the dichotomous nature of p53 for LMP regulation; LMP induction and repression via the p53-BID axis and p53-mTOR-TFEB/TFE3 pathway, respectively. Blocking autophagy with hydroxychloroquine or azithromycin as well as ATG5 KO enhanced LMP and LDCD induction after exposure to DNA-damaging drugs. Furthermore, lysosomal membrane stabilization using U18666A, a cholesterol transporter Niemann-Pick disease C1 (NPC1) inhibitor, suppressed LMP as well as LDCD in wild-type TP53, but not in TP53-KO, A549 cells. Thus, LMP is finely regulated by TP53 after exposure to DNA-damaging drugs.
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Affiliation(s)
- Gai Yamashita
- grid.412781.90000 0004 1775 2495Department of Otorhinolaryngology, Head and Neck Surgery, Tokyo Medical University Hospital, Shinjuku-ku, Tokyo, 160-0023 Japan
| | - Naoharu Takano
- grid.410793.80000 0001 0663 3325Department of Biochemistry, Tokyo Medical University, Shinjuku-ku, Tokyo, 160-8402 Japan
| | - Hiromi Kazama
- grid.410793.80000 0001 0663 3325Department of Biochemistry, Tokyo Medical University, Shinjuku-ku, Tokyo, 160-8402 Japan
| | - Kiyoaki Tsukahara
- grid.412781.90000 0004 1775 2495Department of Otorhinolaryngology, Head and Neck Surgery, Tokyo Medical University Hospital, Shinjuku-ku, Tokyo, 160-0023 Japan
| | - Keisuke Miyazawa
- grid.410793.80000 0001 0663 3325Department of Biochemistry, Tokyo Medical University, Shinjuku-ku, Tokyo, 160-8402 Japan
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5
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Calpain Inhibitors as Potential Therapeutic Modulators in Neurodegenerative Diseases. Neurochem Res 2022; 47:1125-1149. [PMID: 34982393 DOI: 10.1007/s11064-021-03521-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 12/27/2021] [Accepted: 12/28/2021] [Indexed: 02/07/2023]
Abstract
It is considered a significant challenge to understand the neuronal cell death mechanisms with a suitable cure for neurodegenerative disorders in the coming years. Calpains are one of the best-considered "cysteine proteases activated" in brain disorders. Calpain is an important marker and mediator in the pathophysiology of neurodegeneration. Calpain activation being the essential neurodegenerative factor causing apoptotic machinery activation, it is crucial to develop reliable and effective approaches to prevent calpain-mediated apoptosis in degenerating neurons. It has been recently seen that the "inhibition of calpain activation" has appeared as a possible therapeutic target for managing neurodegenerative diseases. A systematic literature review of PubMed, Medline, Bentham, Scopus, and EMBASE (Elsevier) databases was conducted. The present article reviews the basic pathobiology and role of selective calpain inhibitors used in various neurodegenerative diseases as a therapeutic target.
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6
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Rose M, Kurylowicz M, Mahmood M, Winkel S, Moran-Mirabal JM, Fradin C. Direct Measurement of the Affinity between tBid and Bax in a Mitochondria-Like Membrane. Int J Mol Sci 2021; 22:8240. [PMID: 34361006 PMCID: PMC8348223 DOI: 10.3390/ijms22158240] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2021] [Revised: 07/19/2021] [Accepted: 07/22/2021] [Indexed: 01/05/2023] Open
Abstract
The execution step in apoptosis is the permeabilization of the outer mitochondrial membrane, controlled by Bcl-2 family proteins. The physical interactions between the different proteins in this family and their relative abundance literally determine the fate of the cells. These interactions, however, are difficult to quantify, as they occur in a lipid membrane and involve proteins with multiple conformations and stoichiometries which can exist both in soluble and membrane. Here we focus on the interaction between two core Bcl-2 family members, the executor pore-forming protein Bax and the truncated form of the activator protein Bid (tBid), which we imaged at the single particle level in a mitochondria-like planar supported lipid bilayer. We inferred the conformation of the proteins from their mobility, and detected their transient interactions using a novel single particle cross-correlation analysis. We show that both tBid and Bax have at least two different conformations at the membrane, and that their affinity for one another increases by one order of magnitude (with a 2D-KD decreasing from ≃1.6μm-2 to ≃0.1μm-2) when they pass from their loosely membrane-associated to their transmembrane form. We conclude by proposing an updated molecular model for the activation of Bax by tBid.
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Affiliation(s)
- Markus Rose
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada; (M.R.); (M.K.); (M.M.); (S.W.)
| | - Martin Kurylowicz
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada; (M.R.); (M.K.); (M.M.); (S.W.)
| | - Mohammad Mahmood
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada; (M.R.); (M.K.); (M.M.); (S.W.)
| | - Sheldon Winkel
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada; (M.R.); (M.K.); (M.M.); (S.W.)
| | - Jose M. Moran-Mirabal
- Department of Chemistry and Chemical Biology, McMaster University, Hamilton, ON L8S 4M1, Canada;
| | - Cécile Fradin
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada; (M.R.); (M.K.); (M.M.); (S.W.)
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON L8S 4K1, Canada
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7
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Hung CL, Chang HH, Lee SW, Chiang YW. Stepwise activation of the pro-apoptotic protein Bid at mitochondrial membranes. Cell Death Differ 2021; 28:1910-1925. [PMID: 33462413 PMCID: PMC8184993 DOI: 10.1038/s41418-020-00716-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Revised: 12/01/2020] [Accepted: 12/16/2020] [Indexed: 01/30/2023] Open
Abstract
Caspase-8-cleaved Bid (cBid) associates with mitochondria and promotes the activation of BAX, leading to mitochondria outer membrane permeabilization (MOMP) and apoptosis. However, current structural models of cBid are largely based on studies using membrane vesicles and detergent micelles. Here we employ spin-label ESR and site-directed PEGylation methods to identify conformations of cBid at real mitochondrial membranes, revealing stepwise mechanisms in the activation process. Upon the binding of cBid to mitochondria, its structure is reorganized to expose the BH3 domain while leaving the structural integrity only slightly altered. The mitochondria-bound cBid is in association with Mtch2 and it remains in the primed state until interacting with BAX. The interaction subsequently triggers the fragmentation of cBid, causes large conformational changes, and promotes BAX-mediated MOMP. Our results reveal structural differences of cBid between mitochondria and other lipid-like environments and, moreover, highlight the role of the membrane binding in modifying cBid structure and assisting the inactive-to-active transition in function.
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Affiliation(s)
- Chien-Lun Hung
- Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan
| | - Hsin-Ho Chang
- Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan
| | - Su Wei Lee
- Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan
| | - Yun-Wei Chiang
- Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan.
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8
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Ma L, Hu S, He X, Yang N, Chen L, Yang C, Ye F, Wei T, Li M. Detection of tBid Oligomerization and Membrane Permeabilization by Graphene-Based Single-Molecule Surface-Induced Fluorescence Attenuation. NANO LETTERS 2019; 19:6937-6944. [PMID: 31558028 DOI: 10.1021/acs.nanolett.9b02223] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The permeabilization of organelle membranes by BCL-2 family proteins is a pivotal step during the regulation of apoptosis; the underlying mechanisms remain unclear. Based on the fluorescence attenuation by graphene oxide, we developed a single-molecule imaging method termed surface-induced fluorescence attenuation (smSIFA), which enabled us to track both vertical and lateral kinetics of singly labeled BCL-2 family protein tBid during membrane permeabilization. We found that tBid monomers lie shallowly on the lipid bilayer, where they self-assemble to form oligomers. During the initiation phase of self-assembly, the two central hydrophobic helices (α6 and α7) of tBid insert halfway into the phospholipid core, while the other helices remain on the surface. In oligomerized tBid clusters, α6 and α7 prefer to float up, and the other helices may sink to the bottom of the membrane and cause the formation of transient two-dimensional, micelle-like pore structures, which are responsible for the permeabilization of membranes and the induction of apoptosis. Our results shed light on the understanding of tBid-induced apoptosis, and this nanotechnology-based smSIFA approach could be used to dissect the kinetic interaction between membrane protein and lipid bilayer at the single-molecule level with subnanometer precision.
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Affiliation(s)
- Li Ma
- National Laboratory of Condensed Matter Physics and Key Laboratory of Soft Matter Physics, Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , China
- University of Chinese Academy of Sciences , Beijing 100049 , China
| | - Shuxin Hu
- National Laboratory of Condensed Matter Physics and Key Laboratory of Soft Matter Physics, Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , China
| | - Xiaolong He
- National Laboratory of Condensed Matter Physics and Key Laboratory of Soft Matter Physics, Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , China
- National Laboratory of Biomacromolecules, Institute of Biophysics , Chinese Academy of Sciences , Beijing 100101 , China
- University of Chinese Academy of Sciences , Beijing 100049 , China
| | - Na Yang
- National Laboratory of Biomacromolecules, Institute of Biophysics , Chinese Academy of Sciences , Beijing 100101 , China
- University of Chinese Academy of Sciences , Beijing 100049 , China
| | - Licui Chen
- National Laboratory of Condensed Matter Physics and Key Laboratory of Soft Matter Physics, Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , China
| | - Chenguang Yang
- National Laboratory of Condensed Matter Physics and Key Laboratory of Soft Matter Physics, Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , China
- University of Chinese Academy of Sciences , Beijing 100049 , China
| | - Fangfu Ye
- National Laboratory of Condensed Matter Physics and Key Laboratory of Soft Matter Physics, Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , China
- University of Chinese Academy of Sciences , Beijing 100049 , China
| | - Taotao Wei
- National Laboratory of Biomacromolecules, Institute of Biophysics , Chinese Academy of Sciences , Beijing 100101 , China
- University of Chinese Academy of Sciences , Beijing 100049 , China
| | - Ming Li
- National Laboratory of Condensed Matter Physics and Key Laboratory of Soft Matter Physics, Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , China
- University of Chinese Academy of Sciences , Beijing 100049 , China
- Songshan Lake Materials Laboratory , Dongguan , Guangdong 523808 , China
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9
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Unsay JD, Murad F, Hermann E, Ries J, García-Sáez AJ. Scanning Fluorescence Correlation Spectroscopy for Quantification of the Dynamics and Interactions in Tube Organelles of Living Cells. Chemphyschem 2018; 19:3273-3278. [PMID: 30335213 DOI: 10.1002/cphc.201800705] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Indexed: 01/03/2023]
Abstract
Single-molecule spectroscopic quantification of protein-protein interactions directly in the organelles of living cells is highly desirable but remains challenging. Bulk methods, such as Förster resonance energy transfer (FRET), currently only give a relative quantification of the strength of protein-protein interactions. Here, we introduce tube scanning fluorescence cross-correlation spectroscopy (tubeSFCCS) for the absolute quantification of diffusion and complex formation of fluorescently labeled molecules in the mitochondrial compartments. We determined the extent of association between the apoptosis regulators Bcl-xL and tBid at the mitochondrial outer membrane of living cells and discovered that practically all mitochondria-bound Bcl-xL and tBid are associated with each other, in contrast to undetectable association in the cytosol. Furthermore, we show further applicability of our method to other mitochondrial proteins, as well as to proteins in the endoplasmic reticulum (ER) membrane.
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Affiliation(s)
- Joseph D Unsay
- Interfaculty Institute of Biochemistry, University of Tübingen, Hoppe-Seyler-Str. 4, 72076, Tübingen, Germany
- Max Planck Insitute for Intteligen Systems, Heisenbergstrasse 3, 70569, Stuttgart, Germany
- German Cancer Research Center, Im Neuenheimer Feld 280, 62120, Heidelberg, Germany
| | - Fabronia Murad
- Interfaculty Institute of Biochemistry, University of Tübingen, Hoppe-Seyler-Str. 4, 72076, Tübingen, Germany
| | - Eduard Hermann
- Max Planck Insitute for Intteligen Systems, Heisenbergstrasse 3, 70569, Stuttgart, Germany
| | - Jonas Ries
- European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117, Heidelberg, Germany
| | - Ana J García-Sáez
- Interfaculty Institute of Biochemistry, University of Tübingen, Hoppe-Seyler-Str. 4, 72076, Tübingen, Germany
- Max Planck Insitute for Intteligen Systems, Heisenbergstrasse 3, 70569, Stuttgart, Germany
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10
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Ma ZW, Liu DX. Humanin decreases mitochondrial membrane permeability by inhibiting the membrane association and oligomerization of Bax and Bid proteins. Acta Pharmacol Sin 2018; 39:1012-1021. [PMID: 29265109 DOI: 10.1038/aps.2017.169] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2017] [Accepted: 10/18/2017] [Indexed: 12/13/2022] Open
Abstract
Humanin (HN) is a 24-residue peptide identified from the brain of a patient with Alzheimer's disease (AD). HN has been found to protect against neuronal insult caused by Aβ peptides or transfection of familial AD mutant genes. In order to elucidate the molecular mechanisms of HN neuroprotection, we explored the effects of HN on the association of Bax or Bid with lipid bilayers and their oligomerization in the membrane. By using single-molecule fluorescence and Förster resonance energy transfer techniques, we showed that Bax was mainly present as monomers, dimers and tetramers in lipid bilayers, while truncated Bid (tBid) enhanced the membrane association and tetramerization of Bax. HN (100 nmol/L) inhibited the self-association and tBid-activated association of Bax with the bilayers, and significantly decreased the proportion of Bax in tetramers. Furthermore, HN inhibited Bid translocation to lipid bilayers. HN could bind with Bax and Bid either in solution or in the membrane. However, HN could not pull the proteins out of the membrane. Based on these results, we propose that HN binds to Bax and cBid in solution and inhibits their translocation to the membrane. Meanwhile, HN interacts with the membrane-bound Bax and tBid, preventing the recruitment of cytosolic Bax and its oligomerization in the membrane. In this way, HN inhibits Bax pore formation in mitochondrial outer membrane and suppresses cytochrome c release and mitochondria-dependent apoptosis.
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11
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Ma L, Li Y, Ma J, Hu S, Li M. Watching Three-Dimensional Movements of Single Membrane Proteins in Lipid Bilayers. Biochemistry 2018; 57:4735-4740. [PMID: 29619828 DOI: 10.1021/acs.biochem.8b00253] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
It is challenging to assess protein-membrane interactions because of the lack of appropriate tools to detect position changes of single proteins in the ∼4 nm range of biological membranes. We developed an assay recently, termed surface-induced fluorescence attenuation (SIFA). It is able to track both vertical and lateral dynamic motion of singly labeled membrane proteins in supported lipid bilayers. Similar to the FRET (fluorescence resonance energy transfer) principle, SIFA takes advantage of the energy transfer from a fluorophore to a light-absorbing surface to determine the distance at 2-8 nm away from the surface. By labeling a protein with a proper fluorophore and using graphene oxide as a two-dimensional quencher, we showed that SIFA is capable of monitoring three-dimensional movements of the fluorophore-labeled protein not only inside but also above the lipid bilayer atop the graphene oxide. Our data show that SIFA is a well-suited method to study the interplay between proteins and membranes.
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Affiliation(s)
- Li Ma
- 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.,School of Physical Sciences , University of Chinese Academy of Sciences , Beijing 100049 , China
| | - Ying Li
- 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.,School of Physical Sciences , University of Chinese Academy of Sciences , Beijing 100049 , China
| | - Jianbing Ma
- 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.,School of Physical Sciences , University of Chinese Academy of Sciences , Beijing 100049 , China
| | - Shuxin Hu
- 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.,School of Physical Sciences , University of Chinese Academy of Sciences , Beijing 100049 , China
| | - Ming Li
- 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.,School of Physical Sciences , University of Chinese Academy of Sciences , Beijing 100049 , China
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12
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Hung CL, Lin YY, Chang HH, Chiang YW. Accessing local structural disruption of Bid protein during thermal denaturation by absorption-mode ESR spectroscopy. RSC Adv 2018; 8:34656-34669. [PMID: 35548640 PMCID: PMC9087001 DOI: 10.1039/c8ra06740f] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2018] [Accepted: 10/04/2018] [Indexed: 01/19/2023] Open
Abstract
The apoptotic function of Bid does not depend on its native structure.
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Affiliation(s)
- Chien-Lun Hung
- Department of Chemistry
- National Tsing Hua University
- Hsinchu 30013
- Taiwan
| | - Yu-Ying Lin
- Department of Chemistry
- National Tsing Hua University
- Hsinchu 30013
- Taiwan
| | - Hsin-Ho Chang
- Department of Chemistry
- National Tsing Hua University
- Hsinchu 30013
- Taiwan
| | - Yun-Wei Chiang
- Department of Chemistry
- National Tsing Hua University
- Hsinchu 30013
- Taiwan
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13
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Fradin C. On the importance of protein diffusion in biological systems: The example of the Bicoid morphogen gradient. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2017; 1865:1676-1686. [PMID: 28919007 DOI: 10.1016/j.bbapap.2017.09.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2017] [Revised: 08/16/2017] [Accepted: 09/05/2017] [Indexed: 10/18/2022]
Abstract
Morphogens are proteins that form concentration gradients in embryos and developing tissues, where they act as postal codes, providing cells with positional information and allowing them to behave accordingly. Bicoid was the first discovered morphogen, and remains one of the most studied. It regulates segmentation in flies, forming a striking exponential gradient along the anterior-posterior axis of early Drosophila embryos, and activating the transcription of multiple target genes in a concentration-dependent manner. In this review, the work done by us and by others to characterize the mobility of Bicoid in D. melanogaster embryos is presented. The central role played by the diffusion of Bicoid in both the establishment of the gradient and the activation of target genes is discussed, and placed in the context of the need for these processes to be all at once rapid, precise and robust. The Bicoid system, and morphogen gradients in general, remain amongst the most amazing examples of the coexistence, often observed in living systems, of small-scale disorder and large-scale spatial order. This article is part of a Special Issue entitled: Biophysics in Canada, edited by Lewis Kay, John Baenziger, Albert Berghuis and Peter Tieleman.
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Affiliation(s)
- Cécile Fradin
- Dept. of Physics and Astronomy, McMaster University, 1280 Main St W., Hamilton, ON L8S 4M1, Canada
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14
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Suhaili SH, Karimian H, Stellato M, Lee TH, Aguilar MI. Mitochondrial outer membrane permeabilization: a focus on the role of mitochondrial membrane structural organization. Biophys Rev 2017; 9:443-457. [PMID: 28823106 DOI: 10.1007/s12551-017-0308-0] [Citation(s) in RCA: 64] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Accepted: 07/31/2017] [Indexed: 12/13/2022] Open
Abstract
Apoptosis is important in regulating cell death turnover and is mediated by the intrinsic and death receptor-based extrinsic pathways which converge at the mitochondrial outer membrane (MOM) leading to mitochondrial outer membrane permeabilization (MOMP). MOMP results in the release of apoptotic proteins that further activate the downstream pathway of apoptosis. Thus, tight regulation of MOMP is crucial in controlling apoptosis, and a lack of control may lead to tissue and organ malformation and the development of cancers. Despite a growing number of studies focusing on the structure and activity of the proteins involved in mediating MOMP, such as the Bcl-2 family proteins, the mechanism of MOMP is not well understood. In particular, the crucial role of the various structural properties and changes in lipid components of the MOM in mediating the recruitment and activation of different Bcl-2 proteins remains poorly understood. Furthermore, the factors that control the changes in mitochondrial membrane integrity from the initiation to the final disruption of MOM have yet to be clearly defined. In this review, we provide an overview of studies that focus on the mitochondrial membrane with a biophysical analysis of the interactions of the Bcl-2 proteins with the mitochondrial membrane.
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Affiliation(s)
- Siti Haji Suhaili
- Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Wellington Rd, Clayton, VIC, 3800, Australia
| | - Hamed Karimian
- Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Wellington Rd, Clayton, VIC, 3800, Australia
| | - Matthew Stellato
- Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Wellington Rd, Clayton, VIC, 3800, Australia
| | - Tzong-Hsien Lee
- Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Wellington Rd, Clayton, VIC, 3800, Australia
| | - Marie-Isabel Aguilar
- Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Wellington Rd, Clayton, VIC, 3800, Australia.
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15
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Bleicken S, Hantusch A, Das KK, Frickey T, Garcia-Saez AJ. Quantitative interactome of a membrane Bcl-2 network identifies a hierarchy of complexes for apoptosis regulation. Nat Commun 2017; 8:73. [PMID: 28706229 PMCID: PMC5509671 DOI: 10.1038/s41467-017-00086-6] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2016] [Accepted: 05/31/2017] [Indexed: 11/10/2022] Open
Abstract
The Bcl-2 proteins form a complex interaction network that controls mitochondrial permeabilization and apoptosis. The relative importance of different Bcl-2 complexes and their spatio-temporal regulation is debated. Using fluorescence cross-correlation spectroscopy to quantify the interactions within a minimal Bcl-2 network, comprised by cBid, Bax, and Bcl-xL, we show that membrane insertion drastically alters the pattern of Bcl-2 complexes, and that the C-terminal helix of Bcl-xL determines its binding preferences. At physiological temperature, Bax can spontaneously activate in a self-amplifying process. Strikingly, Bax also recruits Bcl-xL to membranes, which is sufficient to retrotranslocate Bax back into solution to secure membrane integrity. Our study disentangles the hierarchy of Bcl-2 complex formation in relation to their environment: Bcl-xL association with cBid occurs in solution and in membranes, where the complex is stabilized, whereas Bcl-xL binding to Bax occurs only in membranes and with lower affinity than to cBid, leading instead to Bax retrotranslocation. The permeabilization of the mitochondrial outer membrane to induce apoptosis is regulated by complex interactions between Bcl-2 family members. Here the authors develop a quantitative interactome of a membrane Bcl-2 network and identify a hierarchy of protein complexes in apoptosis induction.
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Affiliation(s)
- Stephanie Bleicken
- Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569, Stuttgart, Germany.,German Cancer Research Center, Im Neuenheimer Feld 280, 69120, Heidelberg, Germany.,Interfaculty Institute of Biochemistry, Eberhard Karls University Tübingen, Hoppe-Seyler-Str. 4, 72076, Tübingen, Germany.,ZEMOS, Ruhr-University Bochum, Universitätsstr. 150, 44801, Bochum, Germany
| | - Annika Hantusch
- University of Konstanz, Applied Bioinformatics, Universitaetsstr. 10, 78457, Konstanz, Germany
| | - Kushal Kumar Das
- Interfaculty Institute of Biochemistry, Eberhard Karls University Tübingen, Hoppe-Seyler-Str. 4, 72076, Tübingen, Germany
| | - Tancred Frickey
- University of Konstanz, Applied Bioinformatics, Universitaetsstr. 10, 78457, Konstanz, Germany
| | - Ana J Garcia-Saez
- Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569, Stuttgart, Germany. .,German Cancer Research Center, Im Neuenheimer Feld 280, 69120, Heidelberg, Germany. .,Interfaculty Institute of Biochemistry, Eberhard Karls University Tübingen, Hoppe-Seyler-Str. 4, 72076, Tübingen, Germany.
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16
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Gahl RF, Dwivedi P, Tjandra N. Bcl-2 proteins bid and bax form a network to permeabilize the mitochondria at the onset of apoptosis. Cell Death Dis 2016; 7:e2424. [PMID: 27763642 PMCID: PMC5133987 DOI: 10.1038/cddis.2016.320] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2016] [Revised: 08/23/2016] [Accepted: 09/05/2016] [Indexed: 12/23/2022]
Abstract
The most critical step in the initiation of apoptosis is the activation of the Bcl-2 family of proteins to oligomerize and permeabilize the outer-mitochondrial membrane (OMM). As this step results in the irreversible release of factors that enhance cellular degradation, it is the point of no return in programmed cell death and would be an ideal therapeutic target. However, the arrangement of the Bcl-2 proteins in the OMM during permeabilization still remains unknown. It is also unclear whether the Bcl-2 protein, Bid, directly participates in the formation of the oligomers in live cells, even though it is cleaved and translocates to the OMM at the initiation of apoptosis. Therefore, we utilized confocal microscopy to measure Förster resonance energy transfer (FRET) efficiencies in live cells to determine the conformation(s) and intermolecular contacts of Bid within these Bcl-2 oligomers. We found that Bid adopts an extended conformation, which appears to be critical for its association with the mitochondrial membrane. This conformation is also important for intermolecular contacts within the Bid oligomer. More importantly for the first time, direct intermolecular contacts between Bid and Bax were observed, thereby, confirming Bid as a key component of these oligomers. Furthermore, the observed FRET efficiencies allowed us to propose an oligomeric arrangement of Bid, Bax, and possibly other members of the Bcl-2 family of proteins that form a self-propagating network that permeabilizes the OMM.
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Affiliation(s)
- Robert F Gahl
- Laboratory of Molecular Biophysics, Biochemistry and Biophysics Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda 20892, MD, USA
| | - Pallavi Dwivedi
- Laboratory of Molecular Biophysics, Biochemistry and Biophysics Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda 20892, MD, USA
| | - Nico Tjandra
- Laboratory of Molecular Biophysics, Biochemistry and Biophysics Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda 20892, MD, USA
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17
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Pro-apoptotic cBid and Bax exhibit distinct membrane remodeling activities: An AFM study. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1859:17-27. [PMID: 27755971 DOI: 10.1016/j.bbamem.2016.10.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Revised: 09/16/2016] [Accepted: 10/13/2016] [Indexed: 11/22/2022]
Abstract
Bcl-2 proteins are key regulators of the mitochondrial outer membrane (MOM) permeabilization that mediates apoptosis. During apoptosis, Bid is cleaved (cBid) and translocates to the MOM, where it activates Bax. Bax then oligomerizes and induces MOM permeabilization. However, little is known about how these proteins affect membrane organization aside from pore formation. In previous studies, we have shown that both cBid and Bax are able to remodel membranes and stabilize curvature. Here, we dissected the independent effects of Bax and cBid on supported lipid structures mimicking the mitochondrial composition by means of atomic force spectroscopy. We show that cBid did not permeabilize the membrane but lowered the membrane breakthrough force. On the other hand, Bax effects were dependent on its oligomeric state. Monomeric Bax did not affect the membrane properties. In contrast, oligomeric Bax lowered the breakthrough force of the membrane, which in the context of pore formation, implies a lowering of the line tension at the edge of the pore.
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18
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In situ quantification of protein binding to the plasma membrane. Biophys J 2016; 108:2648-57. [PMID: 26039166 DOI: 10.1016/j.bpj.2015.04.021] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2014] [Revised: 03/24/2015] [Accepted: 04/20/2015] [Indexed: 11/21/2022] Open
Abstract
This study presents a fluorescence-based assay that allows for direct measurement of protein binding to the plasma membrane inside living cells. An axial scan through the cell generates a fluorescence intensity profile that is analyzed to determine the membrane-bound and cytoplasmic concentrations of a peripheral membrane protein labeled by the enhanced green fluorescent protein (EGFP). The membrane binding curve is constructed by mapping those concentrations for a population of cells with a wide range of protein expression levels, and a fit of the binding curve determines the number of binding sites and the dissociation coefficient. We experimentally verified the technique, using myosin-1C-EGFP as a model system and fit its binding curve. Furthermore, we studied the protein-lipid interactions of the membrane binding domains from lactadherin and phospholipase C-δ1 to evaluate the feasibility of using competition binding experiments to identify specific lipid-protein interactions in living cells. Finally, we applied the technique to determine the lipid specificity, the number of binding sites, and the dissociation coefficient of membrane binding for the Gag matrix domain of human T-lymphotropic virus type 1, which provides insight into early assembly steps of the retrovirus.
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Rose M, Hirmiz N, Moran-Mirabal JM, Fradin C. Lipid Diffusion in Supported Lipid Bilayers: A Comparison between Line-Scanning Fluorescence Correlation Spectroscopy and Single-Particle Tracking. MEMBRANES 2015; 5:702-21. [PMID: 26610279 PMCID: PMC4704007 DOI: 10.3390/membranes5040702] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/17/2015] [Accepted: 11/06/2015] [Indexed: 11/16/2022]
Abstract
Diffusion in lipid membranes is an essential component of many cellular process and fluorescence a method of choice to study membrane dynamics. The goal of this work was to directly compare two common fluorescence methods, line-scanning fluorescence correlation spectroscopy and single-particle tracking, to observe the diffusion of a fluorescent lipophilic dye, DiD, in a complex five-component mitochondria-like solid-supported lipid bilayer. We measured diffusion coefficients of DFCS ~ 3 um2 * s-1 and DSPT ~ 2 um2 * s-1, respectively. These comparable, yet statistically different values are used to highlight the main message of the paper, namely that the two considered methods give access to distinctly different dynamic ranges: D sup or approximatively 1um2 * s-1 for FCS and D inf or approximatively 5 um2 s-1 for SPT (with standard imaging conditions). In the context of membrane diffusion, this means that FCS allows studying lipid diffusion in fluid membranes, as well as the diffusion of loosely-bound proteins hovering above the membrane. SPT, on the other hand, is ideal to study the motions of membrane-inserted proteins, especially those presenting different conformations, but only allows studying lipid diffusion in relatively viscous membranes, such as supported lipid bilayers and cell membranes.
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Affiliation(s)
- Markus Rose
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada.
| | - Nehad Hirmiz
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada.
| | - Jose M Moran-Mirabal
- Department of Chemistry and Chemical Biology, McMaster University, Hamilton, ON L8S 4L8, Canada.
| | - Cécile Fradin
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada.
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON L8N 3Z5, Canada.
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Effect of Cholesterol on the Structure of a Five-Component Mitochondria-Like Phospholipid Membrane. MEMBRANES 2015; 5:664-84. [PMID: 26529029 PMCID: PMC4704005 DOI: 10.3390/membranes5040664] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Accepted: 10/16/2015] [Indexed: 12/23/2022]
Abstract
Cellular membranes have a complex phospholipid composition that varies greatly depending on the organism, cell type and function. In spite of this complexity, most structural data available for phospholipid bilayers concern model systems containing only one or two different phospholipids. Here, we examine the effect of cholesterol on the structure of a complex membrane reflecting the lipid composition of mitochondrial membranes, with five different types of headgroups (phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylserine (PS) and cardiolipin (CL)) and a variety of hydrocarbon tails. This particular system was chosen because elevated cholesterol contents in mitochondrial membranes have been linked to a breaking down of Bax-mediated membrane permeabilization and resistance to cancer treatments. High resolution electron density profiles were determined by X-ray reflectivity, while the area per phospholipid chain, Apc, and the chain order parameter, SX-ray, were determined by wide-angle X-ray scattering (WAXS). We show that chain order increases upon the addition of cholesterol, resulting in both a thickening of the lipid bilayer and a reduction in the average surface area per phospholipid chain. This effect, well known as cholesterol’s condensation effect, is similar, but not as pronounced as for single-component phospholipid membranes. We conclude by discussing the relevance of these findings for the insertion of the pro-apoptotic protein Bax in mitochondrial membranes with elevated cholesterol content.
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21
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Distinct lipid effects on tBid and Bim activation of membrane permeabilization by pro-apoptotic Bax. Biochem J 2015; 467:495-505. [DOI: 10.1042/bj20141291] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
After exposure to stressful stimuli, apoptotic signals can be relayed to mitochondria by pro-apoptotic activator proteins, tBid (truncated Bid/p15) and Bim (Bcl-2 interacting mediator), which activate Bax (Bcl-2 associated X protein) and or Bak (Bcl-2 antagonist/killer) to induce mitochondrial outer membrane (MOM) permeabilization (MOMP). These protein–protein and protein–membrane interactions are critical for apoptosis regulation, since MOMP irreversibly leads to cell death. Whereas the distinct roles of tBid and Bim as sensors of different types of stress are well recognized, it is not known whether the molecular mechanisms whereby they initiate MOMP are the same. In the present study, we compare membrane permeabilization by Bax activated by either cBid [cleaved Bid (p7 and p15)] or Bim and we examine the role of membrane lipids in the recruitment and activation of these three Bcl-2 (B-cell lymphoma 2) pro-apoptotic proteins. We employ fluorescently-labelled proteins and liposomes to quantify the effects of specific lipids on each of the well-characterized steps in Bax-mediated membrane permeabilization. We show that high levels of cholesterol in the membrane inhibit permeabilization by categorically identifying the recruitment of Bax by the activators and Bax insertion in the membrane as the steps being hindered by cholesterol. Furthermore, we show that binding of both cBid and Bim to membranes is facilitated by electrostatic interactions with anionic phospholipids. However, whereas Bim does not require any particular anionic lipids, the conformational change in tBid depends on cardiolipin (CL). This suggests that CL can activate tBid in a similar manner to Mtch2 (mitochondrial carrier homologue 2). Thus, lipids modify multiple aspects of Bax-mediated membrane permeabilization.
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