1
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Posey AE, Ross KA, Bagheri M, Lanum EN, Khan MA, Jennings CE, Harwig MC, Kennedy NW, Hilser VJ, Harden JL, Hill RB. The variable domain from dynamin-related protein 1 promotes liquid-liquid phase separation that enhances its interaction with cardiolipin-containing membranes. Protein Sci 2023; 32:e4787. [PMID: 37743569 PMCID: PMC10578129 DOI: 10.1002/pro.4787] [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: 06/12/2023] [Revised: 09/19/2023] [Accepted: 09/20/2023] [Indexed: 09/26/2023]
Abstract
Dynamins are an essential superfamily of mechanoenzymes that remodel membranes and often contain a "variable domain" important for regulation. For the mitochondrial fission dynamin, dynamin-related protein 1, a regulatory role for the variable domain (VD) is demonstrated by gain- and loss-of-function mutations, yet the basis for this is unclear. Here, the isolated VD is shown to be intrinsically disordered and undergo a cooperative transition in the stabilizing osmolyte trimethylamine N-oxide. However, the osmolyte-induced state is not folded and surprisingly appears as a condensed state. Other co-solutes including known molecular crowder Ficoll PM 70, also induce a condensed state. Fluorescence recovery after photobleaching experiments reveal this state to be liquid-like indicating the VD undergoes a liquid-liquid phase separation under crowding conditions. These crowding conditions also enhance binding to cardiolipin, a mitochondrial lipid, which appears to promote phase separation. Since dynamin-related protein 1 is found assembled into discrete punctate structures on the mitochondrial surface, the inference from the present work is that these structures might arise from a condensed state involving the VD that may enable rapid tuning of mechanoenzyme assembly necessary for fission.
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Affiliation(s)
- Ammon E. Posey
- Program in Molecular BiophysicsJohns Hopkins UniversityBaltimoreMarylandUSA
- Present address:
Department of Biomedical EngineeringWashington UniversitySt. LouisMissouriUSA
| | - Kyle A. Ross
- Department of BiochemistryMedical College of WisconsinMilwaukeeWisconsinUSA
| | - Mehran Bagheri
- Department of PhysicsUniversity of OttawaOttawaOntarioUSA
| | - Elizabeth N. Lanum
- Department of BiochemistryMedical College of WisconsinMilwaukeeWisconsinUSA
| | - Misha A. Khan
- Department of BiochemistryMedical College of WisconsinMilwaukeeWisconsinUSA
| | | | - Megan C. Harwig
- Department of BiochemistryMedical College of WisconsinMilwaukeeWisconsinUSA
| | - Nolan W. Kennedy
- Department of BiochemistryMedical College of WisconsinMilwaukeeWisconsinUSA
| | - Vincent J. Hilser
- Program in Molecular BiophysicsJohns Hopkins UniversityBaltimoreMarylandUSA
| | | | - R. Blake Hill
- Department of BiochemistryMedical College of WisconsinMilwaukeeWisconsinUSA
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2
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Soond SM, Savvateeva LV, Makarov VA, Gorokhovets NV, Townsend PA, Zamyatnin AA. Cathepsin S Cleaves BAX as a Novel and Therapeutically Important Regulatory Mechanism for Apoptosis. Pharmaceutics 2021; 13:pharmaceutics13030339. [PMID: 33807987 PMCID: PMC8035670 DOI: 10.3390/pharmaceutics13030339] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2021] [Revised: 02/08/2021] [Accepted: 03/01/2021] [Indexed: 12/11/2022] Open
Abstract
Certain lysosomal cathepsin proteins have come into focus as being good candidates for therapeutic targeting, based on them being over-expressed in a variety of cancers and based on their regulation of the apoptotic pathway. Here, we report novel findings that highlight the ability of cathepsin S expression to be up-regulated under Paclitaxel-stimulatory conditions in kidney cell lines and it being able to cleave the apoptotic p21 BAX protein in intact cells and in vitro. Consistent with this, we demonstrate that this effect can be abrogated in vitro and in mammalian cells under conditions that utilize dominant-inhibitory cathepsin S expression, cathepsin S expression-knockdown and through the activity of a novel peptide inhibitor, CS-PEP1. Moreover, we report a unique role for cathepsin S in that it can cleave a polyubiquitinated-BAX protein intermediate and is a step that may contribute to down-regulating post-translationally-modified levels of BAX protein. Finally, CS-PEP1 may possess promising activity as a potential anti-cancer therapeutic against chemotherapeutic-resistant Renal Clear Cell Carcinoma kidney cancer cells and for combined uses with therapeutics such as Paclitaxel.
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Affiliation(s)
- Surinder M. Soond
- Institute of Molecular Medicine, Sechenov First Moscow State Medical University, Trubetskaya Str. 8-2, 119991 Moscow, Russia; (L.V.S.); (V.A.M.); (N.V.G.)
- Correspondence: (S.M.S.); (A.A.Z.J.)
| | - Lyudmila V. Savvateeva
- Institute of Molecular Medicine, Sechenov First Moscow State Medical University, Trubetskaya Str. 8-2, 119991 Moscow, Russia; (L.V.S.); (V.A.M.); (N.V.G.)
| | - Vladimir A. Makarov
- Institute of Molecular Medicine, Sechenov First Moscow State Medical University, Trubetskaya Str. 8-2, 119991 Moscow, Russia; (L.V.S.); (V.A.M.); (N.V.G.)
| | - Neonila V. Gorokhovets
- Institute of Molecular Medicine, Sechenov First Moscow State Medical University, Trubetskaya Str. 8-2, 119991 Moscow, Russia; (L.V.S.); (V.A.M.); (N.V.G.)
| | - Paul A. Townsend
- Division of Cancer Sciences and Manchester Cancer Research Centre, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PL, UK;
- Faculty of Health and Medical Sciences, University of Surrey, Guildford, Surrey GU2 7X, UK
| | - Andrey A. Zamyatnin
- Institute of Molecular Medicine, Sechenov First Moscow State Medical University, Trubetskaya Str. 8-2, 119991 Moscow, Russia; (L.V.S.); (V.A.M.); (N.V.G.)
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia
- Department of Biotechnology, Sirius University of Science and Technology, 1 Olympic Ave, 354340 Sochi, Russia
- Correspondence: (S.M.S.); (A.A.Z.J.)
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3
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Campbell ST, Carlson KJ, Buchholz CJ, Helmers MR, Ghosh I. Mapping the BH3 Binding Interface of Bcl-xL, Bcl-2, and Mcl-1 Using Split-Luciferase Reassembly. Biochemistry 2015; 54:2632-43. [PMID: 25844633 DOI: 10.1021/bi501505y] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The recognition of helical BH3 domains by Bcl-2 homology (BH) receptors plays a central role in apoptosis. The residues that determine specificity or promiscuity in this interactome are difficult to predict from structural and computational data. Using a cell free split-luciferase system, we have generated a 276 pairwise interaction map for 12 alanine mutations at the binding interface for three receptors, Bcl-xL, Bcl-2, and Mcl-1, and interrogated them against BH3 helices derived from Bad, Bak, Bid, Bik, Bim, Bmf, Hrk, and Puma. This panel, in conjunction with previous structural and functional studies, starts to provide a more comprehensive portrait of this interactome, explains promiscuity, and uncovers surprising details; for example, the Bcl-xL R139A mutation disrupts binding to all helices but the Bad-BH3 peptide, and Mcl-1 binding is particularly perturbed by only four mutations of the 12 tested (V220A, N260A, R263A, and F319A), while Bcl-xL and Bcl-2 have a more diverse set of important residues depending on the bound helix.
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Affiliation(s)
- Sean T Campbell
- Department of Chemistry and Biochemistry, University of Arizona, 1306 East University Boulevard, Tucson, Arizona 85721, United States
| | - Kevin J Carlson
- Department of Chemistry and Biochemistry, University of Arizona, 1306 East University Boulevard, Tucson, Arizona 85721, United States
| | - Carl J Buchholz
- Department of Chemistry and Biochemistry, University of Arizona, 1306 East University Boulevard, Tucson, Arizona 85721, United States
| | - Mark R Helmers
- Department of Chemistry and Biochemistry, University of Arizona, 1306 East University Boulevard, Tucson, Arizona 85721, United States
| | - Indraneel Ghosh
- Department of Chemistry and Biochemistry, University of Arizona, 1306 East University Boulevard, Tucson, Arizona 85721, United States
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4
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Peter B, Polyansky AA, Fanucchi S, Dirr HW. A Lys-Trp cation-π interaction mediates the dimerization and function of the chloride intracellular channel protein 1 transmembrane domain. Biochemistry 2013; 53:57-67. [PMID: 24328417 DOI: 10.1021/bi401433f] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Chloride intracellular channel protein 1 (CLIC1) is a dual-state protein that can exist either as a soluble monomer or in an integral membrane form. The oligomerization of the transmembrane domain (TMD) remains speculative despite it being implicated in pore formation. The extent to which electrostatic and van der Waals interactions drive folding and association of the dimorphic TMD is unknown and is complicated by the requirement of interactions favorable in both aqueous and membrane environments. Here we report a putative Lys37-Trp35 cation-π interaction and show that it stabilizes the dimeric form of the CLIC1 TMD in membranes. A synthetic 30-mer peptide comprising a K37M TMD mutant was examined in 2,2,2-trifluoroethanol, sodium dodecyl sulfate micelles, and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine liposomes using far-ultraviolet (UV) circular dichroism, fluorescence, and UV absorbance spectroscopy. Our data suggest that Lys37 is not implicated in the folding, stability, or membrane insertion of the TMD peptide. However, removal of this residue impairs the formation of dimers and higher-order oligomers. This is accompanied by a 30-fold loss of chloride influx activity, suggesting that dimerization modulates the rate of chloride conductance. We propose that, within membranes, individual TMD helices associate via a Lys37-mediated cation-π interaction to form active dimers. The latter findings are also supported by results of modeling a putative TMD dimer conformation in which Lys37 and Trp35 form cation-π pairs at the dimer interface. Dimeric helix bundles may then associate to form fully active ion channels. Thus, within a membrane-like environment, aromatic interactions involving a polar lysine side chain provide a thermodynamic driving force for helix-helix association.
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Affiliation(s)
- Bradley Peter
- Protein Structure-Function Research Unit, School of Molecular and Cell Biology, University of the Witwatersrand , Johannesburg 2050, South Africa
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5
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Vargas-Uribe M, Rodnin MV, Ladokhin AS. Comparison of membrane insertion pathways of the apoptotic regulator Bcl-xL and the diphtheria toxin translocation domain. Biochemistry 2013; 52:7901-9. [PMID: 24134052 DOI: 10.1021/bi400926k] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The diphtheria toxin translocation domain (T-domain) and the apoptotic repressor Bcl-xL are membrane proteins that adopt their final topology by switching folds from a water-soluble to a membrane-inserted state. While the exact molecular mechanisms of this transition are not clearly understood in either case, the similarity in the structures of soluble states of the T-domain and Bcl-xL led to the suggestion that their membrane insertion pathways will be similar, as well. Previously, we have applied an array of spectroscopic methods to characterize the pH-triggered refolding and membrane insertion of the diphtheria toxin T-domain. Here, we use the same set of methods to describe the membrane insertion pathway of Bcl-xL, which allows us to make a direct comparison between both systems with respect to the thermodynamic stability in solution, pH-dependent membrane association, and transmembrane insertion. Thermal denaturation measured by circular dichroism indicates that, unlike the T-domain, Bcl-xL does not undergo a pH-dependent destabilization of the structure. Förster resonance energy transfer measurements demonstrate that Bcl-xL undergoes reversible membrane association modulated by the presence of anionic lipids, suggesting that formation of the membrane-competent form occurs close to the membrane interface. Membrane insertion of the main hydrophobic helical hairpin of Bcl-xL, α5-α6, was studied by site-selective attachment of environment-sensitive dye NBD. In contrast to the insertion of the corresponding TH8-TH9 hairpin into the T-domain, insertion of α5-α6 was found not to depend strongly on the presence of anionic lipids. Taken together, our results indicate that while Bcl-xL and the T-domain share structural similarities, their modes of conformational switching and membrane insertion pathways are distinctly different.
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Affiliation(s)
- Mauricio Vargas-Uribe
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center , Kansas City, Kansas 66160, United States
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6
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Peter B, Ngubane NCML, Fanucchi S, Dirr HW. Membrane Mimetics Induce Helix Formation and Oligomerization of the Chloride Intracellular Channel Protein 1 Transmembrane Domain. Biochemistry 2013; 52:2739-49. [DOI: 10.1021/bi4002776] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- Bradley Peter
- Protein Structure-Function Research
Unit, School of
Molecular and Cell Biology, University of the Witwatersrand, Johannesburg 2050, South Africa
| | - Nomxolisi Chloë Mina-Liz Ngubane
- Protein Structure-Function Research
Unit, School of
Molecular and Cell Biology, University of the Witwatersrand, Johannesburg 2050, South Africa
| | - Sylvia Fanucchi
- Protein Structure-Function Research
Unit, School of
Molecular and Cell Biology, University of the Witwatersrand, Johannesburg 2050, South Africa
| | - Heini W. Dirr
- Protein Structure-Function Research
Unit, School of
Molecular and Cell Biology, University of the Witwatersrand, Johannesburg 2050, South Africa
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7
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Rosas-Trigueros JL, Correa-Basurto J, Benítez-Cardoza CG, Zamorano-Carrillo A. Insights into the structural stability of Bax from molecular dynamics simulations at high temperatures. Protein Sci 2011; 20:2035-46. [PMID: 21936009 DOI: 10.1002/pro.740] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2011] [Revised: 09/05/2011] [Accepted: 09/08/2011] [Indexed: 01/05/2023]
Abstract
Bax is a member of the Bcl-2 protein family that participates in mitochondrion-mediated apoptosis. In the early stages of the apoptotic pathway, this protein migrates from the cytosol to the outer mitochondrial membrane, where it is inserted and usually oligomerizes, making cytochrome c-compatible pores. Although several cellular and structural studies have been reported, a description of the stability of Bax at the molecular level remains elusive. This article reports molecular dynamics simulations of monomeric Bax at 300, 400, and 500 K, focusing on the most relevant structural changes and relating them to biological experimental results. Bax gradually loses its α-helices when it is submitted to high temperatures, yet it maintains its globular conformation. The resistance of Bax to adopt an extended conformation could be due to several interactions that were found to be responsible for maintaining the structural stability of this protein. Among these interactions, we found salt bridges, hydrophobic interactions, and hydrogen bonds. Remarkably, salt bridges were the most relevant to prevent the elongation of the structure. In addition, the analysis of our results suggests which conformational movements are implicated in the activation/oligomerization of Bax. This atomistic description might have important implications for understanding the functionality and stability of Bax in vitro as well as within the cellular environment.
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Affiliation(s)
- Jorge Luis Rosas-Trigueros
- SEPI de la ESCOM del Instituto Politécnico Nacional, Juan de Dios Bátiz y Miguel Othón de Mendizábal s/n, México DF, México
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8
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García-Sáez AJ, Fuertes G, Suckale J, Salgado J. Permeabilization of the Outer Mitochondrial Membrane by Bcl-2 Proteins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 677:91-105. [DOI: 10.1007/978-1-4419-6327-7_8] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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9
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Yao Y, Bobkov AA, Plesniak LA, Marassi FM. Mapping the interaction of pro-apoptotic tBID with pro-survival BCL-XL. Biochemistry 2009; 48:8704-11. [PMID: 19670908 DOI: 10.1021/bi901171n] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The BH3-only BCL-2 family protein BID is activated by caspase-8 cleavage upon engagement of cell surface death receptors. The resulting 15 kDa C-terminal fragment, tBID, translocates to mitochondria, triggering the release of cytotoxic molecules and cell death. The pro-apoptotic activity of tBID is regulated by its interactions with pro-survival BCL-XL and pro-death BAX, both in the cytosol and at the mitochondrial membrane. In this study, we characterize the molecular interactions between full-length tBID and BCL-XL using NMR spectroscopy and isothermal titration calorimetry (ITC). In aqueous solution, tBID adopts an alpha-helical but dynamically disordered conformation; however, the three-dimensional conformation is stabilized when tBID engages its BH3 domain in the BH3-binding hydrophobic groove of BCL-XL to form a stable heterodimeric complex. Characterization of the binding thermodynamics by ITC reveals that the interaction between tBID and BCL-XL is driven by enthalpy but disfavored by the entropy associated with the conformational order induced in tBID upon binding BCL-XL.
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Affiliation(s)
- Yong Yao
- Burnham Institute for Medical Research, 10901 North Torrey Pines Road, La Jolla, California 92037, USA
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10
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Fanucchi S, Adamson RJ, Dirr HW. Formation of an Unfolding Intermediate State of Soluble Chloride Intracellular Channel Protein CLIC1 at Acidic pH. Biochemistry 2008; 47:11674-81. [DOI: 10.1021/bi801147r] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Sylvia Fanucchi
- Protein Structure-Function Research Unit, School of Molecular and Cell Biology, University of the Witwatersrand, Johannesburg 2050, South Africa
| | - Roslin J. Adamson
- Protein Structure-Function Research Unit, School of Molecular and Cell Biology, University of the Witwatersrand, Johannesburg 2050, South Africa
| | - Heini W. Dirr
- Protein Structure-Function Research Unit, School of Molecular and Cell Biology, University of the Witwatersrand, Johannesburg 2050, South Africa
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11
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Noble CG, Dong JM, Manser E, Song H. Bcl-xL and UVRAG cause a monomer-dimer switch in Beclin1. J Biol Chem 2008; 283:26274-82. [PMID: 18641390 DOI: 10.1074/jbc.m804723200] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Beclin1 has a key regulatory role in the initiation of autophagy and is a tumor suppressor. We have examined the interplay between viral or human Bcl-2-like proteins and UVRAG and their opposite effects on Beclin1. We show that Beclin1 forms a dimer in solution via its coiled-coil domain both in vivo and in vitro. Viral Bcl-2 binds independently to two sites on the Beclin1 dimer, one with high affinity and one with lower affinity, whereas human Bcl-x(L) binds both sites equally with relatively low affinity. UVRAG disrupts the Beclin1-dimer interface, forming a heterodimer with Beclin1, suggesting that this is how UVRAG causes its effects on Beclin1 to activate autophagy. Both Bcl-2-like proteins reduce the affinity of UVRAG for Beclin1 approximately 4-fold, suggesting that they stabilize the Beclin1 dimer. Moreover, coimmunoprecipitation assays show that UVRAG substantially reduces Beclin1 dimerization in vivo. These data explain the concentration-dependent interplay between Bcl-2, UVRAG, and Beclin1, as both tumor suppressors, UVRAG and Beclin1, have single-copy mutations in human cancers. Furthermore, our data suggest that an alternative strategy for developing anti-cancer compounds would be to disrupt the Beclin1-dimer interface.
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Affiliation(s)
- Christian G Noble
- Institute of Molecular and Cell Biology, 61 Biopolis Dr., Proteos, Singapore 138673
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12
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High-yield expression and purification of soluble forms of the anti-apoptotic Bcl-x(L) and Bcl-2 as TolAIII-fusion proteins. Protein Expr Purif 2008; 60:214-20. [PMID: 18522870 DOI: 10.1016/j.pep.2008.04.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2008] [Revised: 03/26/2008] [Accepted: 04/15/2008] [Indexed: 11/23/2022]
Abstract
A method is presented to produce large amounts of Bcl-2 and Bcl-x(L), two anti-apoptotic proteins of considerable biomedical interest. Expression constructs were prepared in which the Escherichia coli protein TolAIII, known to promote over expression of soluble product, was added to the N-terminus of Bcl-2 or Bcl-x(L) proteins, which had their C-terminal hydrophobic anchors deleted. Here the expression of these TolAIII-fusion constructs, followed by a two-step metal-affinity based purification protocol is described. The method delivers at least 20 and 10mg of more than 90% pure TolAIII-Bcl-x(L)DeltaC and TolAIII-Bcl-2(2)DeltaC proteins, respectively, per liter of E. coli cell culture. The proteins are released by proteolysis with thrombin providing > 12 mg of Bcl-x(L)DeltaC or > 6 mg of Bcl-2(2)DeltaC per liter of E. coli cell culture with a purity of more than 95%. Whereas Bcl-x(L)DeltaC is soluble both before and after TolAIII removal, Triton X-100 can significantly increase the extraction of TolAIII- Bcl-2(2)DeltaC from the bacterial cells and its subsequent solubility. Far-UV CD spectroscopy demonstrated that they both have an alpha-helical structure. Fluorescence spectroscopy was used to quantitatively analyze the binding of the respiratory inhibitor antimycin A to recombinant Bcl-2 and Bcl-x(L) proteins as well as the displacement of this ligand from the hydrophobic pocket with BH3 Bad-derived peptide. Purified Bcl-x(L)DeltaC and Bcl-2(2)DeltaC both protect isolated mitochondria from Bax-induced release of cytochrome c. The ensemble of data shows that the expressed proteins are correctly folded and functional. Therefore, the TolAIII-fusion system provides a convenient tool for functional characterization and structural studies of anti-apoptotic proteins.
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13
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Tang L, Hopper ED, Tong Y, Sadowsky JD, Peterson KJ, Gellman SH, Fitzgerald MC. H/D Exchange- and Mass Spectrometry-Based Strategy for the Thermodynamic Analysis of Protein−Ligand Binding. Anal Chem 2007; 79:5869-77. [PMID: 17580981 DOI: 10.1021/ac0700777] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The equilibrium unfolding properties of four model protein systems were characterized using SUPREX (stability of unpurified proteins from rates of H/D exchange). SUPREX is an H/D exchange- and mass spectrometry-based technique for measuring the free energy (DeltaGf) and m-value (deltaDeltaGf/delta[denaturant]) associated with the folding/unfolding reaction of a protein. The model proteins in this study (calmodulin, carbonic anhydrase II, RmlB, Bcl-xL) were chosen to test the applicability of SUPREX to the thermodynamic analysis of larger (> approximately 15 kDa) or multidomain proteins. In the absence of ligand, DeltaGf and m-values for these proteins could not be evaluated using the conventional data acquisition and analysis methods previously established for SUPREX. However, ligand-bound forms of the proteins were amenable to conventional SUPREX analyses, and it was possible to evaluate reasonably accurate and precise binding free energies of selected ligands. In some cases, protein-ligand dissociation constants (Kd values) could also be ascertained. The SUPREX-derived binding free energies and Kd values evaluated here were in good agreement with those reported on the same complexes using other techniques.
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Affiliation(s)
- Liangjie Tang
- Department of Chemistry, Duke University, Durham, North Carolina 27708, USA
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14
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Aisenbrey C, Sudheendra US, Ridley H, Bertani P, Marquette A, Nedelkina S, Lakey JH, Bechinger B. Helix orientations in membrane-associated Bcl-XL determined by 15N-solid-state NMR spectroscopy. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2007; 37:71-80. [PMID: 17492281 DOI: 10.1007/s00249-007-0165-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2007] [Revised: 03/22/2007] [Accepted: 03/31/2007] [Indexed: 11/24/2022]
Abstract
Controlled cell death is fundamental to tissue hemostasis and apoptosis malfunctions can lead to a wide range of diseases. Bcl-x(L) is an anti-apoptotic protein the function of which is linked to its reversible interaction with mitochondrial outer membranes. Its interfacial and intermittent bilayer association makes prediction of its bound structure difficult without using methods able to extract data from dynamic systems. Here we investigate Bcl-x(L) associated with oriented lipid bilayers at physiological pH using solid-state NMR spectroscopy. The data are consistent with a C-terminal transmembrane anchoring sequence and an average alignment of the remaining helices, i.e. including helices 5 and 6, approximately parallel to the membrane surface. Data from several biophysical approaches confirm that after removal of the C-terminus from Bcl-x(L) its membrane interactions are weak. In the presence of membranes Bcl-x(L) can still interact with a Bak BH3 domain peptide suggesting a model where the hydrophobic C-terminus of the protein unfolds and inserts into the membrane. During this conformational change the Bcl-x(L) hydrophobic binding pocket becomes accessible for protein-protein interactions whilst the structure of the N-terminal region remains intact.
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Affiliation(s)
- Christopher Aisenbrey
- Institut de Chimie de Strasbourg, Université Louis Pasteur/CNRS LC3-UMR 7177, 4 rue Blaise Pascal, 67070 Strasbourg, France
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15
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Oberstein A, Jeffrey PD, Shi Y. Crystal structure of the Bcl-XL-Beclin 1 peptide complex: Beclin 1 is a novel BH3-only protein. J Biol Chem 2007; 282:13123-32. [PMID: 17337444 DOI: 10.1074/jbc.m700492200] [Citation(s) in RCA: 459] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Bcl-2 family proteins are key regulators of apoptosis and have recently been shown to modulate autophagy. The tumor suppressor Beclin 1 has been proposed to coordinate both apoptosis and autophagy through direct interaction with anti-apoptotic family members Bcl-2 and/or Bcl-X(L). However, the molecular basis for this interaction remains enigmatic. Here we report that Beclin 1 contains a conserved BH3 domain, which is both necessary and sufficient for its interaction with Bcl-X(L). We also report the crystal structure of a Beclin BH3 peptide in complex with Bcl-X(L) at 2.5A resolution. Reminiscent of previously determined Bcl-X(L)-BH3 structures, the amphipathic BH3 helix of Beclin 1 bound to a conserved hydrophobic groove of Bcl-X(L). These results define Beclin 1 as a novel BH3-only protein, implying that Beclin 1 may have a direct role in initiating apoptotic signaling. We propose that this putative apoptotic function may be linked to the ability of Beclin 1 to suppress tumor formation in mammals.
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Affiliation(s)
- Adam Oberstein
- Lewis Thomas Laboratory, Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA
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16
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Thuduppathy GR, Terrones O, Craig JW, Basañez G, Hill RB. The N-terminal domain of Bcl-xL reversibly binds membranes in a pH-dependent manner. Biochemistry 2007; 45:14533-42. [PMID: 17128992 PMCID: PMC1764622 DOI: 10.1021/bi0616652] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Bcl-xL regulates apoptosis by maintaining the integrity of the mitochondrial outer membrane by adopting both soluble and membrane-associated forms. The membrane-associated conformation does not require a conserved, C-terminal transmembrane domain and appears to be inserted into the bilayer of synthetic membranes as assessed by membrane permeabilization and critical surface pressure measurements. Membrane association is reversible and is regulated by the cooperative binding of approximately two protons to the protein. Two acidic residues, Glu153 and Asp156, that lie in a conserved hairpin of Bcl-xLDeltaTM appear to be important in this process on the basis of a 16% increase in the level of membrane association of the double mutant E153Q/D156N. Contrary to that for the wild type, membrane permeabilization for the mutant is not correlated with membrane association. Monolayer surface pressure measurements suggest that this effect is primarily due to less membrane penetration. These results suggest that E153 and D156 are important for the Bcl-xLDeltaTM conformational change and that membrane binding can be distinct from membrane permeabilization. Taken together, these studies support a model in which Bcl-xL activity is controlled by reversible insertion of its N-terminal domain into the mitochondrial outer membrane. Future studies with Bcl-xL mutants such as E153Q/D156N should allow determination of the relative contributions of membrane binding, insertion, and permeabilization to the regulation of apoptosis.
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Affiliation(s)
| | | | | | | | - R. Blake Hill
- * To whom correspondence should be addressed: Department of Biology, Mudd Hall, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218. Phone: (410) 516-6783. Fax: (702) 441-2490. E-mail:
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Thuduppathy GR, Craig JW, Schon VKA, Hill RB. Evidence that membrane insertion of the cytosolic domain of Bcl-xL is governed by an electrostatic mechanism. J Mol Biol 2006; 359:1045-58. [PMID: 16650855 PMCID: PMC1785297 DOI: 10.1016/j.jmb.2006.03.052] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2005] [Revised: 03/16/2006] [Accepted: 03/21/2006] [Indexed: 11/30/2022]
Abstract
Signals from different cellular networks are integrated at the mitochondria in the regulation of apoptosis. This integration is controlled by the Bcl-2 proteins, many of which change localization from the cytosol to the mitochondrial outer membrane in this regulation. For Bcl-xL, this change in localization reflects the ability to undergo a conformational change from a solution to integral membrane conformation. To characterize this conformational change, structural and thermodynamic measurements were performed in the absence and presence of lipid vesicles with Bcl-xL. A pH-dependent model is proposed for the solution to membrane conformational change that consists of three stable conformations: a solution conformation, a conformation similar to the solution conformation but anchored to the membrane by its C-terminal transmembrane domain, and a membrane conformation that is fully associated with the membrane. This model predicts that the solution to membrane conformational change is independent of the C-terminal transmembrane domain, which is experimentally demonstrated. The conformational change is associated with changes in secondary and, especially, tertiary structure of the protein, as measured by far and near-UV circular dichroism spectroscopy, respectively. Membrane insertion was distinguished from peripheral association with the membrane by quenching of intrinsic tryptophan fluorescence by acrylamide and brominated lipids. For the cytosolic domain, the free energy of insertion (DeltaG degrees x) into lipid vesicles was determined to be -6.5 kcal mol(-1) at pH 4.9 by vesicle binding experiments. To test whether electrostatic interactions were significant to this process, the salt dependence of this conformational change was measured and analyzed in terms of Gouy-Chapman theory to estimate an electrostatic contribution of DeltaG degrees el approximately -2.5 kcal mol(-1) and a non-electrostatic contribution of DeltaG degrees nel approximately -4.0 kcal mol(-1) to the free energy of insertion, DeltaG degrees x. Calcium, which blocks ion channel activity of Bcl-xL, did not affect the solution to membrane conformational change more than predicted by these electrostatic considerations. The lipid cardiolipin, that is enriched at mitochondrial contact sites and reported to be important for the localization of Bcl-2 proteins, did not affect the solution to membrane conformational change of the cytosolic domain, suggesting that this lipid is not involved in the localization of Bcl-xL in vivo. Collectively, these data suggest the solution to membrane conformational change is controlled by an electrostatic mechanism. Given the distinct biological activities of these conformations, the possibility that this conformational change might be a regulatory checkpoint for apoptosis is discussed.
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Affiliation(s)
| | - Jeffrey W. Craig
- Department of Biology, Johns Hopkins University, 3400 N. Charles St,
Baltimore, MD 21218, USA
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