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Nomura K, Hayakawa K, Tatsumi H, Ono S. Actin-interacting Protein 1 Promotes Disassembly of Actin-depolymerizing Factor/Cofilin-bound Actin Filaments in a pH-dependent Manner. J Biol Chem 2016; 291:5146-56. [PMID: 26747606 DOI: 10.1074/jbc.m115.713495] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Indexed: 02/02/2023] Open
Abstract
Actin-interacting protein 1 (AIP1) is a conserved WD repeat protein that promotes disassembly of actin filaments when actin-depolymerizing factor (ADF)/cofilin is present. Although AIP1 is known to be essential for a number of cellular events involving dynamic rearrangement of the actin cytoskeleton, the regulatory mechanism of the function of AIP1 is unknown. In this study, we report that two AIP1 isoforms from the nematode Caenorhabditis elegans, known as UNC-78 and AIPL-1, are pH-sensitive in enhancement of actin filament disassembly. Both AIP1 isoforms only weakly enhance disassembly of ADF/cofilin-bound actin filaments at an acidic pH but show stronger disassembly activity at neutral and basic pH values. However, a severing-defective mutant of UNC-78 shows pH-insensitive binding to ADF/cofilin-decorated actin filaments, suggesting that the process of filament severing or disassembly, but not filament binding, is pH-dependent. His-60 of AIP1 is located near the predicted binding surface for the ADF/cofilin-actin complex, and an H60K mutation of AIP1 partially impairs its pH sensitivity, suggesting that His-60 is involved in the pH sensor for AIP1. These biochemical results suggest that pH-dependent changes in AIP1 activity might be a novel regulatory mechanism of actin filament dynamics.
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Affiliation(s)
- Kazumi Nomura
- From the Departments of Pathology and Cell Biology, Emory University, Atlanta, Georgia 30322
| | | | - Hitoshi Tatsumi
- Department of Physiology, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan, and the Department of Applied Biosciences, Kanazawa Institute of Technology, Kanazawa 924-0838, Japan
| | - Shoichiro Ono
- From the Departments of Pathology and Cell Biology, Emory University, Atlanta, Georgia 30322,
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Extracellular alkaline pH leads to increased metastatic potential of estrogen receptor silenced endocrine resistant breast cancer cells. PLoS One 2013; 8:e76327. [PMID: 24098477 PMCID: PMC3788134 DOI: 10.1371/journal.pone.0076327] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2013] [Accepted: 08/23/2013] [Indexed: 01/18/2023] Open
Abstract
Introduction Endocrine resistance in breast cancer is associated with enhanced metastatic potential and poor clinical outcome, presenting a significant therapeutic challenge. We have established several endocrine insensitive breast cancer lines by shRNA induced depletion of estrogen receptor (ER) by transfection of MCF-7 cells which all exhibit enhanced expression profile of mesenchymal markers with reduction of epithelial markers, indicating an epithelial to mesenchymal transition. In this study we describe their behaviour in response to change in extracellular pH, an important factor controlling cell motility and metastasis. Methods Morphological changes associated with cell exposure to extracellular alkaline pH were assessed by live cell microscopy and the effect of various ion pumps on this behavior was investigated by pretreatment with chemical inhibitors. The activity and expression profile of key signaling molecules was assessed by western blotting. Cell motility and invasion were examined by scratch and under-agarose assays respectively. Total matrix metalloproteinase (MMP) activity and specifically of MMP2/9 was assessed in conditioned medium in response to brief alkaline pH exposure. Results Exposure of ER –ve but not ER +ve breast cancer cells to extracellular alkaline pH resulted in cell shrinkage and spherical appearance (termed contractolation); this was reversed by returning the pH back to 7.4. Contractolation was blocked by targeting the Na+/K+ and Na+/H+ pumps with specific chemical inhibitors. The activity and expression profile of key signaling molecules critical for cell adhesion were modulated by the exposure to alkaline pH. Brief exposure to alkaline pH enhanced MMP2/9 activity and the invasive potential of ER –ve cells in response to serum components and epithelial growth factor stimulation without affecting unhindered motility. Conclusions Endocrine resistant breast cancer cells behave very differently to estrogen responsive cells in alkaline pH, with enhanced invasive potential; these studies emphasise the crucial influence of extracellular pH and caution against indiscriminate application of alkalinising drug therapy.
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Beaumont KG, Mrksich M. The mechanostability of isolated focal adhesions is strongly dependent on pH. CHEMISTRY & BIOLOGY 2012; 19:711-20. [PMID: 22726685 PMCID: PMC3476948 DOI: 10.1016/j.chembiol.2012.04.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2010] [Revised: 04/04/2012] [Accepted: 04/06/2012] [Indexed: 01/02/2023]
Abstract
This report demonstrates that the mechanical stability of focal adhesions exhibits a biphasic and sensitive pH dependence. These studies used isolated focal adhesions, which retain many of the properties of the intracellular structures, including protein composition and force-dependent reinforcement by cytosolic proteins. The focal adhesion structures are least stable to applied force at a pH of 6.4, and significantly more stable at slightly higher and lower pH values. This trend is consistent with previous work that characterized the pH dependence of cell migration and may therefore be relevant to controlling the invasiveness of metastatic cancer cells. This approach is significant because it allows biochemical studies of large protein complexes previously studied only in cell culture, and therefore offers new opportunities for performing mechanistic studies of a range of factors that contribute to focal adhesion stability.
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Affiliation(s)
- Kristin Grant Beaumont
- Departments of Biomedical Engineering, Chemistry, Cell & Molecular Biology and Howard Hughes Medical Institute; Northwestern University; Chicago, IL, 60611; USA
| | - Milan Mrksich
- Departments of Biomedical Engineering, Chemistry, Cell & Molecular Biology and Howard Hughes Medical Institute; Northwestern University; Chicago, IL, 60611; USA
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Abstract
Although cancer is a diverse set of diseases, cancer cells share a number of adaptive hallmarks. Dysregulated pH is emerging as a hallmark of cancer because cancers show a 'reversed' pH gradient with a constitutively increased intracellular pH that is higher than the extracellular pH. This gradient enables cancer progression by promoting proliferation, the evasion of apoptosis, metabolic adaptation, migration and invasion. Several new advances, including an increased understanding of pH sensors, have provided insight into the molecular basis for pH-dependent cell behaviours that are relevant to cancer cell biology. We highlight the central role of pH sensors in cancer cell adaptations and suggest how dysregulated pH could be exploited to develop cancer-specific therapeutics.
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Affiliation(s)
- Bradley A Webb
- Department of Cell and Tissue Biology, University of California, San Francisco, California 94143, USA
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Srivastava J, Barreiro G, Groscurth S, Gingras AR, Goult BT, Critchley DR, Kelly MJS, Jacobson MP, Barber DL. Structural model and functional significance of pH-dependent talin-actin binding for focal adhesion remodeling. Proc Natl Acad Sci U S A 2008; 105:14436-41. [PMID: 18780792 PMCID: PMC2532973 DOI: 10.1073/pnas.0805163105] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2008] [Indexed: 01/20/2023] Open
Abstract
Actin filament binding by the focal adhesion (FA)-associated protein talin stabilizes cell-substrate adhesions and is thought to be rate-limiting in cell migration. Although F-actin binding by talin is known to be pH-sensitive in vitro, with lower affinity at higher pH, the functional significance of this pH dependence is unknown. Because increased intracellular pH (pH(i)) promotes cell migration and is a hallmark of metastatic carcinomas, we asked whether it increases FA remodeling through lower-affinity talin-actin binding. Talin contains several actin binding sites, but we found that only the COOH-terminal USH-I/LWEQ module showed pH-dependent actin binding, with lower affinity and decreased maximal binding at higher pH. Molecular dynamics simulations and NMR of this module revealed a structural mechanism for pH-dependent actin binding. A cluster of titratable amino acids with upshifted pK(a) values, including His-2418, was identified at one end of the five-helix bundle distal from the actin binding site. Protonation of His-2418 induces changes in the conformation and dynamics of the remote actin binding site. Structural analyses of a mutant talin-H2418F at pH 6.0 and 8.0 suggested changes different from the WT protein, and we confirmed that actin binding by talin-H2418F was relatively pH-insensitive. In motile fibroblasts, increasing pH(i) decreased FA lifetime and increased the migratory rate. However, expression of talin-H2418F increased lifetime 2-fold and decreased the migratory rate. These data identify a molecular mechanism for pH-sensitive actin binding by talin and suggest that FA turnover is pH-dependent and in part mediated by pH-dependent affinity of talin for binding actin.
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Affiliation(s)
- J. Srivastava
- *Department of Cell and Tissue Biology, University of California, San Francisco, CA 94143
| | - G. Barreiro
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158-2517; and
| | - S. Groscurth
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158-2517; and
| | - A. R. Gingras
- Department of Biochemistry, University of Leicester, Lancaster Road, Leicester LE1 9HN, United Kingdom
| | - B. T. Goult
- Department of Biochemistry, University of Leicester, Lancaster Road, Leicester LE1 9HN, United Kingdom
| | - D. R. Critchley
- Department of Biochemistry, University of Leicester, Lancaster Road, Leicester LE1 9HN, United Kingdom
| | - M. J. S. Kelly
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158-2517; and
| | - M. P. Jacobson
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158-2517; and
| | - D. L. Barber
- *Department of Cell and Tissue Biology, University of California, San Francisco, CA 94143
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6
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Srivastava J, Barber D. Actin co-sedimentation assay; for the analysis of protein binding to F-actin. J Vis Exp 2008:690. [PMID: 19066573 DOI: 10.3791/690] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
The actin cytoskeleton within the cell is a network of actin filaments that allows the movement of cells and cellular processes, and that generates tension and helps maintains cellular shape. Although the actin cytoskeleton is a rigid structure, it is a dynamic structure that is constantly remodeling. A number of proteins can bind to the actin cytoskeleton. The binding of a particular protein to F-actin is often desired to support cell biological observations or to further understand dynamic processes due to remodeling of the actin cytoskeleton. The actin co-sedimentation assay is an in vitro assay routinely used to analyze the binding of specific proteins or protein domains with F-actin. The basic principles of the assay involve an incubation of the protein of interest (full length or domain of) with F-actin, ultracentrifugation step to pellet F-actin and analysis of the protein co-sedimenting with F-actin. Actin co-sedimentation assays can be designed accordingly to measure actin binding affinities and in competition assays.
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Affiliation(s)
- Jyoti Srivastava
- Department of Cell and Tissue Biology, University of California, San Francisco, USA
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Overlapping functions of the two talin homologues in Dictyostelium. EUKARYOTIC CELL 2008; 7:906-16. [PMID: 18375618 DOI: 10.1128/ec.00464-07] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Talin is a cytoskeletal protein involved in constructing and regulating focal adhesions in animal cells. The cellular slime mold Dictyostelium discoideum has two talin homologues, talA and talB, and earlier studies have characterized the single knockout mutants. talA(-) cells show reduced adhesion to the substrates and slightly impaired cytokinesis leading to a high proportion of multinucleated cells in the vegetative stage, while the development is normal. In contrast, talB(-) cells are characterized by reduced motility in the developmental stage, and they are arrested at the tight-mound stage. Here, we created and analyzed a double mutant with a disruption of both talA and talB. Defects in adhesion to the substrates, cytokinesis, and development were more severe in cells with a disruption of both talA and talB. The talA(-) talB(-) cells failed to attach to the substrates in the vegetative stage, exhibited a higher proportion of multinucleated cells than talA(-) cells, and showed more-reduced motility during the development and an earlier developmental arrest than talB(-) cells at the loose-mound stage. Moreover, overexpression of either talA or talB compensated for the loss of the other talin, respectively. The analysis of talA(-) talB(-) cells also revealed that talin was required for the formation of paxillin-rich adhesion sites and that there was another adhesion mechanism which is independent of talin in the developmental stage. This is the first study demonstrating overlapping functions of two talin homologues, and our data further indicate the importance of talin.
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Lim J, Wiedemann A, Tzircotis G, Monkley SJ, Critchley DR, Caron E. An essential role for talin during alpha(M)beta(2)-mediated phagocytosis. Mol Biol Cell 2007; 18:976-85. [PMID: 17202407 PMCID: PMC1805113 DOI: 10.1091/mbc.e06-09-0813] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The cytoskeletal, actin-binding protein talin has been previously implicated in phagocytosis in Dictyostelium discoideum and mammalian phagocytes. However, its mechanism of action during internalization is not understood. Our data confirm that endogenous talin can occasionally be found at phagosomes forming around IgG- and C3bi-opsonized red blood cells in macrophages. Remarkably, talin knockdown specifically abrogates uptake through complement receptor 3 (CR3, CD11b/CD18, alpha(M)beta(2) integrin) and not through the Fc gamma receptor. We show that talin physically interacts with CR3/alpha(M)beta(2) and that this interaction involves the talin head domain and residues W747 and F754 in the beta(2) integrin cytoplasmic domain. The CR3/alpha(M)beta(2)-talin head interaction controls not only talin recruitment to forming phagosomes but also CR3/alpha(M)beta(2) binding activity, both in macrophages and transfected fibroblasts. However, the talin head domain alone cannot support phagocytosis. Our results establish for the first time at least two distinct roles for talin during CR3/alpha(M)beta(2)-mediated phagocytosis, most noticeably activation of the CR3/alpha(M)beta(2) receptor and phagocytic uptake.
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Affiliation(s)
- Jenson Lim
- *Centre for Molecular Microbiology and Infection and Division of Cell and Molecular Biology, Imperial College London, London SW7 2AZ, United Kingdom; and
| | - Agnès Wiedemann
- *Centre for Molecular Microbiology and Infection and Division of Cell and Molecular Biology, Imperial College London, London SW7 2AZ, United Kingdom; and
| | - George Tzircotis
- *Centre for Molecular Microbiology and Infection and Division of Cell and Molecular Biology, Imperial College London, London SW7 2AZ, United Kingdom; and
| | - Susan J. Monkley
- Department of Biochemistry, University of Leicester, Leicester LE1 9HN, United Kingdom
| | - David R. Critchley
- Department of Biochemistry, University of Leicester, Leicester LE1 9HN, United Kingdom
| | - Emmanuelle Caron
- *Centre for Molecular Microbiology and Infection and Division of Cell and Molecular Biology, Imperial College London, London SW7 2AZ, United Kingdom; and
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Lee HS, Bellin RM, Walker DL, Patel B, Powers P, Liu H, Garcia-Alvarez B, de Pereda JM, Liddington RC, Volkmann N, Hanein D, Critchley DR, Robson RM. Characterization of an actin-binding site within the talin FERM domain. J Mol Biol 2004; 343:771-84. [PMID: 15465061 DOI: 10.1016/j.jmb.2004.08.069] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2004] [Revised: 08/10/2004] [Accepted: 08/16/2004] [Indexed: 11/24/2022]
Abstract
Talin is a large cytoskeletal protein that couples integrins to F-actin. Three actin-binding sites (ABS1-3) have been reported: one in the N-terminal head, and two in the C-terminal rod domain. Although the C-terminal ABS3 has been partially characterized, the presence and properties of ABS1 within the talin head are less well defined. We show here that the talin head binds F-actin in vitro and in vivo at a specific site within the actin filament. Thus, purified talin head liberated from gizzard talin by calpain cleavage cosediments with F-actin in a low salt buffer at pH 6.4 (conditions that are optimal for binding intact talin), and using recombinant polypeptides, we have mapped ABS1 to the FERM domain within the talin head. Both the F2 and F3 FERM subdomains contribute to binding, and EGFP-tagged FERM subdomains colocalize with actin stress fibers when expressed in COS cells. High-resolution electron microscopy of actin filaments decorated with F2F3 localizes binding to a site that is distinct from that recognized by members of the calponin-homology superfamily. Finally, we show that the FERM domain can couple F-actin to PIPkin, and by inference to integrins, since they bind to the same pocket in the F3 subdomain. This suggests that the talin FERM domain functions as a linker between PIPkin or integrins and F-actin at sites of cell-matrix adhesions.
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Affiliation(s)
- Ho-Sup Lee
- Muscle Biology Group, Departments of Biochemistry, Biophysics, and Molecular Biology and of Animal Science, Iowa State University, Ames, IA 50011-3260, USA
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Baumgartner M, Patel H, Barber DL. Na+/H+exchanger NHE1 as plasma membrane scaffold in the assembly of signaling complexes. Am J Physiol Cell Physiol 2004; 287:C844-50. [PMID: 15355855 DOI: 10.1152/ajpcell.00094.2004] [Citation(s) in RCA: 131] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The plasma membrane Na+/H+exchanger NHE1 has an established function in intracellular pH and cell volume homeostasis by catalyzing electroneutral influx of extracellular Na+and efflux of intracellular H+. A second function of NHE1 as a structural anchor for actin filaments through its direct binding of the ezrin, radixin, and moesin (ERM) family of actin-binding proteins was recently identified. ERM protein binding and actin anchoring by NHE1 are necessary to retain the localization of NHE1 in specialized plasma membrane domains and to promote cytoskeleton-dependent processes, including actin filament bundling and cell-substrate adhesions. This review explores a third function of NHE1, as a plasma membrane scaffold in the assembly of signaling complexes. Through its coordinate functions in H+efflux, actin anchoring, and scaffolding, we propose that NHE1 promotes protein interactions and activities, assembles signaling complexes in specialized plasma membrane domains, and coordinates divergent signaling pathways.
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Affiliation(s)
- Martin Baumgartner
- University of California, San Francisco, 513 Parnassus Ave., San Francisco, CA 94143, USA
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Brown NH, Gregory SL, Rickoll WL, Fessler LI, Prout M, White RAH, Fristrom JW. Talin is essential for integrin function in Drosophila. Dev Cell 2002; 3:569-79. [PMID: 12408808 DOI: 10.1016/s1534-5807(02)00290-3] [Citation(s) in RCA: 212] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
We show that the Drosophila gene rhea, isolated because its wing blister phenotype is typical of mutants affecting integrin function, encodes talin. Embryos deficient in talin have very similar phenotypes to integrin (betaPS) null embryos, including failure in germ band retraction and muscle detachment. We demonstrate that talin is not required for the presence of integrins on the cell surface or their localization at muscle termini. However, talin is required for formation of focal adhesion-like clusters of integrins on the basal surface of imaginal disc epithelia and junctional plaques between muscle and tendon cells. These results indicate that talin is essential for integrin function and acts by stably linking clusters of ECM-linked integrins to the cytoskeleton.
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Affiliation(s)
- Nicholas H Brown
- Wellcome Trust/Cancer Research UK Institute, University of Cambridge, United Kingdom.
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Isenberg G, Doerhoefer S, Hoekstra D, Goldmann WH. Membrane fusion induced by the major lipid-binding domain of the cytoskeletal protein talin. Biochem Biophys Res Commun 2002; 295:636-43. [PMID: 12099686 DOI: 10.1016/s0006-291x(02)00714-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Secondary structure predictions have led to the identification of a major membrane-anchoring domain of the cytoskeletal protein talin spanning from amino acid 385 to 406. Using a synthetically derived peptide of this region, researchers have shown that it inserts into POPC/POPG phospholipid membranes with a partition coefficient of K(app)=1.1+/-0.2 x 10(5) M(-1) and has an average molar reaction enthalpy of DeltaH=-2.5 kcal/mol, as determined by monolayer expansion technique and isothermic titration calorimetry [J. Biol. Chem. 275, 17954]. We applied resonance energy transfer (RET) assays to analyze the fusogenic properties of this peptide by lipid mixing and used liposomes containing carboxyfluorescein to measure the contents leakage. We directly visualized talin peptide-induced vesicle membrane fusion using cryo-electron microscopy. This is the first example of a cytoskeletal protein domain that can trigger membrane fusion that might be of importance for understanding membrane targeting and motile events at the leading edge of the cell.
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Affiliation(s)
- Gerhard Isenberg
- Department of Biophysics E22, Technical University Munich, James-Franck-Str., D-85748 Garching, Germany
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Goldmann WH. Binding of tropomyosin-troponin to actin increases filament bending stiffness. Biochem Biophys Res Commun 2000; 276:1225-8. [PMID: 11027614 DOI: 10.1006/bbrc.2000.3608] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Rheologic measurements show that the association of tropomyosin-troponin with actin filaments is responsible for the reduction of the internal chain dynamic and increase in the mechanical rigidity of actin filaments. Basing calculations on the linear relation between the plateau modulus, G(N)('), and bending modulus, kappa, I find that tropomyosin-troponin at r(AT) = 7 increases actin filament stiffness by approximately 50%. This is confirmed by dynamic light scattering. Further increases are observed at rising F-actin and constant tropomyosin-troponin concentrations. Tropomyosin-troponin also delays actin assembly and subsequent network formation and increases filament stiffness over time.
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Affiliation(s)
- W H Goldmann
- Departments of Pathology and Surgery, Children's Hospital, Boston, Massachusetts, 02115, USA
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Seelig A, Blatter XL, Frentzel A, Isenberg G. Phospholipid binding of synthetic talin peptides provides evidence for an intrinsic membrane anchor of talin. J Biol Chem 2000; 275:17954-61. [PMID: 10748069 DOI: 10.1074/jbc.m002264200] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Talin, an actin-binding protein, is assumed to anchor at the membrane via an intrinsic amino acid sequence. Three N-terminal talin fragments, 21-39 (S19), 287-304 (H18), and 385-406 (H17) have been proposed as potential membrane anchors. The interaction of the corresponding synthetic peptides with lipid model systems was investigated with CD spectroscopy, isothermal titration calorimetry, and monolayer expansion measurements. The membrane model systems were neutral or negatively charged small unilamellar vesicles or monolayers with a lateral packing density of bilayers (32 mN/m). S19 partitions into charged monolayers/bilayers with a penetration area A(p) = 140 +/- 30 A(2) and a free energy of binding of DeltaG(0) = -5.7 kcal/mol, thereby forming a partially alpha-helical structure. H18 does not interact with lipid monolayers or bilayers. H17 penetrates into neutral and charged monolayers/bilayers with A(p) = 148 +/- 23 A(2) and A(p) = 160 +/- 15 A(2), respectively, forming an alpha-helix in the membrane-bound state. Membrane partitioning is mainly entropy-driven. Under physiological conditions the free energy of binding to negatively charged membranes is DeltaG(0) = -9. 4 kcal/mol with a hydrophobic contribution of DeltaG(h) = -7.8 kcal/mol, comparable to that of post-translationally attached membrane anchors, and an electrostatic contribution of DeltaG(h) = -1.6 kcal/mol. The latter becomes more negative with decreasing pH. We show that H17 provides the binding energy required for a membrane anchor.
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Affiliation(s)
- A Seelig
- Department of Biophysical Chemistry, Biocenter, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.
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