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Morimoto YV. Ion Signaling in Cell Motility and Development in Dictyostelium discoideum. Biomolecules 2024; 14:830. [PMID: 39062545 PMCID: PMC11274586 DOI: 10.3390/biom14070830] [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: 06/12/2024] [Revised: 07/08/2024] [Accepted: 07/09/2024] [Indexed: 07/28/2024] Open
Abstract
Cell-to-cell communication is fundamental to the organization and functionality of multicellular organisms. Intercellular signals orchestrate a variety of cellular responses, including gene expression and protein function changes, and contribute to the integrated functions of individual tissues. Dictyostelium discoideum is a model organism for cell-to-cell interactions mediated by chemical signals and multicellular formation mechanisms. Upon starvation, D. discoideum cells exhibit coordinated cell aggregation via cyclic adenosine 3',5'-monophosphate (cAMP) gradients and chemotaxis, which facilitates the unicellular-to-multicellular transition. During this process, the calcium signaling synchronizes with the cAMP signaling. The resulting multicellular body exhibits organized collective migration and ultimately forms a fruiting body. Various signaling molecules, such as ion signals, regulate the spatiotemporal differentiation patterns within multicellular bodies. Understanding cell-to-cell and ion signaling in Dictyostelium provides insight into general multicellular formation and differentiation processes. Exploring cell-to-cell and ion signaling enhances our understanding of the fundamental biological processes related to cell communication, coordination, and differentiation, with wide-ranging implications for developmental biology, evolutionary biology, biomedical research, and synthetic biology. In this review, I discuss the role of ion signaling in cell motility and development in D. discoideum.
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Affiliation(s)
- Yusuke V. Morimoto
- Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, 680-4 Kawazu, Iizuka 820-8502, Fukuoka, Japan;
- Japan Science and Technology Agency, PRESTO, 4-1-8 Honcho, Kawaguchi 332-0012, Saitama, Japan
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2
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Singh JKD, Darley E, Ridone P, Gaston JP, Abbas A, Wickham SFJ, Baker MAB. Binding of DNA origami to lipids: maximizing yield and switching via strand displacement. Nucleic Acids Res 2021; 49:10835-10850. [PMID: 34614184 PMCID: PMC8565350 DOI: 10.1093/nar/gkab888] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2021] [Revised: 09/01/2021] [Accepted: 09/20/2021] [Indexed: 01/02/2023] Open
Abstract
Liposomes are widely used as synthetic analogues of cell membranes and for drug delivery. Lipid-binding DNA nanostructures can modify the shape, porosity and reactivity of liposomes, mediated by cholesterol modifications. DNA nanostructures can also be designed to switch conformations by DNA strand displacement. However, the optimal conditions to facilitate stable, high-yield DNA–lipid binding while allowing controlled switching by strand displacement are not known. Here, we characterized the effect of cholesterol arrangement, DNA structure, buffer and lipid composition on DNA–lipid binding and strand displacement. We observed that binding was inhibited below pH 4, and above 200 mM NaCl or 40 mM MgCl2, was independent of lipid type, and increased with membrane cholesterol content. For simple motifs, binding yield was slightly higher for double-stranded DNA than single-stranded DNA. For larger DNA origami tiles, four to eight cholesterol modifications were optimal, while edge positions and longer spacers increased yield of lipid binding. Strand displacement achieved controlled removal of DNA tiles from membranes, but was inhibited by overhang domains, which are used to prevent cholesterol aggregation. These findings provide design guidelines for integrating strand displacement switching with lipid-binding DNA nanostructures. This paves the way for achieving dynamic control of membrane morphology, enabling broader applications in nanomedicine and biophysics.
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Affiliation(s)
- Jasleen Kaur Daljit Singh
- School of Chemistry, The University of Sydney, Sydney, New South Wales, Australia.,School of Chemical and Biomolecular Engineering, The University of Sydney, Sydney, New South Wales, Australia.,The University of Sydney Nano Institute, The University of Sydney, Sydney, New South Wales, Australia
| | - Esther Darley
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, Australia
| | - Pietro Ridone
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, Australia
| | - James P Gaston
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, Australia
| | - Ali Abbas
- School of Chemical and Biomolecular Engineering, The University of Sydney, Sydney, New South Wales, Australia.,The University of Sydney Nano Institute, The University of Sydney, Sydney, New South Wales, Australia
| | - Shelley F J Wickham
- School of Chemistry, The University of Sydney, Sydney, New South Wales, Australia.,The University of Sydney Nano Institute, The University of Sydney, Sydney, New South Wales, Australia.,School of Physics, The University of Sydney, Sydney, New South Wales, Australia
| | - Matthew A B Baker
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, Australia.,CSIRO Synthetic Biology Future Science Platform, Brisbane, Australia
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Bhattacharjee N, Rani P, Biswas P. Capturing molten globule state of α-lactalbumin through constant pH molecular dynamics simulations. J Chem Phys 2013; 138:095101. [PMID: 23485328 DOI: 10.1063/1.4793470] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The recently developed methods of constant pH molecular dynamics directly captures the correlation between protonation and conformation to probe protein structure, function, and dynamics. In this work, we investigate the effect of pH on the conformational properties of the protein human α-lactalbumin. Constant pH simulations at both acidic and alkaline medium indicate the formation of the molten globule state, which is in accordance with the previous experimental observations (especially, in acidic medium). The size of the protein measured by its radius of gyration (RG) exhibits a marked increase in both acidic and alkaline medium, which matches with the corresponding experimentally observed value of RG found in the molten globule. The probability of native contacts is also considerably reduced at acidic and basic pH as compared to that of native structure crystallized at neutral pH. The mean fractal dimension D2 of the protein records a sharp increase in basic medium as compared to those in neutral and acidic solutions implying a significant pH induced conformational change. The mean square fluctuations of all residues of the entire protein are found to increase by several folds in both acidic and basic medium, which may be correlated with the normalized solvent accessibility of the residues indicating role of solvent accessible surface area on protein internal dynamics. The helices comprising the α-domain of the protein are moderately preserved in the acidic and alkaline pH. However, the β-sheet structures present in the β-domain are completely disrupted in both acidic as well as basic pH.
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Cytoskeletal interactions at the nuclear envelope mediated by nesprins. Int J Cell Biol 2012; 2012:736524. [PMID: 22518138 PMCID: PMC3296292 DOI: 10.1155/2012/736524] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2011] [Revised: 10/13/2011] [Accepted: 10/18/2011] [Indexed: 11/29/2022] Open
Abstract
Nesprin-1 is a giant tail-anchored nuclear envelope protein composed of an N-terminal F-actin binding domain, a long linker region formed by multiple spectrin repeats and a C-terminal transmembrane domain. Based on this structure, it connects the nucleus to the actin cytoskeleton. Earlier reports had shown that Nesprin-1 binds to nuclear envelope proteins emerin and lamin through C-terminal spectrin repeats. These repeats can also self-associate. We focus on the N-terminal Nesprin-1 sequences and show that they interact with Nesprin-3, a further member of the Nesprin family, which connects the nucleus to the intermediate filament network. We show that upon ectopic expression of Nesprin-3 in COS7 cells, which are nearly devoid of Nesprin-3 in vitro, vimentin filaments are recruited to the nucleus and provide evidence for an F-actin interaction of Nesprin-3 in vitro. We propose that Nesprins through interactions amongst themselves and amongst the various Nesprins form a network around the nucleus and connect the nucleus to several cytoskeletal networks of the cell.
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5
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Abstract
V-ATPase (vesicular H(+)-ATPase)-driven intravesicular acidification is crucial for vesicular trafficking. Defects in vesicular acidification and trafficking have recently been recognized as essential determinants of various human diseases. An important role of endosomal acidification in receptor-ligand dissociation and in activation of lysosomal hydrolytic enzymes is well established. However, the molecular mechanisms by which luminal pH information is transmitted to the cytosolic small GTPases that control trafficking events such as budding, coat formation and fusion are unknown. Here, we discuss our recent discovery that endosomal V-ATPase is a pH-sensor regulating the degradative pathway. According to our model, V-ATPase is responsible for: (i) the generation of a pH gradient between vesicular membranes; (ii) sensing of intravesicular pH; and (iii) transmitting this information to the cytosolic side of the membrane. We also propose the hypothetical molecular mechanism involved in function of the V-ATPase a2-subunit as a putative pH-sensor. Based on extensive experimental evidence on the crucial role of histidine residues in the function of PSPs (pH-sensing proteins) in eukaryotic cells, we hypothesize that pH-sensitive histidine residues within the intra-endosomal loops and/or C-terminal luminal tail of the a2-subunit could also be involved in the pH-sensing function of V-ATPase. However, in order to identify putative pH-sensitive histidine residues and to test this hypothesis, it is absolutely essential that we increase our understanding of the folding and transmembrane topology of the a-subunit isoforms of V-ATPase. Thus the crucial role of intra-endosomal histidine residues in pH-dependent conformational changes of the V-ATPase a2-isoform, its interaction with cytosolic small GTPases and ultimately in its acidification-dependent regulation of the endosomal/lysosomal protein degradative pathway remain to be determined.
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Endocytosis and the Actin Cytoskeleton in Dictyostelium discoideum. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2008; 267:343-97. [DOI: 10.1016/s1937-6448(08)00633-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Hinas A, Reimegård J, Wagner EGH, Nellen W, Ambros VR, Söderbom F. The small RNA repertoire of Dictyostelium discoideum and its regulation by components of the RNAi pathway. Nucleic Acids Res 2007; 35:6714-26. [PMID: 17916577 PMCID: PMC2175303 DOI: 10.1093/nar/gkm707] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Small RNAs play crucial roles in regulation of gene expression in many eukaryotes. Here, we report the cloning and characterization of 18–26 nt RNAs in the social amoeba Dictyostelium discoideum. This survey uncovered developmentally regulated microRNA candidates whose biogenesis, at least in one case, is dependent on a Dicer homolog, DrnB. Furthermore, we identified a large number of 21 nt RNAs originating from the DIRS-1 retrotransposon, clusters of which have been suggested to constitute centromeres. Small RNAs from another retrotransposon, Skipper, were significantly up-regulated in strains depleted of the second Dicer-like protein, DrnA, and a putative RNA-dependent RNA polymerase, RrpC. In contrast, the expression of DIRS-1 small RNAs was not altered in any of the analyzed strains. This suggests the presence of multiple RNAi pathways in D. discoideum. In addition, we isolated several small RNAs with antisense complementarity to mRNAs. Three of these mRNAs are developmentally regulated. Interestingly, all three corresponding genes express longer antisense RNAs from which the small RNAs may originate. In at least one case, the longer antisense RNA is complementary to the spliced but not the unspliced pre-mRNA, indicating synthesis by an RNA-dependent RNA polymerase.
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Affiliation(s)
- Andrea Hinas
- Department of Molecular Biology, Biomedical Center, Swedish University of Agricultural Sciences, Box 590, SE-75124 Uppsala, Sweden
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8
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Stern HA. Molecular simulation with variable protonation states at constant pH. J Chem Phys 2007; 126:164112. [PMID: 17477594 DOI: 10.1063/1.2731781] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
A new method is presented for performing molecular simulations at constant pH. The method is a Monte Carlo procedure where trial moves consist of relatively short molecular dynamics trajectories, using a time-dependent potential energy that interpolates between the old and new protonation states. Conformations and protonation states are sampled from the correct statistical ensemble independent of the trial-move trajectory length, which may be adjusted to optimize efficiency. Because moves are not instantaneous, the method does not require the use of a continuum solvation model. It should also be useful in describing buried titratable groups that are not directly exposed to solvent, but have strong interactions with neighboring hydrogen bond partners. The feasibility of the method is demonstrated for a simple test case: constant-pH simulations of acetic acid in aqueous solution with an explicit representation of water molecules.
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Affiliation(s)
- Harry A Stern
- Department of Chemistry, University of Rochester, Rochester, New York 14627, USA
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9
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Patel H, Barber DL. A developmentally regulated Na-H exchanger in Dictyostelium discoideum is necessary for cell polarity during chemotaxis. ACTA ACUST UNITED AC 2005; 169:321-9. [PMID: 15851518 PMCID: PMC2171856 DOI: 10.1083/jcb.200412145] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Increased intracellular H+ efflux is speculated to be an evolutionarily conserved mechanism necessary for rapid assembly of cytoskeletal filaments and for morphological polarity during cell motility. In Dictyostelium discoideum, increased intracellular pH through undefined transport mechanisms plays a key role in directed cell movement. We report that a developmentally regulated Na-H exchanger in Dictyostelium discoideum (DdNHE1) localizes to the leading edge of polarized cells and is necessary for intracellular pH homeostasis and for efficient chemotaxis. Starved DdNHE1-null cells (Ddnhe1−) differentiate, and in response to the chemoattractant cAMP they retain directional sensing; however, they cannot attain a polarized morphology, but instead extend mislocalized pseudopodia around the cell and exhibit decreased velocity. Consistent with impaired polarity, in response to chemoattractant, Ddnhe1− cells lack a leading edge localization of F-actin and have significantly attenuated de novo F-actin polymerization but increased abundance of membrane-associated phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3). These findings indicate that during chemotaxis DdNHE1 is necessary for establishing the kinetics of actin polymerization and PI(3,4,5)P3 production and for attaining a polarized phenotype.
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Affiliation(s)
- Hitesh Patel
- Department of Cell and Tissue Biology, University of California, San Francisco, 4143, USA
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10
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Abstract
Cell protrusions are outward extensions of the plasma membrane of individual cells that function in sensing the cell environment and in making initial, dynamic adhesions to extracellular matrix and other cells. Cell protrusions can be grouped into two major categories on the basis of morphology: localized, finger-like structures of highly defined shape and various lengths; or broad, irregular extensions of the plasma membrane. A key requirement of all cell protrusions is the need for a rigid cytoskeleton to support the localized extension of the plasma membrane. This is achieved either by a core unipolar bundle of actin microfilaments in finger-like protrusions, or by a combination of radial, rib-like, actin bundles integrated with a dendritic meshwork of microfilaments in the broad, lamellipodial protrusions. From studies of multiple cell types in vertebrates and invertebrates, fascin-1 has emerged as an actin-bundling protein of general importance for a diverse set of cell protrusions with functions in cell adhesion, cell interactions, and cell migration. This review discusses current knowledge of the molecular and cellular properties and functions of fascin, the roles of fascin-based protrusions in the cardiovascular system in health and disease, and areas of future interest.
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Affiliation(s)
- Josephine C Adams
- Department of Cell Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
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11
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Hanakam F, Gerisch G. Monitoring intracellular shutting of histidine-rich pH sensor proteins tagged with green fluorescent protein. Methods Enzymol 2003; 302:51-8. [PMID: 12876762 DOI: 10.1016/s0076-6879(99)02009-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/03/2023]
Affiliation(s)
- F Hanakam
- Micromet GmbH, D-82152 Martinsried, Germany
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12
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Benedetti CE, Kobarg J, Pertinhez TA, Gatti RM, de Souza ON, Spisni A, Meneghini R. Plasmodium falciparum histidine-rich protein II binds to actin, phosphatidylinositol 4,5-bisphosphate and erythrocyte ghosts in a pH-dependent manner and undergoes coil-to-helix transitions in anionic micelles. Mol Biochem Parasitol 2003; 128:157-66. [PMID: 12742582 DOI: 10.1016/s0166-6851(03)00057-4] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The recombinant histidine-rich protein II (HRPII) from Plasmodium falciparum was shown to bind actin and phosphatidylinositol 4,5-bisphosphate (PIP(2)) in vitro in a pH-dependent manner, very similar to hisactophilin, an actin-binding protein from ameba. Binding of HRPII to actin and PIP(2) occurred at pH 6.0 and 6.5, but not above pH 7.0. Circular dichroism (CD) spectroscopy confirmed that HRPII interacts with actin at pH below 7.0, as judged by the changes induced in the secondary structure of the HRPII/actin mixture. Further CD analysis demonstrated that HRPII adopts a predominantly alpha-helical conformation with anionic micelles of PIP(2) and SDS, but not with neutral micelles of phosphatidylcholine (PC), a feature that is common to many actin-binding proteins involved in cytoskeleton remodeling. Similarly to hisactophilin, a GFP-HRPII fusion protein shuttled from the cytoplasm to the nucleus of HeLa cells as the cellular pH was lowered from 8.0 to 6.0. HeLa cells transfected with the HRPII gene showed increased levels of histidine-rich proteins (HRPs) in the soluble cell fraction at pH 8.0. At pH 6.0, however, HRPs were detected mainly in the insoluble cell fraction. Interestingly, we found that HRPII binds to human erythrocyte membranes at pH 6.0 and 6.5 but not at pH above 7.0. Our results point to remarkable similarities between HRPII, hisactophilin, and actin-binding proteins. Possible roles of the HRPII during Plasmodium infection are discussed in the light of these findings.
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Affiliation(s)
- Celso Eduardo Benedetti
- Centro de Biologia Molecular Estrutural (CEBIME), Laboratório Nacional de Luz Sincrotron (LNLS), CP6192, Campinas, SP CEP 13084-971, Brazil.
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13
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Kay CWM, Schleicher E, Kuppig A, Hofner H, Rüdiger W, Schleicher M, Fischer M, Bacher A, Weber S, Richter G. Blue light perception in plants. Detection and characterization of a light-induced neutral flavin radical in a C450A mutant of phototropin. J Biol Chem 2003; 278:10973-82. [PMID: 12525505 DOI: 10.1074/jbc.m205509200] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The LOV2 domain of Avena sativa phototropin and its C450A mutant were expressed as recombinant fusion proteins and were examined by optical spectroscopy, electron paramagnetic resonance, and electron-nuclear double resonance. Upon irradiation (420-480 nm), the LOV2 C450A mutant protein gave an optical absorption spectrum characteristic of a flavin radical even in the absence of exogenous electron donors, thus demonstrating that the flavin mononucleotide (FMN) cofactor in its photogenerated triplet state is a potent oxidant for redox-active amino acid residues within the LOV2 domain. The FMN radical in the LOV2 C450A mutant is N(5)-protonated, suggesting that the local pH close to the FMN is acidic enough so that the cysteine residue in the wild-type protein is likely to be also protonated. An electron paramagnetic resonance analysis of the photogenerated FMN radical gave information on the geometrical and electronic structure and the environment of the FMN cofactor. The experimentally determined hyperfine couplings of the FMN radical point to a highly restricted delocalization of the unpaired electron spin in the isoalloxazine moiety. In the light of these results a possible radical-pair mechanism for the formation of the FMN-C(4a)-cysteinyl adduct in LOV domains is discussed.
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Affiliation(s)
- Christopher W M Kay
- Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
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Sawai S, Hirano T, Maeda Y, Sawada Y. Rapid patterning and zonal differentiation in a two-dimensionalDictyosteliumcell mass: the role of pH and ammonia. J Exp Biol 2002; 205:2583-90. [PMID: 12151364 DOI: 10.1242/jeb.205.17.2583] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYRecently it was demonstrated that a rapidly forming, self-organizing pattern that emerges within two-dimensional Dictyostelium discoideumcell cultures could later give rise to stripes of distinct zones, each comprising different cell types. Here we report physiological aspects of the initial rapid patterning and its relationship to cell differentiation. We found that as the temperature is lowered the characteristic length of the pattern increases. From this we estimated the activation energy of the patterning kinetics. Fluorescence of fluorescein-conjugated dextran revealed that the cytosolic pH of cells in the inside zone becomes lower than that in the outer zone facing the air. The patterning could be inhibited by addition of the plasma-membrane proton pump inhibitors diethystilbestrol (DES) or miconazole. Preincubation of cells with weak acid delayed the timing of the patterning, whereas weak base hastened it. A pH-indicating dye revealed localized accumulation of ammonia in the extracellular space. These results suggest that gradients of secreted metabolites may be directly responsible for the rapid patterning and its consequence on cell differentiation in a confined geometrical situation. Possible diffusible candidate molecules and a reaction scheme coupled to the imposed oxygen gradient are discussed.
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Affiliation(s)
- Satoshi Sawai
- Graduate School of Information Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
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15
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Bürgi R, Kollman PA, Van Gunsteren WF. Simulating proteins at constant pH: An approach combining molecular dynamics and Monte Carlo simulation. Proteins 2002; 47:469-80. [PMID: 12001225 DOI: 10.1002/prot.10046] [Citation(s) in RCA: 142] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
For the structure and function of proteins, the pH of the solution is one of the determining parameters. Current molecular dynamics (MD) simulations account for the solution pH only in a limited way by keeping each titratable site in a chosen protonation state. We present an algorithm that generates trajectories at a Boltzmann distributed ensemble of protonation states by a combination of MD and Monte Carlo (MC) simulation. The algorithm is useful for pH-dependent structural studies and to investigate in detail the titration behavior of proteins. The method is tested on the acidic residues of the protein hen egg white lysozyme. It is shown that small structural changes may have a big effect on the pK(A) values of titratable residues.
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Affiliation(s)
- Roland Bürgi
- Laboratory of Physical Chemistry, Swiss Federal Institute of Technology Zürich, Zürich, Switzerland
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16
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Friedl P, Borgmann S, Bröcker E. Amoeboid leukocyte crawling through extracellular matrix: lessons from the
Dictyostelium
paradigm of cell movement. J Leukoc Biol 2001. [DOI: 10.1189/jlb.70.4.491] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Affiliation(s)
- Peter Friedl
- Cell Migration Laboratory, Department of Dermatology, University of Würzburg, Würzburg, Germany
| | - Stefan Borgmann
- Cell Migration Laboratory, Department of Dermatology, University of Würzburg, Würzburg, Germany
| | - Eva‐B. Bröcker
- Cell Migration Laboratory, Department of Dermatology, University of Würzburg, Würzburg, Germany
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17
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Bell-Parikh LC, Eipper BA, Mains RE. Response of an integral granule membrane protein to changes in pH. J Biol Chem 2001; 276:29854-63. [PMID: 11395514 DOI: 10.1074/jbc.m103936200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A key feature of the regulated secretory pathway in neuroendocrine cells is lumenal pH, which decreases between trans-Golgi network and mature secretory granules. Because peptidylglycine alpha-amidating monooxygenase (PAM) is one of the few membrane-spanning proteins concentrated in secretory granules and is a known effector of regulated secretion, we examined its sensitivity to pH. Based on antibody binding experiments, the noncatalytic linker regions between the two enzymatic domains of PAM show pH-dependent conformational changes; these changes occur in the presence or absence of a transmembrane domain. Integral membrane PAM-1 solubilized from rat anterior pituitary or from transfected AtT-20 cells aggregates reversibly at pH 5.5 while retaining enzyme activity. Over 35% of the PAM-1 in anterior pituitary extracts aggregates at pH 5.5, whereas only about 5% aggregates at pH 7.5. PAM-1 recovered from secretory granules and endosomes is highly responsive to low pH-induced aggregation, whereas PAM-1 recovered from a light, intracellular recycling compartment is not. Mutagenesis studies indicate that a transmembrane domain is necessary but not sufficient for low pH-induced aggregation and reveal a short lumenal, juxtamembrane segment that also contributes to pH-dependent aggregation. Taken together, these results demonstrate that several properties of membrane PAM serve as indicators of granule pH in neuroendocrine cells.
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Affiliation(s)
- L C Bell-Parikh
- Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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18
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Maranda B, Brown D, Bourgoin S, Casanova JE, Vinay P, Ausiello DA, Marshansky V. Intra-endosomal pH-sensitive recruitment of the Arf-nucleotide exchange factor ARNO and Arf6 from cytoplasm to proximal tubule endosomes. J Biol Chem 2001; 276:18540-50. [PMID: 11278939 DOI: 10.1074/jbc.m011577200] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Kidney proximal tubule epithelial cells have an extensive apical endocytotic apparatus that is critical for the reabsorption and degradation of proteins that traverse the glomerular filtration barrier and that is also involved in the extensive recycling of functionally important apical plasma membrane transporters. We show here that an Arf-nucleotide exchange factor, ARNO (ADP-ribosylation factor nucleotide site opener) as well as Arf6 and Arf1 small GTPases are located in the kidney proximal tubule receptor-mediated endocytosis pathway, and that ARNO and Arf6 recruitment from cytosol to endosomes is pH-dependent. In proximal tubules in situ, ARNO and Arf6 partially co-localized with the V-ATPase in apical endosomes in proximal tubules. Arf1 was localized both at the apical pole of proximal tubule epithelial cells, but also in the Golgi. By Western blot analysis ARNO, Arf6, and Arf1 were detected both in purified endosomes and in proximal tubule cytosol. A translocation assay showed that ATP-driven endosomal acidification triggered the recruitment of ARNO and Arf6 from proximal tubule cytosol to endosomal membranes. The translocation of both ARNO and Arf6 was reversed by V-type ATPase inhibitors and by uncouplers of endosomal intralumenal pH, and was correlated with the magnitude of intra-endosomal acidification. Our data suggest that V-type ATPase-dependent acidification stimulates the selective recruitment of ARNO and Arf6 to proximal tubule early endosomes. This mechanism may play an important role in the pH-dependent regulation of receptor-mediated endocytosis in proximal tubules in situ.
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Affiliation(s)
- B Maranda
- Program in Membrane Biology & Renal Unit, Massachusetts General Hospital, and Department of Medicine, Harvard Medical School, Boston, Massachusetts, 02129-2020, USA
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19
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Liu C, Chu D, Wideman RD, Houliston RS, Wong HJ, Meiering EM. Thermodynamics of denaturation of hisactophilin, a beta-trefoil protein. Biochemistry 2001; 40:3817-27. [PMID: 11300762 DOI: 10.1021/bi002609i] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Hisactophilin is a histidine-rich pH-dependent actin-binding protein from Dictyostelium discoideum. The structure of hisactophilin is typical of the beta-trefoil fold, a common structure adopted by diverse proteins with unrelated primary sequences and functions. The thermodynamics of denaturation of hisactophilin have been measured using fluorescence- and CD-monitored equilibrium urea denaturation curves, pH-denaturation, and thermal denaturation curves, as well as differential scanning calorimetry. Urea denaturation is reversible from pH 5.7 to pH 9.7; however, thermal denaturation is highly reversible only below pH approximately 6.2. Reversible denaturation by urea and heat is well fit using a two-state transition between the native and the denatured states. Urea denaturation curves are best fit using a quadratic dependence of the Gibbs free energy of unfolding upon urea concentration. Hisactophilin has moderate, roughly constant stability from pH 7.7 to pH 9.7; however, below pH 7.7, stability decreases markedly, most likely due to protonation of histidine residues. Enthalpic effects of histidine ionization upon unfolding also appear to be involved in the occurrence of cold unfolding of hisactophilin under relatively mild solution conditions. The stability data for hisactophilin are compared with data on hisactophilin function, and with data for two other beta-trefoil proteins, human interleukin-1beta, and basic fibroblast growth factor.
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Affiliation(s)
- C Liu
- Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
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20
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Maniak M. Fluid-phase uptake and transit in axenic Dictyostelium cells. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1525:197-204. [PMID: 11257433 DOI: 10.1016/s0304-4165(01)00105-2] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The main route for fluid-phase uptake in Dictyostelium is macropinocytosis, a process powered by the actin cytoskeleton. Nutrients within the endocytosed fluid are digested and resorbed, disposal of remnants follows by exocytosis. Along the endocytic pathway, membrane fusion and fission events take place at multiple steps. The regulator and effector molecules involved in uptake and transit are largely conserved between higher and lower eukaryotes. This feature, together with its accessibility by molecular genetics, recommend Dictyostelium as a valuable model system for mammalian cells.
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Affiliation(s)
- M Maniak
- Abt. Zellbiologie, Universität GhK, Heinrich-Plett-Str. 40, D-34132, Kassel, Germany.
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21
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Yuan A, Chia CP. Role of esterase gp70 and its influence on growth and development of Dictyostelium discoideum. Exp Cell Res 2000; 261:336-47. [PMID: 11112340 DOI: 10.1006/excr.2000.5055] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Gp70 is an esterase originally called crystal protein because of its presence in crystalline structures in aggregation-competent Dictyostelium discoideum cells. Although postulated to break down spore coats, the function of gp70 in vivo was incompletely investigated. Our immunolocalization and biochemical studies of vegetative D. discoideum amoebae show that gp70 was recruited to phagosomes and found in lysosomes. Purified gp70 was effective at hydrolyzing naphthyl substrates with acyl chains typical of lipids and lipopolysaccharides, indicating that the gp70 was involved in digesting endocytosed molecules. The activity of purified gp70 was inhibited by reductants that retarded its electrophoretic mobility and verified the presence of intramolecular disulfide bonds predicted by its amino acid sequence. Compared to wild-type cells, cells overexpressing gp70 were more phagocytically active, had shorter generation times, and produced more fruiting bodies per unit area, while cells lacking gp70 were phagocytically less active with longer doubling times, developed more slowly, and had significantly fewer fruiting bodies per unit area. Consistent with the phenotype of a disrupted metabolism, one-third of the gp70-minus cells were large and multinucleated. Together, these results indicated that despite its crystalline appearance, gp70 was an active esterase involved in both the growth and the development of D. discoideum.
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Affiliation(s)
- A Yuan
- School of Biological Sciences, University of Nebraska, Lincoln, Nebraska 68588-0118, USA.
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22
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Noegel AA, Schleicher M. The actin cytoskeleton of Dictyostelium: a story told by mutants. J Cell Sci 2000; 113 ( Pt 5):759-66. [PMID: 10671366 DOI: 10.1242/jcs.113.5.759] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Actin-binding proteins are effectors of cell signalling and coordinators of cellular behaviour. Research on the Dictyostelium actin cytoskeleton has focused both on the elucidation of the function of bona fide actin-binding proteins as well as on proteins involved in signalling to the cytoskeleton. A major part of this work is concerned with the analysis of Dictyostelium mutants. The results derived from these investigations have added to our understanding of the role of the actin cytoskeleton in growth and development. Furthermore, the studies have identified several cellular and developmental stages that are particularly sensitive to an unbalanced cytoskeleton. In addition, use of GFP fusion proteins is revealing the spatial and temporal dynamics of interactions between actin-associated proteins and the cytoskeleton.
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Affiliation(s)
- A A Noegel
- Institut für Biochemie I, Medizinische Fakultät, Universität zu Köln, Joseph-Stelzmann-Str. 52, Germany.
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23
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Ponte E, Rivero F, Fechheimer M, Noegel A, Bozzaro S. Severe developmental defects in Dictyostelium null mutants for actin-binding proteins. Mech Dev 2000; 91:153-61. [PMID: 10704840 DOI: 10.1016/s0925-4773(99)00292-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
The actin cytoskeleton is implicated in many cellular processes, such as cell adhesion, locomotion, contraction and cytokinesis, which are central to any development. The extent of polymerization, cross-linking, and bundling of actin is regulated by several actin-binding proteins. Knock-out mutations in these proteins have revealed in many cases only subtle, if any, defects in development, suggesting that the actin system is redundant, with multiple proteins sharing overlapping functions. The apparent redundancy may, however, reflect limitations of available laboratory assays in assessing the developmental role of a given protein. By using a novel assay, which reproduces conditions closer to the natural ones, we have re-examined the effects of disruption of many actin-binding proteins, and show here that deletion of alpha-actinin, interaptin, synexin, 34-kDa actin-bundling protein, and gelation factor affect to varying degrees the efficiency of Dictyostelium cells to complete development and form viable spores. No phenotypic defects were found in hisactophilin or comitin null mutants.
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Affiliation(s)
- E Ponte
- Dipartimento di Scienze Cliniche e Biologiche, Università di Torino, Ospedale S. Luigi, 10043-, Orbassano, Italy
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24
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Abstract
The actin cytoskeleton is an essential structure for most movements at the cellular and intracellular level. Whereas for contraction a muscle cell requires a rather static organisation of cytoskeletal proteins, cell motility of amoeboid cells relies on a tremendously dynamic turnover of filamentous networks in a matter of seconds and at distinct regions inside the cell. The best model system for studying cell motility is Dictyostelium discoideum. The cells live as single amoebae but can also start a developmental program that leads to multicellular stages and differentiation into simple types of tissues. Thus, cell motility can be studied on single cells and on cells in a tissue-like aggregate. The ability to combine protein purification and biochemistry with fairly easy molecular genetics is a unique feature for investigation of the cytoskeleton and cell motility. The actin cytoskeleton in Dictyostelium harbours essentially all classes of actin-binding proteins that have been found throughout eukaryotes. By conventional mutagenesis, gene disruption, antisense approaches, or gene replacements many genes that code for cytoskeletal proteins have been disrupted, and altered phenotypes in transformants that lacked one or more of those cytoskeletal proteins allowed solid conclusions about their in vivo function. In addition, tagging the proteins or selected domains with green fluorescent protein allows the monitoring of protein redistribution during cell movement. Gene tagging by restriction enzyme mediated integration of vectors and the ongoing international genome and cDNA sequencing projects offer the chance to understand the dynamics of the cytoskeleton by identification and functional characterisation of all proteins involved.
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Affiliation(s)
- L Eichinger
- Adolf-Butenandt-Institut/Zellbiologie, Ludwig-Maximilians-Universität, 80336 München, Germany.
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