1
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Chou SZ, Pollard TD. Cryo-electron microscopy structures of pyrene-labeled ADP-P i- and ADP-actin filaments. Nat Commun 2020; 11:5897. [PMID: 33214556 PMCID: PMC7677365 DOI: 10.1038/s41467-020-19762-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Accepted: 10/28/2020] [Indexed: 11/17/2022] Open
Abstract
Since the fluorescent reagent N-(1-pyrene)iodoacetamide was first used to label skeletal muscle actin in 1981, the pyrene-labeled actin has become the most widely employed tool to measure the kinetics of actin polymerization and the interaction between actin and actin-binding proteins. Here we report high-resolution cryo-electron microscopy structures of actin filaments with N-1-pyrene conjugated to cysteine 374 and either ADP (3.2 Å) or ADP-phosphate (3.0 Å) in the active site. Polymerization buries pyrene in a hydrophobic cavity between subunits along the long-pitch helix with only minor differences in conformation compared with native actin filaments. These structures explain how polymerization increases the fluorescence 20-fold, how myosin and cofilin binding to filaments reduces the fluorescence, and how profilin binding to actin monomers increases the fluorescence. For almost forty years, N-(1-pyrene) iodoacetamide has been used to label actin at C374, but the mechanisms of the fluorescence changes are still unknown due to the lack of structural information. Here authors provide cryo-EM structures of actin filaments with N-1-pyrene conjugated to cysteine 374 and either ADP or ADP-phosphate in the active site.
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Affiliation(s)
- Steven Z Chou
- Department of Molecular Cellular and Developmental Biology, Yale University, PO Box 208103, New Haven, CT, 06520-8103, USA
| | - Thomas D Pollard
- Department of Molecular Cellular and Developmental Biology, Yale University, PO Box 208103, New Haven, CT, 06520-8103, USA. .,Department of Molecular Biophysics and Biochemistry, Yale University, PO Box 208103, New Haven, CT, 06520-8103, USA. .,Department of Cell Biology, Yale University, PO Box 208103, New Haven, CT, 06520-8103, USA.
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2
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Kumpula EP, Pires I, Lasiwa D, Piirainen H, Bergmann U, Vahokoski J, Kursula I. Apicomplexan actin polymerization depends on nucleation. Sci Rep 2017; 7:12137. [PMID: 28939886 PMCID: PMC5610305 DOI: 10.1038/s41598-017-11330-w] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Accepted: 08/22/2017] [Indexed: 01/21/2023] Open
Abstract
Filamentous actin is critical for apicomplexan motility and host cell invasion. Yet, parasite actin filaments are short and unstable. Their kinetic characterization has been hampered by the lack of robust quantitative methods. Using a modified labeling method, we carried out thorough biochemical characterization of malaria parasite actin. In contrast to the isodesmic polymerization mechanism suggested for Toxoplasma gondii actin, Plasmodium falciparum actin I polymerizes via the classical nucleation-elongation pathway, with kinetics similar to canonical actins. A high fragmentation rate, governed by weak lateral contacts within the filament, is likely the main reason for the short filament length. At steady state, Plasmodium actin is present in equal amounts of short filaments and dimers, with a small proportion of monomers, representing the apparent critical concentration of ~0.1 µM. The dimers polymerize but do not serve as nuclei. Our work enhances understanding of actin evolution and the mechanistic details of parasite motility, serving as a basis for exploring parasite actin and actin nucleators as drug targets against malaria and other apicomplexan parasitic diseases.
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Affiliation(s)
- Esa-Pekka Kumpula
- Biocenter Oulu and Faculty of Biochemistry and Molecular Medicine, University of Oulu, Aapistie 7, 90220, Oulu, Finland
| | - Isa Pires
- Biocenter Oulu and Faculty of Biochemistry and Molecular Medicine, University of Oulu, Aapistie 7, 90220, Oulu, Finland
| | - Devaki Lasiwa
- Biocenter Oulu and Faculty of Biochemistry and Molecular Medicine, University of Oulu, Aapistie 7, 90220, Oulu, Finland
| | - Henni Piirainen
- Biocenter Oulu and Faculty of Biochemistry and Molecular Medicine, University of Oulu, Aapistie 7, 90220, Oulu, Finland
| | - Ulrich Bergmann
- Biocenter Oulu and Faculty of Biochemistry and Molecular Medicine, University of Oulu, Aapistie 7, 90220, Oulu, Finland
| | - Juha Vahokoski
- Biocenter Oulu and Faculty of Biochemistry and Molecular Medicine, University of Oulu, Aapistie 7, 90220, Oulu, Finland.,Department of Biomedicine, University of Bergen, Jonas Lies vei 91, 5009, Bergen, Norway
| | - Inari Kursula
- Biocenter Oulu and Faculty of Biochemistry and Molecular Medicine, University of Oulu, Aapistie 7, 90220, Oulu, Finland. .,Department of Biomedicine, University of Bergen, Jonas Lies vei 91, 5009, Bergen, Norway.
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3
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Sklyarova T, De Corte V, Meerschaert K, Devriendt L, Vanloo B, Bailey J, Cook LJ, Goethals M, Van Damme J, Puype M, Vandekerckhove J, Gettemans J. Fragmin60 encodes an actin-binding protein with a C2 domain and controls actin Thr-203 phosphorylation in Physarum plasmodia and sclerotia. J Biol Chem 2002; 277:39840-9. [PMID: 12167630 DOI: 10.1074/jbc.m207052200] [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: 11/06/2022] Open
Abstract
We report the isolation of a cDNA clone encoding a 60-kDa protein termed fragmin60 that cross-reacts with fragmin antibodies. Unlike other gelsolin-related proteins, fragmin60 contains a unique N-terminal domain that shows similarity with C2 domains of aczonin, protein kinase C, and synaptotagmins. The fragmin60 C2 domain binds three calcium ions, one with nanomolar affinity and two with micromolar affinity. Actin binding by fragmin60 requires higher calcium concentrations than does binding of actin by a fragmin60 mutant lacking the C2 domain, suggesting that the C2 domain secures the actin binding moiety in a conformation preventing actin binding at low calcium concentrations. The fragmin60 C2 domain does not bind phospholipids but interacts with the endogenous homologue of Saccharomyces cerevisiae S-phase kinase-associated protein (Skp1), as shown by pull-down assays and co-expression in mammalian cells. Recombinant fragmin60 promotes in vitro phosphorylation of actin Thr-203 by the actin-fragmin kinase. We further show that in vivo phosphorylation of actin in the fragmin60-actin complex occurs in sclerotia, a dormant stage of Physarum development, as well as in plasmodia. Our findings indicate that we have cloned a novel type of gelsolin-related actin-binding protein that is involved in controlling regulation of actin phosphorylation in vivo.
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Affiliation(s)
- Tatyana Sklyarova
- Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University, Rommelaere Institute, Albert Baertsoenkaai 3, B-9000 Ghent, Belgium
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4
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Murray JW, Edmonds BT, Liu G, Condeelis J. Bundling of actin filaments by elongation factor 1 alpha inhibits polymerization at filament ends. J Cell Biol 1996; 135:1309-21. [PMID: 8947553 PMCID: PMC2121097 DOI: 10.1083/jcb.135.5.1309] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Elongation factor 1 alpha (EF1 alpha) is an abundant protein that binds aminoacyl-tRNA and ribosomes in a GTP-dependent manner. EF1 alpha also interacts with the cytoskeleton by binding and bundling actin filaments and microtubules. In this report, the effect of purified EF1 alpha on actin polymerization and depolymerization is examined. At molar ratios present in the cytosol, EF1 alpha significantly blocks both polymerization and depolymerization of actin filaments and increases the final extent of actin polymer, while at high molar ratios to actin, EF1 alpha nucleates actin polymerization. Although EF1 alpha binds actin monomer, this monomer-binding activity does not explain the effects of EF1 alpha on actin polymerization at physiological molar ratios. The mechanism for the inhibition of polymerization is related to the actin-bundling activity of EF1 alpha. Both ends of the actin filament are inhibited for polymerization and both bundling and the inhibition of actin polymerization are affected by pH within the same physiological range; at high pH both bundling and the inhibition of actin polymerization are reduced. Additionally, it is seen that the binding of aminoacyl-tRNA to EF1 alpha releases EF1 alpha's inhibiting effect on actin polymerization. These data demonstrate that EF1 alpha can alter the assembly of F-actin, a filamentous scaffold on which non-membrane-associated protein translation may be occurring in vivo.
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Affiliation(s)
- J W Murray
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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5
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Gottwald U, Brokamp R, Karakesisoglou I, Schleicher M, Noegel AA. Identification of a cyclase-associated protein (CAP) homologue in Dictyostelium discoideum and characterization of its interaction with actin. Mol Biol Cell 1996; 7:261-72. [PMID: 8688557 PMCID: PMC275878 DOI: 10.1091/mbc.7.2.261] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
In search for novel actin binding proteins in Dictyostelium discoideum we have isolated a cDNA clone coding for a protein of approximately 50 kDa that is highly homologous to the class of adenylyl cyclase-associated proteins (CAP). In Saccharomyces cerevisiae the amino-terminal part of CAP is involved in the regulation of the adenylyl cyclase whereas the loss of the carboxyl-terminal domain results in morphological and nutritional defects. To study the interaction of Dictyostelium CAP with actin, the complete protein and its amino-terminal and carboxyl-terminal domains were expressed in Escherichia coli and used in actin binding assays. CAP sequestered actin in a Ca2+ independent way. This activity was localized to the carboxyl-terminal domain. CAP and its carboxyl-terminal domain led to a fluorescence enhancement of pyrene-labeled G-actin up to 50% indicating a direct interaction, whereas the amino-terminal domain did not enhance. In polymerization as well as in viscometric assays the ability of the carboxyl-terminal domain to sequester actin and to prevent F-actin formation was approximately two times higher than that of intact CAP. The sequestering activity of full length CAP could be inhibited by phosphatidylinositol 4,5-bisphosphate (PIP2), whereas the activity of the carboxyl-terminal domain alone was not influenced, suggesting that the amino-terminal half of the protein is required for the PIP2 modulation of the CAP function. In profilin-minus cells the CAP concentration is increased by approximately 73%, indicating that CAP may compensate some profilin functions in vivo. In migrating D. discoideum cells CAP was enriched at anterior and posterior plasma membrane regions. Only a weak staining of the cytoplasm was observed. In chemotactically stimulated cells the protein was very prominent in leading fronts. The data suggest an involvement of D. discoideum CAP in microfilament reorganization near the plasma membrane in a PIP2-regulated manner.
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Affiliation(s)
- U Gottwald
- Max-Planck-Institut für Biochemie, Martinsried, Germany
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6
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Milzani A, DalleDonne I, Colombo R. N-ethylmaleimide-modified actin filaments do not bundle in the presence of alpha-actinin. Biochem Cell Biol 1995; 73:116-22. [PMID: 7662311 DOI: 10.1139/o95-014] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
We show that the modification of actin subdomain 1 by N-ethylmaleimide (NEM), which binds Cys-374 close to the C-terminus of the molecule, inhibits the alpha-actinin-induced bundling of actin filaments. This effect is not merely related to the block of Cys-374, since N-(1-pyrenyl)iodoacetamide (pyrene-IA) is unable to prevent bundling. Considering that NEM (but not pyrene-IA) influences actin assembly, we suggest that the inhibition of the actin-alpha-actinin interaction is due to the chemical modification of actin Cys-374 which, by inducing a marked spatial reorganization of actin monomers, is able to modify both the intra- and inter-molecular interactions of this protein. Finally, NEM-modified actin filaments form bundles in the presence of polyethylene glycol 6000 since, in this case, the side by side association of actin filaments does not depend on the accessibility of binding sites nor on the formation of chemical bonds.
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Affiliation(s)
- A Milzani
- University of Milan, Dept. of Biology, Milan, Italy
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7
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Van Etten RA, Jackson PK, Baltimore D, Sanders MC, Matsudaira PT, Janmey PA. The COOH terminus of the c-Abl tyrosine kinase contains distinct F- and G-actin binding domains with bundling activity. J Cell Biol 1994; 124:325-40. [PMID: 8294516 PMCID: PMC2119935 DOI: 10.1083/jcb.124.3.325] [Citation(s) in RCA: 233] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The myristoylated form of c-Abl protein, as well as the P210bcr/abl protein, have been shown by indirect immunofluorescence to associate with F-actin stress fibers in fibroblasts. Analysis of deletion mutants of c-Abl stably expressed in fibroblasts maps the domain responsible for this interaction to the extreme COOH-terminus of Abl. This domain mediates the association of a heterologous protein with F-actin filaments after microinjection into NIH 3T3 cells, and directly binds to F-actin in a cosedimentation assay. Microinjection and cosedimentation assays localize the actin-binding domain to a 58 amino acid region, including a charged motif at the extreme COOH-terminus that is important for efficient binding. F-actin binding by Abl is calcium independent, and Abl competes with gelsolin for binding to F-actin. In addition to the F-actin binding domain, the COOH-terminus of Abl contains a proline-rich region that mediates binding and sequestration of G-actin, and the Abl F- and G-actin binding domains cooperate to bundle F-actin filaments in vitro. The COOH terminus of Abl thus confers several novel localizing functions upon the protein, including actin binding, nuclear localization, and DNA binding. Abl may modify and receive signals from the F-actin cytoskeleton in vivo, and is an ideal candidate to mediate signal transduction from the cell surface and cytoskeleton to the nucleus.
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Affiliation(s)
- R A Van Etten
- Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115
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8
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Zechel K. The interaction of 6-propionyl-2-(NN-dimethyl)aminonaphthalene (PRODAN)-labelled actin with actin-binding proteins and drugs. Biochem J 1993; 290 ( Pt 2):411-7. [PMID: 8452529 PMCID: PMC1132289 DOI: 10.1042/bj2900411] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The influence of various actin-binding proteins and drugs on the fluorescence emission of rabbit muscle actin labelled with the fluorescent probe acrylodan (6-acryloyl-2-dimethylaminonaphthalene) at Cys-374, the penultimate amino acid residue of the actin amino acid sequence, was studied. Addition of myosin, tropomyosin or phalloidin, agents known to bind only to filamentous F-actin, did not change the emission energy or the integrated intensity of the fluorescence spectrum. The presence of heavy meromyosin or of the glycolytic enzyme aldolase led to a small (approx. 2%) increase in the integrated intensity, and in the energy of the emitted fluorescence. The interaction of 6-propionyl-2-(NN-dimethyl)aminonaphthalene (PRODAN)-F-actin with pancreatic DNAase I and with a filament-severing 19 kDa protein from pig brain resulted in the gradual reduction of the integrated intensity of the emission and a red shift of the emission energy, suggestive of a disintegration of the actin filament structure. Profilin caused a < 10% change in the emission energy. Cytochalasin D reduced the integrated intensity of PRODAN-F-actin and red-shifted the emission energy, while cytochalasin B was without influence. Pancreatic DNAase I did not change the fluorescence emission of PRODAN-G-actin, suggesting that binding of this enzyme does not alter the environment of the probe. When the 19 kDa protein bound to PRODAN-G-actin, however, the integrated intensity was reduced and the emission energy was lowered. This effect was exploited to estimate the binding constant for the interaction between the 19 kDa protein and PRODAN-G-actin. The Kd was found to be about 0.25 microM.
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Affiliation(s)
- K Zechel
- Max-Planck-Institut for Biophysical Chemistry, Department of Biochemistry, Göttingen, Federal Republic of Germany
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9
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Katakami Y, Katakami N, Janmey PA, Hartwig JH, Stossel TP. Isolation of the phosphatidylinositol 4-monophosphate dissociable high-affinity profilin-actin complex. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1122:123-35. [PMID: 1322701 DOI: 10.1016/0167-4838(92)90314-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Profilin was originally discovered in a tight complex with monomeric actin from bovine spleen, leading to its description as an actin monomer sequestering protein that maintains a pool of unpolymerized actin in cells. Subsequent purifications of profilin using different methods from diverse cells have consistently yielded preparations that affect the kinetics of actin assembly but do not efficiently maintain actin monomeric at steady state in solutions containing mM magnesium. Recent evidence that profilin inhibits phospholipase C and enhances nucleotide exchange of actin has led some to question whether profilin is ever truly an actin monomer sequestering agent. Here we report that the extraction of bovine spleen with fluoride- and pyrophosphate-containing solutions facilitates isolation of monomeric actin that is bound to profilin and does not polymerize in mM magnesium ion. The integrity of this complex depends on the presence of ATP. Phosphatidylinositol 4-monophosphate (PIP), previously shown to dissociate the low-affinity profilin-actin complex (Kd = 0.4 microM in mM Mg2+), also dissociates the high-affinity profilin-actin complex (Kd less than 0.02 microM in mM Mg2+) yielding actin that is polymerization competent and profilin that functions like profilins purified by conventional methods. Although the chemical basis of these results is not known, they indicate that profilin can tightly sequester actin monomers and support the earlier suggestion that the affinity of profilin for actin may be under metabolic control.
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Affiliation(s)
- Y Katakami
- Department of Medicine, Brigham and Women's Hospital, Boston, MA
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10
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Hofmann A, Eichinger L, André E, Rieger D, Schleicher M. Cap100, a novel phosphatidylinositol 4,5-bisphosphate-regulated protein that caps actin filaments but does not nucleate actin assembly. CELL MOTILITY AND THE CYTOSKELETON 1992; 23:133-44. [PMID: 1333365 DOI: 10.1002/cm.970230206] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The fast and transient polymerization of actin in nonmuscle cells after stimulation with chemoattractants requires strong nucleation activities but also components that inhibit this process in resting cells. In this paper, we describe the purification and characterization of a new actin-binding protein from Dictyostelium discoideum that exhibited strong F-actin capping activity but did not nucleate actin assembly independently of the Ca2+ concentration. These properties led at physiological salt conditions to an inhibition of actin polymerization at a molar ratio of capping protein to actin below 1:1,000. The protein is a monomer, with a molecular mass of approximately 100 kDa, and is present in growing and in developing amoebae. Based on its F-actin capping function and its apparent molecular weight, we designated this monomeric protein cap100. As shown by dilution-induced depolymerization and by elongation assays, cap100 capped the barbed ends of actin filaments and did not sever F-actin. In agreement with its capping activity, cap100 increased the critical concentration for actin polymerization. In excitation or emission scans of pyrene-labeled G-actin, the fluorescence was increased in the presence of cap100. This suggests a G-actin binding activity for cap100. The capping activity could be completely inhibited by phosphatidylinositol 4,5-bisphosphate (PIP2), and bound cap100 could be removed by PIP2. The inhibition by phosphatidylinositol and the Ca(2+)-independent down-regulation of spontaneous actin polymerization indicate that cap100 plays a role in balancing the G- and F-actin pools of a resting cell. In the cytoplasm, the equilibrium would be shifted towards G-actin, but, below the membrane where F-actin is required, this activity would be inhibited by PIP2.
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Affiliation(s)
- A Hofmann
- Max-Planck-Institute for Biochemistry, Martinsried, Federal Republic of Germany
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11
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Maciver SK, Zot HG, Pollard TD. Characterization of actin filament severing by actophorin from Acanthamoeba castellanii. J Cell Biol 1991; 115:1611-20. [PMID: 1757465 PMCID: PMC2289216 DOI: 10.1083/jcb.115.6.1611] [Citation(s) in RCA: 189] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Actophorin is an abundant 15-kD actinbinding protein from Acanthamoeba that is thought to form a nonpolymerizable complex with actin monomers and also to reduce the viscosity of polymerized actin by severing filaments (Cooper et al., 1986. J. Biol. Chem. 261:477-485). Homologous proteins have been identified in sea urchin, chicken, and mammalian tissues. Chemical crosslinking produces a 1:1 covalent complex of actin and actophorin. Actophorin and profilin compete for crosslinking to actin monomers. The influence of actophorin on the steady-state actin polymer concentration gave a Kd of 0.2 microM for the complex of actophorin with actin monomers. Several new lines of evidence, including assays for actin filament ends by elongation rate and depolymerization rate, show that actophorin severs actin filaments both at steady state and during spontaneous polymerization. This is confirmed by direct observation in the light microscope and by showing that the effects of actophorin on the low shear viscosity of polymerized actin cannot be explained by monomer sequestration. The severing activity of actophorin is strongly inhibited by stoichiometric concentrations of phalloidin or millimolar concentrations of inorganic phosphate.
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Affiliation(s)
- S K Maciver
- Department of Cell Biology and Anatomy, Johns Hopkins School of Medicine, Baltimore, Maryland 21205
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12
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Eichinger L, Noegel AA, Schleicher M. Domain structure in actin-binding proteins: expression and functional characterization of truncated severin. J Biophys Biochem Cytol 1991; 112:665-76. [PMID: 1847147 PMCID: PMC2288858 DOI: 10.1083/jcb.112.4.665] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Severin from Dictyostelium discoideum is a Ca2(+)-activated actin-binding protein that severs actin filaments, nucleates actin assembly, and caps the fast growing ends of actin filaments. Sequence comparison with functionally related proteins, such as gelsolin, villin, or fragmin revealed highly conserved domains which are thought to be of functional significance. To attribute the different activities of the severin molecule to defined regions, progressively truncated severin polypeptides were constructed. The complete cDNA coding for 362 (DS362) amino acids and five 3' deletions coding for 277 (DS277), 177 (DS177), 151 (DS151), 117 (DS117), or 111 (DS111) amino acids were expressed in Escherichia coli. The proteins were purified to homogeneity and then characterized with respect to their effects on the polymerization or depolymerization kinetics of G- or F-actin solutions and their binding to G-actin. Furthermore, the Ca2+ binding of these proteins was investigated with a 45Ca-overlay assay and by monitoring Ca2(+)-dependent changes in tryptophan fluorescence. Bacterially expressed DS362 showed the same Ca2(+)-dependent activities as native severin. DS277, missing the 85 COOH-terminal amino acids of severin, had lost its strict Ca2+ regulation and displayed a Ca2(+)-independent capping activity, but was still Ca2+ dependent in its severing and nucleating activities. DS151 which corresponded to the first domain of gelsolin or villin had completely lost severing and nucleating properties. However, a residual severing activity of approximately 2% was detectable if 26 amino acids more were present at the COOH-terminal end (DS177). This locates similar to gelsolin the second actin-binding site to the border region between the first and second domain. Measuring the fluorescence enhancement of pyrene-labeled G-actin in the presence of DS111 showed that the first actin-binding site was present in the NH2-terminal 111 amino acids. Extension by six or more amino acids stabilized this actin-binding site in such a way that DS117 and even more pronounced DS151 became Ca2(+)-independent capping proteins. In comparison to many reports on gelsolin we draw the following conclusions. Among the three active actin-binding sites in gelsolin the closely neighboured sites one and two share the F-actin fragmenting function, whereas the actin-binding sites two and three, which are located in far distant domains, collaborate for nucleation. In contrast, severin contains two active actin-binding sites which are next to each other and are responsible for the severing as well as the nucleating function. The single actin-binding site near the NH2-terminus is sufficient for capping of actin filaments.
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Affiliation(s)
- L Eichinger
- Max-Planck-Institute for Biochemistry, Martinsried, Federal Republic of Germany
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14
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Haarer BK, Lillie SH, Adams AE, Magdolen V, Bandlow W, Brown SS. Purification of profilin from Saccharomyces cerevisiae and analysis of profilin-deficient cells. J Cell Biol 1990; 110:105-14. [PMID: 2404021 PMCID: PMC2115986 DOI: 10.1083/jcb.110.1.105] [Citation(s) in RCA: 228] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
We have isolated profilin from yeast (Saccharomyces cerevisiae) and have microsequenced a portion of the protein to confirm its identity; the region microsequenced agrees with the predicted amino acid sequence from a profilin gene recently isolated from S. cerevisiae (Magdolen, V., U. Oechsner, G. Müller, and W. Bandlow. 1988. Mol. Cell. Biol. 8:5108-5115). Yeast profilin resembles profilins from other organisms in molecular mass and in the ability to bind to polyproline, retard the rate of actin polymerization, and inhibit hydrolysis of ATP by monomeric actin. Using strains that carry disruptions or deletions of the profilin gene, we have found that, under appropriate conditions, cells can survive without detectable profilin. Such cells grow slowly, are temperature sensitive, lose the normal ellipsoidal shape of yeast cells, often become multinucleate, and generally grow much larger than wild-type cells. In addition, these cells exhibit delocalized deposition of cell wall chitin and have dramatically altered actin distributions.
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Affiliation(s)
- B K Haarer
- Department of Anatomy and Cell Biology, University of Michigan Medical School, Ann Arbor 48109
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15
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Vandekerckhove JS, Kaiser DA, Pollard TD. Acanthamoeba actin and profilin can be cross-linked between glutamic acid 364 of actin and lysine 115 of profilin. J Cell Biol 1989; 109:619-26. [PMID: 2569469 PMCID: PMC2115722 DOI: 10.1083/jcb.109.2.619] [Citation(s) in RCA: 106] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Acanthamoeba profilin was cross-linked to actin via a zero-length isopeptide bond using carbodiimide. The covalently linked 1:1 complex was purified and treated with cyanogen bromide. This cleaves actin into small cyanogen bromide (CNBr) peptides and leaves the profilin intact owing to its lack of methionine. Profilin with one covalently attached actin CNBr peptide was purified by gel filtration followed by gel electrophoresis and electroblotting on polybase-coated glass-fiber membranes. Since the NH2 terminus of profilin is blocked, Edman degradation gave only the sequence of the conjugated actin CNBr fragment beginning with Trp-356. The profilin-actin CNBr peptide conjugate was digested further with trypsin and the cross-linked peptide identified by comparison with the tryptic peptide pattern obtained from carbodiimide-treated profilin. Amino-acid sequence analysis of the cross-linked tryptic peptides produced two residues at each cycle. Their order corresponds to actin starting at Trp-356 and profilin starting at Ala-94. From the absence of the phenylthiohydantoin-amino acid residues in specific cycles, we conclude that actin Glu-364 is linked to Lys-115 in profilin. Experiments with the isoforms of profilin I and profilin II gave identical results. The cross-linked region in profilin is homologous with sequences in the larger actin filament capping proteins fragmin and gelsolin.
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16
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Abstract
The electrophoretic mobility of fluorescently labeled G-actin in polyacrylamide gels under nondenaturing conditions is altered by the formation of complexes with actin-binding proteins. This effect offers a convenient method for detecting and quantitating such proteins in tissue fractions and for monitoring their purification. When followed by second-dimension electrophoresis in the presence of sodium dodecyl sulfate, the method also gives the apparent molecular weights of the actin-binding components and the stoichiometry of the complexes. The method has also been used to identify actin-binding fragments in digests of actin-binding proteins, to investigate the formation of multicomponent complexes, and to determine the calcium-sensitivity of complexes.
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Affiliation(s)
- D Safer
- Department of Anatomy, School of Medicine, University of Pennsylvania, Philadelphia 19104-6058
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