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Amy S Gladfelter - One of the best experts on this subject based on the ideXlab platform.
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an amphipathic helix enables Septins to sense micrometer scale membrane curvature
Journal of Cell Biology, 2019Co-Authors: Kevin S Cannon, Amy S Gladfelter, Benjamin L Woods, John M CrutchleyAbstract:Cell shape is well described by membrane curvature. Septins are filament-forming, GTP-binding proteins that assemble on positive, micrometer-scale curvatures. Here, we examine the molecular basis of curvature sensing by Septins. We show that differences in affinity and the number of binding sites drive curvature-specific adsorption of Septins. Moreover, we find Septin assembly onto curved membranes is cooperative and show that geometry influences higher-order arrangement of Septin filaments. Although Septins must form polymers to stay associated with membranes, Septin filaments do not have to span micrometers in length to sense curvature, as we find that single-Septin complexes have curvature-dependent association rates. We trace this ability to an amphipathic helix (AH) located on the C-terminus of Cdc12. The AH domain is necessary and sufficient for curvature sensing both in vitro and in vivo. These data show that curvature sensing by Septins operates at much smaller length scales than the micrometer curvatures being detected.
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Analysis of Septin Reorganization at Cytokinesis Using Polarized Fluorescence Microscopy
Frontiers Media S.A., 2017Co-Authors: Amy S Gladfelter, Molly Mcquilken, Shalin B Mehta, Amitabh Verma, Rudolf Oldenbourg, Maximilian S. JentzschAbstract:Septins are conserved filament-forming proteins that act in diverse cellular processes. They closely associate with membranes and, in some systems, components of the cytoskeleton. It is not well understood how filaments assemble into higher-order structures in vivo or how they are remodeled throughout the cell cycle. In the budding yeast S. cerevisiae, Septins are found through most of the cell cycle in an hourglass organization at the mother-bud neck until cytokinesis when the collar splits into two rings that disassemble prior to the next cell cycle. Experiments using polarized fluorescence microscopy have suggested that Septins are arranged in ordered, paired filaments in the hourglass and undergo a coordinated 90° reorientation during splitting at cytokinesis. This apparent reorganization could be due to two orthogonal populations of filaments disassembling and reassembling or being preferentially retained at cytokinesis. In support of this idea, we report a decrease in Septin concentration at the mother-bud neck during cytokinesis consistent with other reports and the timing of the decrease depends on known Septin regulators including the Gin4 kinase. We took a candidate-based approach to examine what factors control reorientation during splitting and used polarized fluorescence microscopy to screen mutant yeast strains deficient in Septin interacting proteins. Using this method, we have linked known Septin regulators to different aspects of the assembly, stability, and reorganization of Septin assemblies. The data support that ring splitting requires Gin4 activity and an anillin-like protein Bud4, and normal accumulation of Septins at the ring requires phosphorylation of Shs1. We found distinct regulatory requirements for Septin organization in the hourglass compared to split rings. We propose that Septin subpopulations can vary in their localization and assembly/disassembly behavior in a cell-cycle dependent manner at cytokinesis
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micron scale plasma membrane curvature is recognized by the Septin cytoskeleton
Journal of Cell Biology, 2016Co-Authors: Patricia Occhipinti, Amy S Gladfelter, Maximilian S. Jentzsch, Andrew A Bridges, Patrick W OakesAbstract:Cells change shape in response to diverse environmental and developmental conditions, creating topologies with micron-scale features. Although individual proteins can sense nanometer-scale membrane curvature, it is unclear if a cell could also use nanometer-scale components to sense micron-scale contours, such as the cytokinetic furrow and base of neuronal branches. Septins are filament-forming proteins that serve as signaling platforms and are frequently associated with areas of the plasma membrane where there is micron-scale curvature, including the cytokinetic furrow and the base of cell protrusions. We report here that fungal and human Septins are able to distinguish between different degrees of micron-scale curvature in cells. By preparing supported lipid bilayers on beads of different curvature, we reconstitute and measure the intrinsic Septin curvature preference. We conclude that micron-scale curvature recognition is a fundamental property of the Septin cytoskeleton that provides the cell with a mechanism to know its local shape.
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cellular requirements for the small molecule forchlorfenuron to stabilize the Septin cytoskeleton
Cytoskeleton, 2010Co-Authors: Bradley S Demay, Rebecca A Meseroll, Patricia Occhipinti, Amy S GladfelterAbstract:The Septins are filament-forming, GTP-binding proteins that are conserved from yeast to humans. Septins assemble into higher-order structures such as rings, bars, and gauzes with diverse functions including serving as membrane diffusion barriers and scaffolds for cell signaling. The basis for Septin filament polymerization and the rules governing Septin polymer dynamics are presently not well understood. Pharmacological agents are essential tools in studying such properties of the actin and microtubule cytoskeletons however there are only limited reports of a drug specific to the Septin cytoskeleton. Forchlorfenuron (FCF) is a synthetic plant cytokinin used in agriculture which has been shown to alter Septin organization in yeast and mammalian tissue culture cells. Here we assess cellular requirements and properties of Septin-based structures induced by FCF. Treatment of the filamentous fungus Ashbya gossypii with FCF leads to assembly of extensive Septin fibers throughout hyphae which is rapidly reversed upon removal of the drug. These fibers do not exchange or add Septin subunits after assembly, indicating that FCF suppresses normal Septin dynamics and stabilizes the polymers. While FCF-induced Septin fibers do not co-localize to actin or microtubules, a polarized F-actin cytoskeleton is likely required for the assembly of drug-induced Septin fibers. Thus, FCF is a potent inducer of Septin polymerization and acts as a reversible stabilizer of extended Septin polymers. This drug will be a powerful tool for studying mechanisms of Septin polymerization and function, particularly in cell types where molecular analyses are complicated by the presence of multiple isoforms and limited genetics. © 2010 Wiley-Liss, Inc.
Michelle Momany - One of the best experts on this subject based on the ideXlab platform.
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Septins coordinate cell wall integrity and lipid metabolism in a sphingolipid dependent process
Journal of Cell Science, 2021Co-Authors: Alexander Mela, Michelle MomanyAbstract:Septins colocalize with membrane sterol-rich regions and facilitate recruitment of cell wall synthases during wall remodeling. We show that null mutants missing an Aspergillus nidulans core Septin present in hexamers and octamers (ΔaspAcdc11, ΔaspBcdc3, or ΔaspCcdc12) are sensitive to multiple cell wall-disturbing agents that activate the cell wall integrity MAPK pathway. The null mutant missing the octamer-exclusive core Septin (ΔaspDcdc10) showed similar sensitivity, but only to a single cell wall-disturbing agent and the null mutant missing the noncore Septin (ΔaspE) showed very mild sensitivity to a different single agent. Core Septin mutants showed changes in wall polysaccharide composition and chitin synthase localization. Mutants missing any of the five Septins resisted ergosterol-disrupting agents. Hexamer mutants showed increased sensitivity to sphingolipid-disrupting agents. Core Septins mislocalized after treatment with sphingolipid-disrupting agents, but not after ergosterol-disrupting agents. Our data suggest that the core Septins are involved in cell wall integrity signaling; that all five Septins are involved in monitoring ergosterol metabolism; that the hexamer Septins are required for sphingolipid metabolism; and that Septins require sphingolipids to coordinate the cell wall integrity response.
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Septins coordinate cell wall integrity and lipid metabolism in a sphingolipid dependent process
bioRxiv, 2020Co-Authors: Alexander Mela, Michelle MomanyAbstract:During normal development and response to environmental stress, fungi must coordinate synthesis of the cell wall and plasma membrane. Septins, small cytoskeletal GTPases, colocalize with membrane sterol-rich regions and facilitate recruitment of cell wall synthases during dynamic wall remodeling. In this study we show that null mutants missing an Aspergillus nidulans core Septin present in hexamers and octamers (∆aspAcdc11, ∆aspBcdc3, or ∆aspCcdc12) are sensitive to multiple cell wall-disturbing agents known to activate the cell wall integrity MAPK pathway and that this sensitivity can be remediated by osmotic support. The null mutant missing the octamer-exclusive core Septin (∆aspDcdc10) showed similar osmotic-remedial sensitivity, but only to a single cell wall-disturbing agent and the null mutant missing the noncore Septin (∆aspE) showed very mild osmotic-remedial sensitivity to a different single agent. Representative core Septin null mutants showed changes in cell wall polysaccharide composition, organization, and chitin synthase localization. Double mutant analysis with ΔmpkA suggested core Septins interact with the cell wall integrity pathway. Null mutants missing any of the five Septins were resistant to ergosterol-disrupting agents. The ∆aspAcdc11, ∆aspBcdc3, and ∆aspCcdc12 mutants showed increased sensitivity to sphingolipid-disrupting agents that was remediated by addition of exogenous phytosphingosine. Representative core Septins were mislocalized after treatment with sphingolipid-disrupting agents, but not after treatment with ergosterol-disrupting agents. When challenged with both sphingolipid-disturbing and cell wall-disturbing agents in combination, remediation of the lipid defect restored proper growth to ∆aspAcdc11, ∆aspBcdc3, and ∆aspCcdc12, but remediation of the cell wall defect did not. Our data suggest that the core hexamer and octamer Septins are involved in cell wall integrity signaling with the noncore Septin playing a minor role; that all five Septins are involved in monitoring ergosterol metabolism; that the hexamer Septins are required for sphingolipid metabolism; and that Septins require sphingolipids to coordinate the cell wall integrity response.
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Diversity of opisthokont Septin proteins reveals structural constraints and conserved motifs
BMC Evolutionary Biology, 2019Co-Authors: Benjamin Auxier, Mary L Berbee, Michelle MomanyAbstract:Background Septins are cytoskeletal proteins important in cell division and in establishing and maintaining cell polarity. Although Septins are found in various eukaryotes, Septin genes had the richest history of duplication and diversification in the animals, fungi and protists that comprise opisthokonts. Opisthokont Septin paralogs encode modular proteins that assemble into heteropolymeric higher order structures. The heteropolymers can create physical barriers to diffusion or serve as scaffolds organizing other morphogenetic proteins. How the paralogous Septin modules interact to form heteropolymers is still unclear. Through comparative analyses, we hoped to clarify the evolutionary origin of Septin diversity and to suggest which amino acid residues were responsible for subunit binding specificity. Results Here we take advantage of newly sequenced genomes to reconcile Septin gene trees with a species phylogeny from 22 animals, fungi and protists. Our phylogenetic analysis divided 120 Septins representing the 22 taxa into seven clades (Groups) of paralogs. Suggesting that Septin genes duplicated early in opisthokont evolution, animal and fungal lineages share Septin Groups 1A, 4 and possibly also 1B and 2. Group 5 Septins were present in fungi but not in animals and whether they were present in the opisthokont ancestor was unclear. Protein homology folding showed that previously identified conserved Septin motifs were all located near interface regions between the adjacent Septin monomers. We found specific interface residues associated with each Septin Group that are candidates for providing subunit binding specificity. Conclusions This work reveals that duplication of Septin genes began in an ancestral opisthokont more than a billion years ago and continued through the diversification of animals and fungi. Evidence for evolutionary conservation of ~ 49 interface residues will inform mutagenesis experiments and lead to improved understanding of the rules guiding Septin heteropolymer formation and from there, to improved understanding of development of form in animals and fungi.
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Additional file 2: of Diversity of opisthokont Septin proteins reveals structural constraints and conserved motifs
2019Co-Authors: Benjamin Auxier, Mary L Berbee, Jaclyn Dee, Michelle MomanyAbstract:Figure S1. Maximum likelihood phylogenetic analysis with RAxML software. Node values represent bootstrap support. Protein names are given for Septins supported by experimental evidence. Aspergillus and Drosophila sequences used to recognize Septin groups are in bold. Coiled-coil domain predictions, black representing p
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distinct Septin heteropolymers co exist during multicellular development in the filamentous fungus aspergillus nidulans
PLOS ONE, 2014Co-Authors: Yainitza Hernandezrodriguez, Shunsuke Masuo, Darryl Johnson, Ron Orlando, Amy Smith, Mara Coutorodriguez, Michelle MomanyAbstract:Septins are important components of the cytoskeleton that are highly conserved in eukaryotes and play major roles in cytokinesis, patterning, and many developmental processes. Septins form heteropolymers which assemble into higher-order structures including rings, filaments, and gauzes. In contrast to actin filaments and microtubules, the molecular mechanism by which Septins assemble is not well-understood. Here, we report that in the filamentous fungus Aspergillus nidulans, four core Septins form heteropolymeric complexes. AspE, a fifth Septin lacking in unicellular yeasts, interacts with only one of the core Septins, and only during multicellular growth. AspE is required for proper localization of three of the core Septins, and requires this same subset of core Septins for its own unique cortical localization. The ΔaspE mutant lacks developmentally-specific Septin higher-order structures and shows reduced spore production and slow growth with low temperatures and osmotic stress. Our results show that at least two distinct Septin heteropolymer populations co-exist in A. nidulans, and that while AspE is not a subunit of either heteropolymer, it is required for assembly of Septin higher-order structures found in multicellular development.
Yasin F. Dagdas - One of the best experts on this subject based on the ideXlab platform.
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Septin mediated plant cell invasion by the rice blast fungus magnaporthe oryzae
Science, 2012Co-Authors: Yasin F. Dagdas, Kae Yoshino, Gulay Dagdas, Lauren S Ryder, Ewa Bielska, Gero Steinberg, Nicholas J TalbotAbstract:To cause rice blast disease, the fungus Magnaporthe oryzae develops a pressurized dome-shaped cell called an appressorium, which physically ruptures the leaf cuticle to gain entry to plant tissue. Here, we report that a toroidal F-actin network assembles in the appressorium by means of four Septin guanosine triphosphatases, which polymerize into a dynamic, hetero-oligomeric ring. Septins scaffold F-actin, via the ezrin-radixin-moesin protein Tea1, and phosphatidylinositide interactions at the appressorium plasma membrane. The Septin ring assembles in a Cdc42- and Chm1-dependent manner and forms a diffusion barrier to localize the inverse-bin-amphiphysin-RVS–domain protein Rvs167 and the Wiskott-Aldrich syndrome protein Las17 at the point of penetration. Septins thereby provide the cortical rigidity and membrane curvature necessary for protrusion of a rigid penetration peg to breach the leaf surface.
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Spatial Uncoupling of Mitosis and Cytokinesis during Appressorium-Mediated Plant Infection by the Rice Blast Fungus Magnaporthe oryzae
The Plant cell, 2010Co-Authors: Diane G. O. Saunders, Yasin F. DagdasAbstract:To infect plants, many pathogenic fungi develop specialized infection structures called appressoria. Here, we report that appressorium development in the rice blast fungus Magnaporthe oryzae involves an unusual cell division, in which nuclear division is spatially uncoupled from the site of cytokinesis and septum formation. The position of the appressorium septum is defined prior to mitosis by formation of a heteromeric Septin ring complex, which was visualized by spatial localization of Septin4:green fluorescent protein (GFP) and Septin5:GFP fusion proteins. Mitosis in the fungal germ tube is followed by long-distance nuclear migration and rapid formation of an actomyosin contractile ring in the neck of the developing appressorium, at a position previously marked by the Septin complex. By contrast, mutants impaired in appressorium development, such as Deltapmk1 and DeltacpkA regulatory mutants, undergo coupled mitosis and cytokinesis within the germ tube. Perturbation of the spatial control of septation, by conditional mutation of the SEPTATION-ASSOCIATED1 gene of M. oryzae, prevented the fungus from causing rice blast disease. Overexpression of SEP1 did not affect septation during appressorium formation, but instead led to decoupling of nuclear division and cytokinesis in nongerminated conidial cells. When considered together, these results indicate that SEP1 is essential for determining the position and frequency of cell division sites in M. oryzae and demonstrate that differentiation of appressoria requires a cytokinetic event that is distinct from cell divisions within hyphae.
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spatial uncoupling of mitosis and cytokinesis during appressorium mediated plant infection by the rice blast fungus magnaporthe oryzae
The Plant Cell, 2010Co-Authors: Diane G. O. Saunders, Yasin F. Dagdas, Nicholas J TalbotAbstract:To infect plants, many pathogenic fungi develop specialized infection structures called appressoria. Here, we report that appressorium development in the rice blast fungus Magnaporthe oryzae involves an unusual cell division, in which nuclear division is spatially uncoupled from the site of cytokinesis and septum formation. The position of the appressorium septum is defined prior to mitosis by formation of a heteromeric Septin ring complex, which was visualized by spatial localization of Septin4:green fluorescent protein (GFP) and Septin5:GFP fusion proteins. Mitosis in the fungal germ tube is followed by long-distance nuclear migration and rapid formation of an actomyosin contractile ring in the neck of the developing appressorium, at a position previously marked by the Septin complex. By contrast, mutants impaired in appressorium development, such as Δpmk1 and ΔcpkA regulatory mutants, undergo coupled mitosis and cytokinesis within the germ tube. Perturbation of the spatial control of septation, by conditional mutation of the SEPTATION-ASSOCIATED1 gene of M. oryzae, prevented the fungus from causing rice blast disease. Overexpression of SEP1 did not affect septation during appressorium formation, but instead led to decoupling of nuclear division and cytokinesis in nongerminated conidial cells. When considered together, these results indicate that SEP1 is essential for determining the position and frequency of cell division sites in M. oryzae and demonstrate that differentiation of appressoria requires a cytokinetic event that is distinct from cell divisions within hyphae.
Elias T. Spiliotis - One of the best experts on this subject based on the ideXlab platform.
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Septins Recognize and Entrap Dividing Bacterial Cells for Delivery to Lysosomes
Cell Host and Microbe, 2018Co-Authors: Sina Krokowski, Elias T. Spiliotis, Dimitrios Angelis, Damián Lobato-márquez, Arnaud Chastanet, Pedro Matos Pereira, Dieter Galea, Gerald Larrouy-maumus, Ricardo Henriques, Rut Carballido-lopezAbstract:The cytoskeleton occupies a central role in cellular immunity by promoting bacterial sensing and antibacterial functions. Septins are cytoskeletal proteins implicated in various cellular processes, including cell division. Septins also assemble into cage-like structures that entrap cytosolic Shigella, yet how Septins recognize bacteria is poorly understood. Here, we discover that Septins are recruited to regions of micron-scale membrane curvature upon invasion and division by a variety of bacterial species. Cardiolipin, a curvature-specific phospholipid, promotes Septin recruitment to highly curved membranes of Shigella, and bacterial mutants lacking cardiolipin exhibit less Septin cage entrapment. Chemically inhibiting cell separation to prolong membrane curvature or reducing Shigella cell growth respectively increases and decreases Septin cage formation. Once formed, Septin cages inhibit Shigella cell division upon recruitment of autophagic and lysosomal machinery. Thus, recognition of dividing bacterial cells by the Septin cytoskeleton is a powerful mechanism to restrict the proliferation of intracellular bacterial pathogens.
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Septins promote macropinosome maturation and traffic to the lysosome by facilitating membrane fusion
Journal of Cell Biology, 2016Co-Authors: Lee Dolat, Elias T. SpiliotisAbstract:Macropinocytosis, the internalization of extracellular fluid and material by plasma membrane ruffles, is critical for antigen presentation, cell metabolism, and signaling. Macropinosomes mature through homotypic and heterotypic fusion with endosomes and ultimately merge with lysosomes. The molecular underpinnings of this clathrin-independent endocytic pathway are largely unknown. Here, we show that the filamentous Septin GTPases associate preferentially with maturing macropinosomes in a phosphatidylinositol 3,5-bisphosphate-dependent manner and localize to their contact/fusion sites with macropinosomes/endosomes. Septin knockdown results in large clusters of docked macropinosomes, which persist longer and exhibit fewer fusion events. Septin depletion and overexpression down-regulates and enhances, respectively, the delivery of fluid-phase cargo to lysosomes, without affecting Rab5 and Rab7 recruitment to macropinosomes/endosomes. In vitro reconstitution assays show that fusion of macropinosomes/endosomes is abrogated by Septin immunodepletion and function-blocking antibodies and is induced by recombinant Septins in the absence of cytosol and polymerized actin. Thus, Septins regulate fluid-phase cargo traffic to lysosomes by promoting macropinosome maturation and fusion with endosomes/lysosomes.
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In Silico Docking of Forchlorfenuron (FCF) to Septins Suggests that FCF Interferes with GTP Binding
2016Co-Authors: Dimitrios Angelis, Eva Karasmanis, Xiaobo Bai, Elias T. SpiliotisAbstract:Septins are GTP-binding proteins that form cytoskeleton-like filaments, which are essential for many functions in eukaryotic organisms. Small molecule compounds that disrupt Septin filament assembly are valuable tools for dissecting Septin functions with high temporal control. To date, forchlorfenuron (FCF) is the only compound known to affect Septin assembly and functions. FCF dampens the dynamics of Septin assembly inducing the formation of enlarged stable polymers, but the underlying mechanism of action is unknown. To investigate how FCF binds and affects Septins, we performed in silico simulations of FCF docking to all available crystal structures of Septins. Docking of FCF with SEPT2 and SEPT3 indicated that FCF interacts preferentially with the nucleotide-binding pockets of Septins. Strikingly, FCF is predicted to form hydrogen bonds with residues involved in GDP-binding, mimicking nucleotide binding. FCF docking with the structure of SEPT2-GppNHp, a nonhydrolyzable GTP analog, and SEPT7 showed that FCF may assume two alternative non-overlapping conformations deeply into and on the outer side of the nucleotide-binding pocket. Surprisingly, FCF was predicted to interact with the P-loop Walker A motif GxxxxGKS/T, which binds the phosphates of GTP, and the GTP specificity motif AKAD, which interacts with the guanine base of GTP, and highly conserved amino acids including a threonine, which is critical for GTP hydrolysis. Thus, in silico FCF exhibits a conserved mechanism of binding, interacting with Septin signature motifs and residues involved in GTP binding and hydrolysis. Taken together, our results suggest that FCF stabilizes Septin
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Septins promote stress fiber mediated maturation of focal adhesions and renal epithelial motility
Journal of Cell Biology, 2014Co-Authors: Lee Dolat, Vitold E Galkin, John L Hunyara, Jonathan R Bowen, Eva P Karasmanis, Maha Elgawly, Elias T. SpiliotisAbstract:Organogenesis and tumor metastasis involve the transformation of epithelia to highly motile mesenchymal-like cells. Septins are filamentous G proteins, which are overexpressed in metastatic carcinomas, but their functions in epithelial motility are unknown. Here, we show that a novel network of Septin filaments underlies the organization of the transverse arc and radial (dorsal) stress fibers at the leading lamella of migrating renal epithelia. Surprisingly, Septin depletion resulted in smaller and more transient and peripheral focal adhesions. This phenotype was accompanied by a highly disorganized lamellar actin network and rescued by the actin bundling protein α-actinin-1. We show that preassembled actin filaments are cross-linked directly by Septin 9 (SEPT9), whose expression is increased after induction of renal epithelial motility with the hepatocyte growth factor. Significantly, SEPT9 overexpression enhanced renal cell migration in 2D and 3D matrices, whereas SEPT9 knockdown decreased migration. These results suggest that Septins promote epithelial motility by reinforcing the cross-linking of lamellar stress fibers and the stability of nascent focal adhesions.
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in silico docking of forchlorfenuron fcf to Septins suggests that fcf interferes with gtp binding
PLOS ONE, 2014Co-Authors: Dimitrios Angelis, Eva Karasmanis, Elias T. SpiliotisAbstract:Septins are GTP-binding proteins that form cytoskeleton-like filaments, which are essential for many functions in eukaryotic organisms. Small molecule compounds that disrupt Septin filament assembly are valuable tools for dissecting Septin functions with high temporal control. To date, forchlorfenuron (FCF) is the only compound known to affect Septin assembly and functions. FCF dampens the dynamics of Septin assembly inducing the formation of enlarged stable polymers, but the underlying mechanism of action is unknown. To investigate how FCF binds and affects Septins, we performed in silico simulations of FCF docking to all available crystal structures of Septins. Docking of FCF with SEPT2 and SEPT3 indicated that FCF interacts preferentially with the nucleotide-binding pockets of Septins. Strikingly, FCF is predicted to form hydrogen bonds with residues involved in GDP-binding, mimicking nucleotide binding. FCF docking with the structure of SEPT2-GppNHp, a nonhydrolyzable GTP analog, and SEPT7 showed that FCF may assume two alternative non-overlapping conformations deeply into and on the outer side of the nucleotide-binding pocket. Surprisingly, FCF was predicted to interact with the P-loop Walker A motif GxxxxGKS/T, which binds the phosphates of GTP, and the GTP specificity motif AKAD, which interacts with the guanine base of GTP, and highly conserved amino acids including a threonine, which is critical for GTP hydrolysis. Thus, in silico FCF exhibits a conserved mechanism of binding, interacting with Septin signature motifs and residues involved in GTP binding and hydrolysis. Taken together, our results suggest that FCF stabilizes Septins by locking them into a conformation that mimics a nucleotide-bound state, preventing further GTP binding and hydrolysis. Overall, this study provides the first insight into how FCF may bind and stabilize Septins, and offers a blueprint for the rational design of FCF derivatives that could target Septins with higher affinity and specificity.
Nicholas J Talbot - One of the best experts on this subject based on the ideXlab platform.
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Septin mediated plant cell invasion by the rice blast fungus magnaporthe oryzae
Science, 2012Co-Authors: Yasin F. Dagdas, Kae Yoshino, Gulay Dagdas, Lauren S Ryder, Ewa Bielska, Gero Steinberg, Nicholas J TalbotAbstract:To cause rice blast disease, the fungus Magnaporthe oryzae develops a pressurized dome-shaped cell called an appressorium, which physically ruptures the leaf cuticle to gain entry to plant tissue. Here, we report that a toroidal F-actin network assembles in the appressorium by means of four Septin guanosine triphosphatases, which polymerize into a dynamic, hetero-oligomeric ring. Septins scaffold F-actin, via the ezrin-radixin-moesin protein Tea1, and phosphatidylinositide interactions at the appressorium plasma membrane. The Septin ring assembles in a Cdc42- and Chm1-dependent manner and forms a diffusion barrier to localize the inverse-bin-amphiphysin-RVS–domain protein Rvs167 and the Wiskott-Aldrich syndrome protein Las17 at the point of penetration. Septins thereby provide the cortical rigidity and membrane curvature necessary for protrusion of a rigid penetration peg to breach the leaf surface.
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spatial uncoupling of mitosis and cytokinesis during appressorium mediated plant infection by the rice blast fungus magnaporthe oryzae
The Plant Cell, 2010Co-Authors: Diane G. O. Saunders, Yasin F. Dagdas, Nicholas J TalbotAbstract:To infect plants, many pathogenic fungi develop specialized infection structures called appressoria. Here, we report that appressorium development in the rice blast fungus Magnaporthe oryzae involves an unusual cell division, in which nuclear division is spatially uncoupled from the site of cytokinesis and septum formation. The position of the appressorium septum is defined prior to mitosis by formation of a heteromeric Septin ring complex, which was visualized by spatial localization of Septin4:green fluorescent protein (GFP) and Septin5:GFP fusion proteins. Mitosis in the fungal germ tube is followed by long-distance nuclear migration and rapid formation of an actomyosin contractile ring in the neck of the developing appressorium, at a position previously marked by the Septin complex. By contrast, mutants impaired in appressorium development, such as Δpmk1 and ΔcpkA regulatory mutants, undergo coupled mitosis and cytokinesis within the germ tube. Perturbation of the spatial control of septation, by conditional mutation of the SEPTATION-ASSOCIATED1 gene of M. oryzae, prevented the fungus from causing rice blast disease. Overexpression of SEP1 did not affect septation during appressorium formation, but instead led to decoupling of nuclear division and cytokinesis in nongerminated conidial cells. When considered together, these results indicate that SEP1 is essential for determining the position and frequency of cell division sites in M. oryzae and demonstrate that differentiation of appressoria requires a cytokinetic event that is distinct from cell divisions within hyphae.