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Goode BL, Eskin J, Shekhar S. Mechanisms of actin disassembly and turnover. J Cell Biol 2023; 222:e202309021. [PMID: 37948068 PMCID: PMC10638096 DOI: 10.1083/jcb.202309021] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Revised: 10/21/2023] [Accepted: 10/23/2023] [Indexed: 11/12/2023] Open
Abstract
Cellular actin networks exhibit a wide range of sizes, shapes, and architectures tailored to their biological roles. Once assembled, these filamentous networks are either maintained in a state of polarized turnover or induced to undergo net disassembly. Further, the rates at which the networks are turned over and/or dismantled can vary greatly, from seconds to minutes to hours or even days. Here, we review the molecular machinery and mechanisms employed in cells to drive the disassembly and turnover of actin networks. In particular, we highlight recent discoveries showing that specific combinations of conserved actin disassembly-promoting proteins (cofilin, GMF, twinfilin, Srv2/CAP, coronin, AIP1, capping protein, and profilin) work in concert to debranch, sever, cap, and depolymerize actin filaments, and to recharge actin monomers for new rounds of assembly.
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Affiliation(s)
- Bruce L. Goode
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA, USA
| | - Julian Eskin
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA, USA
| | - Shashank Shekhar
- Departments of Physics, Cell Biology and Biochemistry, Emory University, Atlanta, GA, USA
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2
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Smith H, Pinkerton N, Heisler DB, Kudryashova E, Hall AR, Karch KR, Norris A, Wysocki V, Sotomayor M, Reisler E, Vavylonis D, Kudryashov DS. Rounding Out the Understanding of ACD Toxicity with the Discovery of Cyclic Forms of Actin Oligomers. Int J Mol Sci 2021; 22:E718. [PMID: 33450834 PMCID: PMC7828245 DOI: 10.3390/ijms22020718] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 12/30/2020] [Accepted: 01/09/2021] [Indexed: 11/17/2022] Open
Abstract
Actin is an essential element of both innate and adaptive immune systems and can aid in motility and translocation of bacterial pathogens, making it an attractive target for bacterial toxins. Pathogenic Vibrio and Aeromonas genera deliver actin cross-linking domain (ACD) toxin into the cytoplasm of the host cell to poison actin regulation and promptly induce cell rounding. At early stages of toxicity, ACD covalently cross-links actin monomers into oligomers (AOs) that bind through multivalent interactions and potently inhibit several families of actin assembly proteins. At advanced toxicity stages, we found that the terminal protomers of linear AOs can get linked together by ACD to produce cyclic AOs. When tested against formins and Ena/VASP, linear and cyclic AOs exhibit similar inhibitory potential, which for the cyclic AOs is reduced in the presence of profilin. In coarse-grained molecular dynamics simulations, profilin and WH2-motif binding sites on actin subunits remain exposed in modeled AOs of both geometries. We speculate, therefore, that the reduced toxicity of cyclic AOs is due to their reduced configurational entropy. A characteristic feature of cyclic AOs is that, in contrast to the linear forms, they cannot be straightened to form filaments (e.g., through stabilization by cofilin), which makes them less susceptible to neutralization by the host cell.
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Affiliation(s)
- Harper Smith
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (H.S.); (N.P.); (D.B.H.); (E.K.); (K.R.K.); (A.N.); (V.W.); (M.S.)
- Biophysics Graduate Program, The Ohio State University, Columbus, OH 43210, USA
| | - Nick Pinkerton
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (H.S.); (N.P.); (D.B.H.); (E.K.); (K.R.K.); (A.N.); (V.W.); (M.S.)
| | - David B. Heisler
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (H.S.); (N.P.); (D.B.H.); (E.K.); (K.R.K.); (A.N.); (V.W.); (M.S.)
- Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA
- Infectious Diseases Institute, The Ohio State University, Columbus, OH 43210, USA
| | - Elena Kudryashova
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (H.S.); (N.P.); (D.B.H.); (E.K.); (K.R.K.); (A.N.); (V.W.); (M.S.)
- Infectious Diseases Institute, The Ohio State University, Columbus, OH 43210, USA
| | - Aaron R. Hall
- Department of Physics, Lehigh University, Bethlehem, PA 18015, USA; (A.R.H.); (D.V.)
| | - Kelly R. Karch
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (H.S.); (N.P.); (D.B.H.); (E.K.); (K.R.K.); (A.N.); (V.W.); (M.S.)
| | - Andrew Norris
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (H.S.); (N.P.); (D.B.H.); (E.K.); (K.R.K.); (A.N.); (V.W.); (M.S.)
| | - Vicki Wysocki
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (H.S.); (N.P.); (D.B.H.); (E.K.); (K.R.K.); (A.N.); (V.W.); (M.S.)
| | - Marcos Sotomayor
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (H.S.); (N.P.); (D.B.H.); (E.K.); (K.R.K.); (A.N.); (V.W.); (M.S.)
- Biophysics Graduate Program, The Ohio State University, Columbus, OH 43210, USA
- Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA
| | - Emil Reisler
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA;
| | - Dimitrios Vavylonis
- Department of Physics, Lehigh University, Bethlehem, PA 18015, USA; (A.R.H.); (D.V.)
| | - Dmitri S. Kudryashov
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (H.S.); (N.P.); (D.B.H.); (E.K.); (K.R.K.); (A.N.); (V.W.); (M.S.)
- Biophysics Graduate Program, The Ohio State University, Columbus, OH 43210, USA
- Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA
- Infectious Diseases Institute, The Ohio State University, Columbus, OH 43210, USA
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Purde V, Kudryashova E, Heisler DB, Shakya R, Kudryashov DS. Intein-mediated cytoplasmic reconstitution of a split toxin enables selective cell ablation in mixed populations and tumor xenografts. Proc Natl Acad Sci U S A 2020; 117:22090-22100. [PMID: 32839344 PMCID: PMC7486740 DOI: 10.1073/pnas.2006603117] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The application of proteinaceous toxins for cell ablation is limited by their high on- and off-target toxicity, severe side effects, and a narrow therapeutic window. The selectivity of targeting can be improved by intein-based toxin reconstitution from two dysfunctional fragments provided their cytoplasmic delivery via independent, selective pathways. While the reconstitution of proteins from genetically encoded elements has been explored, exploiting cell-surface receptors for boosting selectivity has not been attained. We designed a robust splitting algorithm and achieved reliable cytoplasmic reconstitution of functional diphtheria toxin from engineered intein-flanked fragments upon receptor-mediated delivery of one of them to the cells expressing the counterpart. Retargeting the delivery machinery toward different receptors overexpressed in cancer cells enables selective ablation of specific subpopulations in mixed cell cultures. In a mouse model, the transmembrane delivery of a split-toxin construct potently inhibits the growth of xenograft tumors expressing the split counterpart. Receptor-mediated delivery of engineered split proteins provides a platform for precise therapeutic and experimental ablation of tumors or desired cell populations while also greatly expanding the applicability of the intein-based protein transsplicing.
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Affiliation(s)
- Vedud Purde
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210
- The Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210
| | - Elena Kudryashova
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210;
| | - David B Heisler
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210
- The Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210
| | - Reena Shakya
- Comprehensive Cancer Center, The Ohio State University, Columbus, OH 43210
| | - Dmitri S Kudryashov
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210;
- The Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210
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Actin Cross-Linking Toxin Is a Universal Inhibitor of Tandem-Organized and Oligomeric G-Actin Binding Proteins. Curr Biol 2018; 28:1536-1547.e9. [PMID: 29731300 DOI: 10.1016/j.cub.2018.03.065] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2017] [Revised: 03/06/2018] [Accepted: 03/28/2018] [Indexed: 11/20/2022]
Abstract
Delivery of bacterial toxins to host cells is hindered by host protective barriers. This obstruction dictates a remarkable efficiency of toxins, a single copy of which may kill a host cell. Efficiency of actin-targeting toxins is further hampered by an overwhelming abundance of their target. The actin cross-linking domain (ACD) toxins of Vibrio species and related bacterial genera catalyze the formation of covalently cross-linked actin oligomers. Recently, we reported that the ACD toxicity can be amplified via a multivalent inhibitory association of actin oligomers with actin assembly factors formins, suggesting that the oligomers may act as secondary toxins. Importantly, many proteins involved in nucleation, elongation, severing, branching, and bundling of actin filaments contain G-actin-binding Wiskott-Aldrich syndrome protein (WASP)-homology motifs 2 (WH2) organized in tandem and therefore may act as a multivalent platform for high-affinity interaction with the ACD-cross-linked actin oligomers. Using live-cell single-molecule speckle (SiMS) microscopy, total internal reflection fluorescence (TIRF) microscopy, and actin polymerization assays, we show that, in addition to formins, the oligomers bind with high affinity and potently inhibit several families of actin assembly factors: Ena/vasodilator-stimulated phosphorprotein (VASP); Spire; and the Arp2/3 complex, both in vitro and in live cells. As a result, ACD blocks the actin retrograde flow and membrane dynamics and disrupts association of Ena/VASP with adhesion complexes. This study defines ACD as a universal inhibitor of tandem-organized G-actin binding proteins that overcomes the abundance of actin by redirecting the toxicity cascade toward less abundant targets and thus leading to profound disorganization of the actin cytoskeleton and disruption of actin-dependent cellular functions.
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Woida PJ, Satchell KJF. Coordinated delivery and function of bacterial MARTX toxin effectors. Mol Microbiol 2017; 107:133-141. [PMID: 29114985 DOI: 10.1111/mmi.13875] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/04/2017] [Indexed: 12/22/2022]
Abstract
Bacteria often coordinate virulence factors to fine-tune the host response during infection. These coordinated events can include toxins counteracting or amplifying effects of another toxin or though regulating the stability of virulence factors to remove their function once it is no longer needed. Multifunctional autoprocessing repeats-in toxin (MARTX) toxins are effector delivery toxins that form a pore into the plasma membrane of a eukaryotic cell to deliver multiple effector proteins into the cytosol of the target cell. The function of these proteins includes manipulating actin cytoskeletal dynamics, regulating signal transduction pathways and inhibiting host secretory pathways. Investigations into the molecular mechanisms of these effector domains are providing insight into how the function of some effectors overlap and regulate one another during infection. Coordinated crosstalk of effector function suggests that MARTX toxins are not simply a sum of all their parts. Instead, modulation of cell function by effector domains may depend on which other effector domain are co-delivered. Future studies will elucidate how these effectors interact with each other to modulate the bacterial host interaction.
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Affiliation(s)
- Patrick J Woida
- Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Karla J F Satchell
- Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
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Aktories K, Schwan C, Lang AE. ADP-Ribosylation and Cross-Linking of Actin by Bacterial Protein Toxins. Handb Exp Pharmacol 2017; 235:179-206. [PMID: 27316913 DOI: 10.1007/164_2016_26] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Actin and the actin cytoskeleton play fundamental roles in host-pathogen interactions. Proper function of the actin cytoskeleton is crucial for innate and acquired immune defense. Bacterial toxins attack the actin cytoskeleton by targeting regulators of actin. Moreover, actin is directly modified by various bacterial protein toxins and effectors, which cause ADP-ribosylation or cross-linking of actin. Modification of actin can result in inhibition or stimulation of actin polymerization. Toxins, acting directly on actin, are reviewed.
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Affiliation(s)
- Klaus Aktories
- Institute for Experimental and Clinical Pharmacology and Toxicology, Albert-Ludwigs-Universität Freiburg, Freiburg, 79104, Germany. .,Freiburg Institute of Advanced Studies (FRIAS), Albert-Ludwigs-Universität Freiburg, Freiburg, 79104, Germany.
| | - Carsten Schwan
- Institute for Experimental and Clinical Pharmacology and Toxicology, Albert-Ludwigs-Universität Freiburg, Freiburg, 79104, Germany
| | - Alexander E Lang
- Institute for Experimental and Clinical Pharmacology and Toxicology, Albert-Ludwigs-Universität Freiburg, Freiburg, 79104, Germany
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Abstract
Multifunctional-autoprocessing repeats-in-toxin (MARTX) toxins are a heterogeneous group of toxins found in a number of Vibrio species and other Gram-negative bacteria. The toxins are composed of conserved repeat regions and an autoprocessing protease domain that together function as a delivery platform for transfer of cytotoxic and cytopathic domains into target eukaryotic cell cytosol. Within the cells, the effectors can alter biological processes such as signaling or cytoskeletal structure, presumably to the benefit of the bacterium. Ten effector domains are found in the various Vibrio MARTX toxins, although any one toxin carries only two to five effector domains. The specific toxin variant expressed by a species can be modified by homologous recombination to acquire or lose effector domains, such that different strains within the same species can express distinct variants of the toxins. This review examines the conserved structural elements of the MARTX toxins and details the different toxin arrangements carried by Vibrio species and strains. The catalytic function of domains and how the toxins are linked to pathogenesis of human and animals is described.
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Pathogenic Mechanisms of Actin Cross-Linking Toxins: Peeling Away the Layers. Curr Top Microbiol Immunol 2016; 399:87-112. [PMID: 27858184 DOI: 10.1007/82_2016_22] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Actin cross-linking toxins are produced by Gram-negative bacteria from Vibrio and Aeromonas genera. The toxins were named actin cross-linking domains (ACD), since the first and most of the subsequently discovered ACDs were found as effector domains in larger MARTX and VgrG toxins. Among recognized human pathogens, ACD is produced by Vibrio cholerae, Vibrio vulnificus, and Aeromonas hydrophila. Upon delivery to the cytoplasm of a host cell, ACD covalently cross-links actin monomers into non-polymerizable actin oligomers of various lengths. Provided sufficient doses of toxin are delivered, most or all actin can be promptly cross-linked into non-functional oligomers, leading to cell rounding, detachment from the substrate and, in many cases, cell death. Recently, a deeper layer of ACD toxicity with a less obvious but more potent mechanism was discovered. According to this finding, low doses of the ACD-produced actin oligomers can actively disrupt the actin cytoskeleton by potently inhibiting essential actin assembly proteins, formins. The first layer of toxicity is direct (as actin is the immediate and the only target), passive (since ACD-cross-linked actin oligomers are toxic only because they are non-functional), and less potent (as bulk quantities of one of the most abundant cytoplasmic proteins, actin, have to be modified). The second mechanism is indirect (as major targets, formins, are not affected by ACD directly), active (because actin oligomers act as "secondary" toxins), and highly potent [as it affects scarce and essential actin-binding proteins (ABPs)].
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Belyy A, Tabakova I, Lang AE, Jank T, Belyi Y, Aktories K. Roles of Asp179 and Glu270 in ADP-Ribosylation of Actin by Clostridium perfringens Iota Toxin. PLoS One 2015; 10:e0145708. [PMID: 26713879 PMCID: PMC4699905 DOI: 10.1371/journal.pone.0145708] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2015] [Accepted: 12/08/2015] [Indexed: 12/19/2022] Open
Abstract
Clostridium perfringens iota toxin is a binary toxin composed of the enzymatically active component Ia and receptor binding component Ib. Ia is an ADP-ribosyltransferase, which modifies Arg177 of actin. The previously determined crystal structure of the actin-Ia complex suggested involvement of Asp179 of actin in the ADP-ribosylation reaction. To gain more insights into the structural requirements of actin to serve as a substrate for toxin-catalyzed ADP-ribosylation, we engineered Saccharomyces cerevisiae strains, in which wild type actin was replaced by actin variants with substitutions in residues located on the Ia-actin interface. Expression of the actin mutant Arg177Lys resulted in complete resistance towards Ia. Actin mutation of Asp179 did not change Ia-induced ADP-ribosylation and growth inhibition of S. cerevisiae. By contrast, substitution of Glu270 of actin inhibited the toxic action of Ia and the ADP-ribosylation of actin. In vitro transcribed/translated human β-actin confirmed the crucial role of Glu270 in ADP-ribosylation of actin by Ia.
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Affiliation(s)
- Alexander Belyy
- Gamaleya Research Institute, Moscow, Russia
- Faculty of Biology, Lomonosov Moscow State University, Moscow, Russia
| | | | - Alexander E. Lang
- Institute for Experimental and Clinical Pharmacology and Toxicology, University of Freiburg, Freiburg, Germany
| | - Thomas Jank
- Institute for Experimental and Clinical Pharmacology and Toxicology, University of Freiburg, Freiburg, Germany
| | - Yury Belyi
- Gamaleya Research Institute, Moscow, Russia
- Freiburg Institute for Advanced Studies (FRIAS), University of Freiburg, Freiburg, Germany
| | - Klaus Aktories
- Institute for Experimental and Clinical Pharmacology and Toxicology, University of Freiburg, Freiburg, Germany
- Freiburg Institute for Advanced Studies (FRIAS), University of Freiburg, Freiburg, Germany
- Centre for Biological Signalling Studies (BIOSS), University of Freiburg, Freiburg, Germany
- * E-mail:
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Heisler DB, Kudryashova E, Grinevich DO, Suarez C, Winkelman JD, Birukov KG, Kotha SR, Parinandi NL, Vavylonis D, Kovar DR, Kudryashov DS. ACTIN-DIRECTED TOXIN. ACD toxin-produced actin oligomers poison formin-controlled actin polymerization. Science 2015; 349:535-9. [PMID: 26228148 DOI: 10.1126/science.aab4090] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The actin cross-linking domain (ACD) is an actin-specific toxin produced by several pathogens, including life-threatening spp. of Vibrio cholerae, Vibrio vulnificus, and Aeromonas hydrophila. Actin cross-linking by ACD is thought to lead to slow cytoskeleton failure owing to a gradual sequestration of actin in the form of nonfunctional oligomers. Here, we found that ACD converted cytoplasmic actin into highly toxic oligomers that potently "poisoned" the ability of major actin assembly proteins, formins, to sustain actin polymerization. Thus, ACD can target the most abundant cellular protein by using actin oligomers as secondary toxins to efficiently subvert cellular functions of actin while functioning at very low doses.
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Affiliation(s)
- David B Heisler
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA. The Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA
| | - Elena Kudryashova
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA.
| | - Dmitry O Grinevich
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA
| | - Cristian Suarez
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Jonathan D Winkelman
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Konstantin G Birukov
- Section of Pulmonary and Critical Care and Lung Injury Center, Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
| | - Sainath R Kotha
- Lipid Signaling and Lipidomics Laboratory, Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, Department of Medicine, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University, Columbus, OH 43210, USA
| | - Narasimham L Parinandi
- Lipid Signaling and Lipidomics Laboratory, Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, Department of Medicine, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University, Columbus, OH 43210, USA
| | | | - David R Kovar
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA. Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Dmitri S Kudryashov
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA. The Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA.
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Abstract
Defensins are a class of immune peptides with a broad range of activities against bacterial, fungal and viral pathogens. Besides exerting direct anti-microbial activity via dis-organization of bacterial membranes, defensins are also able to neutralize various unrelated bacterial toxins. Recently, we have demonstrated that in the case of human α- and β-defensins, this later ability is achieved through exploiting toxins' marginal thermodynamic stability, i.e. defensins act as molecular anti-chaperones unfolding toxin molecules and exposing their hydrophobic regions and thus promoting toxin precipitation and inactivation [Kudryashova et al. (2014) Immunity 41, 709-721]. Retrocyclins (RCs) are humanized synthetic θ-defensin peptides that possess unique cyclic structure, differentiating them from α- and β-defensins. Importantly, RCs are more potent against some bacterial and viral pathogens and more stable than their linear counterparts. However, the mechanism of bacterial toxin inactivation by RCs is not known. In the present study, we demonstrate that RCs facilitate unfolding of bacterial toxins. Using differential scanning fluorimetry (DSF), limited proteolysis and collisional quenching of internal tryptophan fluorescence, we show that hydrophobic regions of toxins normally buried in the molecule interior become more exposed to solvents and accessible to proteolytic cleavage in the presence of RCs. The RC-induced unfolding of toxins led to their precipitation and abrogated activity. Toxin inactivation by RCs was strongly diminished under reducing conditions, but preserved at physiological salt and serum concentrations. Therefore, despite significant structural diversity, α-, β- and θ-defensins employ similar mechanisms of toxin inactivation, which may be shared by anti-microbial peptides from other families.
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Dolores JS, Agarwal S, Egerer M, Satchell KJF. Vibrio cholerae MARTX toxin heterologous translocation of beta-lactamase and roles of individual effector domains on cytoskeleton dynamics. Mol Microbiol 2015; 95:590-604. [PMID: 25427654 DOI: 10.1111/mmi.12879] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/18/2014] [Indexed: 12/17/2022]
Abstract
The Vibrio cholerae MARTXVc toxin delivers three effector domains to eukaryotic cells. To study toxin delivery and function of individual domains, the rtxA gene was modified to encode toxin with an in-frame beta-lactamase (Bla) fusion. The hybrid RtxA::Bla toxin was Type I secreted from bacteria; and then Bla was translocated into eukaryotic cells and delivered by autoprocessing, demonstrating that the MARTXVc toxin is capable of heterologous protein transfer. Strains that produce hybrid RtxA::Bla toxins that carry one effector domain in addition to Bla were found to more efficiently translocate Bla. In cell biological assays, the actin cross-linking domain (ACD) and Rho-inactivation domain (RID) are found to cross-link actin and inactivate RhoA, respectively, when other effector domains are absent, with toxin autoprocessing required for high efficiency. The previously unstudied alpha-beta hydrolase domain (ABH) is shown here to activate CDC42, although the effect is ameliorated when RID is also present. Despite all effector domains acting on cytoskeleton assembly, the ACD was sufficient to rapidly inhibit macrophage phagocytosis. Both the ACD and RID independently disrupted polarized epithelial tight junction integrity. The sufficiency of ACD but strong selection for retention of RID and ABH suggests these two domains may primarily function by modulating cell signaling.
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Affiliation(s)
- Jazel S Dolores
- Department of Microbiology-Immunology, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, USA
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13
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Human defensins facilitate local unfolding of thermodynamically unstable regions of bacterial protein toxins. Immunity 2014; 41:709-21. [PMID: 25517613 DOI: 10.1016/j.immuni.2014.10.018] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Accepted: 09/17/2014] [Indexed: 02/08/2023]
Abstract
Defensins are short cationic, amphiphilic, cysteine-rich peptides that constitute the front-line immune defense against various pathogens. In addition to exerting direct antibacterial activities, defensins inactivate several classes of unrelated bacterial exotoxins. To date, no coherent mechanism has been proposed to explain defensins' enigmatic efficiency toward various toxins. In this study, we showed that binding of neutrophil ?-defensin HNP1 to affected bacterial toxins caused their local unfolding, potentiated their thermal melting and precipitation, exposed new regions for proteolysis, and increased susceptibility to collisional quenchers without causing similar effects on tested mammalian structural and enzymatic proteins. Enteric ?-defensin HD5 and ?-defensin hBD2 shared similar toxin-unfolding effects with HNP1, albeit to different degrees. We propose that protein susceptibility to inactivation by defensins is contingent to their thermolability and conformational plasticity and that defensin-induced unfolding is a key element in the general mechanism of toxin inactivation by human defensins.
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Kudryashova E, Heisler D, Zywiec A, Kudryashov DS. Thermodynamic properties of the effector domains of MARTX toxins suggest their unfolding for translocation across the host membrane. Mol Microbiol 2014; 92:1056-71. [PMID: 24724536 DOI: 10.1111/mmi.12615] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/09/2014] [Indexed: 11/28/2022]
Abstract
MARTX (multifunctional autoprocessing repeats-in-toxin) family toxins are produced by Vibrio cholerae, Vibrio vulnificus, Aeromonas hydrophila and other Gram-negative bacteria. Effector domains of MARTX toxins cross the cytoplasmic membrane of a host cell through a putative pore formed by the toxin's glycine-rich repeats. The structure of the pore is unknown and the translocation mechanism of the effector domains is poorly understood. We examined the thermodynamic stability of the effector domains of V. cholerae and A. hydrophila MARTX toxins to elucidate the mechanism of their translocation. We found that all but one domain in each toxin are thermodynamically unstable and several acquire a molten globule state near human physiological temperatures. Fusion of the most stable cysteine protease domain to the adjacent effector domain reduces its thermodynamic stability ∼ 1.4-fold (from D G H 2 O 21.8 to 16.1 kJ mol(-1) ). Precipitation of several individual domains due to thermal denaturation is reduced upon their fusion into multi-domain constructs. We speculate that low thermostability of the MARTX effector domains correlates with that of many other membrane-penetrating toxins and implies their unfolding for cell entry. This study extends the list of thermolabile bacterial toxins, suggesting that this quality is essential and could be susceptible for selective targeting of pathogenic toxins.
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Affiliation(s)
- Elena Kudryashova
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, USA
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