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Tyler JJ, Smaczynska-de Rooij II, Abugharsa L, Palmer JS, Hancock LP, Allwood EG, Ayscough KR. Phosphorylation of the WH2 domain in yeast Las17/WASP regulates G-actin binding and protein function during endocytosis. Sci Rep 2021; 11:9718. [PMID: 33958621 PMCID: PMC8102491 DOI: 10.1038/s41598-021-88826-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Accepted: 04/12/2021] [Indexed: 11/29/2022] Open
Abstract
Actin nucleation is the key rate limiting step in the process of actin polymerization, and tight regulation of this process is critical to ensure actin filaments form only at specific times and at defined regions of the cell. WH2 domains are short sequence motifs found in many different actin binding proteins including WASP family proteins which regulate the actin nucleating complex Arp2/3. In this study we reveal a phosphorylation site, Serine 554, within the WH2 domain of the yeast WASP homologue Las17. Both phosphorylation and a phospho-mimetic mutation reduce actin monomer binding affinity while an alanine mutation, generated to mimic the non-phosphorylated state, increases actin binding affinity. The effect of these mutations on the Las17-dependent process of endocytosis in vivo was analysed and leads us to propose that switching of Las17 phosphorylation states may allow progression through distinct phases of endocytosis from site assembly through to the final scission stage. While the study is focused on Las17, the sole WASP family protein in yeast, our results have broad implications for our understanding of how a key residue in this conserved motif can underpin the many different actin regulatory roles with which WH2 domains have been associated.
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Affiliation(s)
- J J Tyler
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, S10 2TN, UK
| | - I I Smaczynska-de Rooij
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, S10 2TN, UK
| | - L Abugharsa
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, S10 2TN, UK
| | - J S Palmer
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, S10 2TN, UK
| | - L P Hancock
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, S10 2TN, UK
| | - E G Allwood
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, S10 2TN, UK
| | - K R Ayscough
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, S10 2TN, UK.
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2
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Bradley AO, Vizcarra CL, Bailey HM, Quinlan ME. Spire stimulates nucleation by Cappuccino and binds both ends of actin filaments. Mol Biol Cell 2019; 31:273-286. [PMID: 31877067 PMCID: PMC7183766 DOI: 10.1091/mbc.e19-09-0550] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The actin nucleators Spire and Cappuccino synergize to promote actin assembly, but the mechanism of their synergy is controversial. Together these proteins promote the formation of actin meshes, which are conserved structures that regulate the establishment of oocyte polarity. Direct interaction between Spire and Cappuccino is required for oogenesis and for in vitro synergistic actin assembly. This synergy is proposed to be driven by elongation and the formation of a ternary complex at filament barbed ends, or by nucleation and interaction at filament pointed ends. To mimic the geometry of Spire and Cappuccino in vivo, we immobilized Spire on beads and added Cappuccino and actin. Barbed ends, protected by Cappuccino, grow away from the beads while pointed ends are retained, as expected for nucleation-driven synergy. We found that Spire is sufficient to bind barbed ends and retain pointed ends of actin filaments near beads and we identified Spire’s barbed-end binding domain. Loss of barbed-end binding increases nucleation by Spire and synergy with Cappuccino in bulk pyrene assays and on beads. Importantly, genetic rescue by the loss-of-function mutant indicates that barbed-end binding is not necessary for oogenesis. Thus, increased nucleation is a critical element of synergy both in vitro and in vivo.
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Affiliation(s)
- Alexander O Bradley
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095
| | - Christina L Vizcarra
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095
| | - Hannah M Bailey
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095
| | - Margot E Quinlan
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095.,Molecular Biology Institute, University of California, Los Angeles, Los Angeles, CA 90095
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3
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Vorontsova JE, Zavoloka EL, Cherezov RO, Simonova OB. Three Important Discoveries in the Field of the Cytoskeleton’s Proteins Functioning on the Drosophila melanogaster Model. Mol Biol 2019. [DOI: 10.1134/s0026893319010163] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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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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Functional Actin Networks under Construction: The Cooperative Action of Actin Nucleation and Elongation Factors. Trends Biochem Sci 2017; 42:414-430. [DOI: 10.1016/j.tibs.2017.03.002] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Revised: 03/04/2017] [Accepted: 03/07/2017] [Indexed: 12/31/2022]
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6
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Burke TA, Harker AJ, Dominguez R, Kovar DR. The bacterial virulence factors VopL and VopF nucleate actin from the pointed end. J Cell Biol 2017; 216:1267-1276. [PMID: 28363971 PMCID: PMC5412564 DOI: 10.1083/jcb.201608104] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Revised: 01/31/2017] [Accepted: 02/16/2017] [Indexed: 11/22/2022] Open
Abstract
How the bacterial virulence factors VopL/F from Vibrio catalyze actin nucleation is unclear. Using multicolor TIRF microscopy imaging, Burke et al. find that VopL and VopF stimulate actin assembly via identical pointed-end nucleation mechanisms. VopL and VopF (VopL/F) are tandem WH2-domain actin assembly factors used by infectious Vibrio species to induce actin assembly in host cells. There is disagreement about the filament assembly mechanism of VopL/F, including whether they associate with the filament barbed or pointed end. Here, we used multicolor total internal reflection fluorescence microscopy to directly observe actin assembly with fluorescently labeled VopL/F. In actin monomer assembly reactions, VopL/F exclusively nucleate actin filament assemblies, remaining only briefly associated with the pointed end. VopL/F do not associate with the ends of preassembled filaments. In assembly reactions with saturating profilin, ∼85% of VopL/F molecules also promote nucleation from the pointed end, whereas a smaller fraction (<15%) associate for ∼25 s with the barbed end of preassembled filaments, inhibiting their elongation. We conclude that VopL/F function primarily as actin nucleation factors that remain briefly (∼100 s) associated with the pointed end.
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Affiliation(s)
- Thomas A Burke
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637
| | - Alyssa J Harker
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637
| | - Roberto Dominguez
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | - David R Kovar
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637 .,Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637
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Rodal AA, Del Signore SJ, Martin AC. Drosophila comes of age as a model system for understanding the function of cytoskeletal proteins in cells, tissues, and organisms. Cytoskeleton (Hoboken) 2015; 72:207-24. [PMID: 26074334 DOI: 10.1002/cm.21228] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2015] [Revised: 06/11/2015] [Accepted: 06/11/2015] [Indexed: 01/30/2023]
Abstract
For the last 100 years, Drosophila melanogaster has been a powerhouse genetic system for understanding mechanisms of inheritance, development, and behavior in animals. In recent years, advances in imaging and genetic tools have led to Drosophila becoming one of the most effective systems for unlocking the subcellular functions of proteins (and particularly cytoskeletal proteins) in complex developmental settings. In this review, written for non-Drosophila experts, we will discuss critical technical advances that have enabled these cell biological insights, highlighting three examples of cytoskeletal discoveries that have arisen as a result: (1) regulation of Arp2/3 complex in myoblast fusion, (2) cooperation of the actin filament nucleators Spire and Cappuccino in establishment of oocyte polarity, and (3) coordination of supracellular myosin cables. These specific examples illustrate the unique power of Drosophila both to uncover new cytoskeletal structures and functions, and to place these discoveries in a broader in vivo context, providing insights that would have been impossible in a cell culture model or in vitro. Many of the cellular structures identified in Drosophila have clear counterparts in mammalian cells and tissues, and therefore elucidating cytoskeletal functions in Drosophila will be broadly applicable to other organisms.
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Affiliation(s)
- Avital A Rodal
- Department of Biology, Brandeis University, Waltham, Massachusetts
| | | | - Adam C Martin
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts
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Park E, Graziano BR, Zheng W, Garabedian M, Goode BL, Eck MJ. Structure of a Bud6/Actin Complex Reveals a Novel WH2-like Actin Monomer Recruitment Motif. Structure 2015; 23:1492-1499. [PMID: 26118535 DOI: 10.1016/j.str.2015.05.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Revised: 04/22/2015] [Accepted: 05/11/2015] [Indexed: 10/23/2022]
Abstract
In budding yeast, the actin-binding protein Bud6 cooperates with formins Bni1 and Bnr1 to catalyze the assembly of actin filaments. The nucleation-enhancing activity of Bud6 requires both a "core" domain that binds to the formin and a "flank" domain that binds monomeric actin. Here, we describe the structure of the Bud6 flank domain in complex with actin. Two helices in Bud6(flank) interact with actin; one binds in a groove at the barbed end of the actin monomer in a manner closely resembling the helix of WH2 domains, a motif found in many actin nucleation factors. The second helix rises along the face of actin. Mutational analysis verifies the importance of these Bud6-actin contacts for nucleation-enhancing activity. The Bud6 binding site on actin overlaps with that of the formin FH2 domain and is also incompatible with inter-subunit contacts in F-actin, suggesting that Bud6 interacts only transiently with actin monomers during filament nucleation.
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Affiliation(s)
- Eunyoung Park
- Department of Cancer Biology, Dana-Farber Cancer Institute, SM1036, 450 Brookline Avenue, Boston, MA 02215, USA; Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02215, USA
| | - Brian R Graziano
- Department of Biology, Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, MA 02454, USA
| | - Wei Zheng
- Department of Cancer Biology, Dana-Farber Cancer Institute, SM1036, 450 Brookline Avenue, Boston, MA 02215, USA; Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02215, USA
| | - Mikael Garabedian
- Department of Biology, Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, MA 02454, USA
| | - Bruce L Goode
- Department of Biology, Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, MA 02454, USA
| | - Michael J Eck
- Department of Cancer Biology, Dana-Farber Cancer Institute, SM1036, 450 Brookline Avenue, Boston, MA 02215, USA; Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02215, USA.
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Cenik BK, Garg A, McAnally JR, Shelton JM, Richardson JA, Bassel-Duby R, Olson EN, Liu N. Severe myopathy in mice lacking the MEF2/SRF-dependent gene leiomodin-3. J Clin Invest 2015; 125:1569-78. [PMID: 25774500 DOI: 10.1172/jci80115] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2014] [Accepted: 01/29/2015] [Indexed: 01/18/2023] Open
Abstract
Maintenance of skeletal muscle structure and function requires a precise stoichiometry of sarcomeric proteins for proper assembly of the contractile apparatus. Absence of components of the sarcomeric thin filaments causes nemaline myopathy, a lethal congenital muscle disorder associated with aberrant myofiber structure and contractility. Previously, we reported that deficiency of the kelch-like family member 40 (KLHL40) in mice results in nemaline myopathy and destabilization of leiomodin-3 (LMOD3). LMOD3 belongs to a family of tropomodulin-related proteins that promote actin nucleation. Here, we show that deficiency of LMOD3 in mice causes nemaline myopathy. In skeletal muscle, transcription of Lmod3 was controlled by the transcription factors SRF and MEF2. Myocardin-related transcription factors (MRTFs), which function as SRF coactivators, serve as sensors of actin polymerization and are sequestered in the cytoplasm by actin monomers. Conversely, conditions that favor actin polymerization de-repress MRTFs and activate SRF-dependent genes. We demonstrated that the actin nucleator LMOD3, together with its stabilizing partner KLHL40, enhances MRTF-SRF activity. In turn, SRF cooperated with MEF2 to sustain the expression of LMOD3 and other components of the contractile apparatus, thereby establishing a regulatory circuit to maintain skeletal muscle function. These findings provide insight into the molecular basis of the sarcomere assembly and muscle dysfunction associated with nemaline myopathy.
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