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Kadzik RS, Kovar DR. A step-by-step guide to fragmenting bundled actin filaments. J Cell Biol 2024; 223:e202403191. [PMID: 38748453 PMCID: PMC11096848 DOI: 10.1083/jcb.202403191] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/18/2024] Open
Abstract
There has long been conflicting evidence as to how bundled actin filaments, found in cellular structures such as filopodia, are disassembled. In this issue, Chikireddy et al. (https://doi.org/10.1083/jcb.202312106) provide a detailed in vitro analysis of the steps involved in fragmentation of fascin-bundled actin filaments and propose a novel mechanism for severing two-filament bundles.
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Affiliation(s)
- Rachel S. Kadzik
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL, USA
| | - David R. Kovar
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL, USA
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
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2
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Chikireddy J, Lengagne L, Le Borgne R, Durieu C, Wioland H, Romet-Lemonne G, Jégou A. Fascin-induced bundling protects actin filaments from disassembly by cofilin. J Cell Biol 2024; 223:e202312106. [PMID: 38497788 PMCID: PMC10949937 DOI: 10.1083/jcb.202312106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Revised: 02/26/2024] [Accepted: 02/29/2024] [Indexed: 03/19/2024] Open
Abstract
Actin filament turnover plays a central role in shaping actin networks, yet the feedback mechanism between network architecture and filament assembly dynamics remains unclear. The activity of ADF/cofilin, the main protein family responsible for filament disassembly, has been mainly studied at the single filament level. This study unveils that fascin, by crosslinking filaments into bundles, strongly slows down filament disassembly by cofilin. We show that this is due to a markedly slower initiation of the first cofilin clusters, which occurs up to 100-fold slower on large bundles compared with single filaments. In contrast, severing at cofilin cluster boundaries is unaffected by fascin bundling. After the formation of an initial cofilin cluster on a filament within a bundle, we observed the local removal of fascin. Notably, the formation of cofilin clusters on adjacent filaments is highly enhanced, locally. We propose that this interfilament cooperativity arises from the local propagation of the cofilin-induced change in helicity from one filament to the other filaments of the bundle. Overall, taking into account all the above reactions, we reveal that fascin crosslinking slows down the disassembly of actin filaments by cofilin. These findings highlight the important role played by crosslinkers in tuning actin network turnover by modulating the activity of other regulatory proteins.
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Affiliation(s)
| | - Léana Lengagne
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
| | - Rémi Le Borgne
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
| | - Catherine Durieu
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
| | - Hugo Wioland
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
| | | | - Antoine Jégou
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
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3
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Homa KE, Hocky GM, Suarez C, Kovar DR. Arp2/3 complex- and formin-mediated actin cytoskeleton networks facilitate actin binding protein sorting in fission yeast. Eur J Cell Biol 2024; 103:151404. [PMID: 38493594 PMCID: PMC11211059 DOI: 10.1016/j.ejcb.2024.151404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2023] [Revised: 03/01/2024] [Accepted: 03/13/2024] [Indexed: 03/19/2024] Open
Abstract
While it is well-established that F-actin networks with specific organizations and dynamics are tightly regulated by distinct sets of associated actin-binding proteins (ABPs), how ABPs self-sort to particular F-actin networks remains largely unclear. We report that actin assembly factors Arp2/3 complex and formin Cdc12 tune the association of ABPs fimbrin Fim1 and tropomyosin Cdc8 to different F-actin networks in fission yeast. Genetic and pharmacological disruption of F-actin networks revealed that Fim1 is preferentially directed to Arp2/3-complex mediated actin patches, whereas Cdc8 is preferentially targeted to formin Cdc12-mediated filaments in the contractile ring. To investigate the role of Arp2/3 complex- and formin Cdc12-mediated actin assembly, we used four-color TIRF microscopy to observe the in vitro reconstitution of ABP sorting with purified proteins. Fim1 or Cdc8 alone bind similarly well to filaments assembled by either assembly factor. However, in 'competition' reactions containing both actin assembly factors and both ABPs, ∼2.0-fold more Fim1 and ∼3.5-fold more Cdc8 accumulates on Arp2/3 complex branch points and formin Cdc12-assembled actin filaments, respectively. These findings indicate that F-actin assembly factors Arp2/3 complex and formin Cdc12 help facilitate the recruitment of specific ABPs, thereby tuning ABP sorting and subsequently establishing the identity of F-actin networks in fission yeast.
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Affiliation(s)
- Kaitlin E Homa
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL, United States
| | - Glen M Hocky
- Department of Chemistry, New York University, New York, NY, United States
| | - Cristian Suarez
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL, United States
| | - David R Kovar
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL, United States; Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, United States.
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4
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Morales EA, Fitz GN, Tyska MJ. Mitotic spindle positioning protein (MISP) preferentially binds to aged F-actin. J Biol Chem 2024; 300:107279. [PMID: 38588808 PMCID: PMC11101845 DOI: 10.1016/j.jbc.2024.107279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2023] [Revised: 03/14/2024] [Accepted: 04/01/2024] [Indexed: 04/10/2024] Open
Abstract
Actin bundling proteins crosslink filaments into polarized structures that shape and support membrane protrusions including filopodia, microvilli, and stereocilia. In the case of epithelial microvilli, mitotic spindle positioning protein (MISP) is an actin bundler that localizes specifically to the basal rootlets, where the pointed ends of core bundle filaments converge. Previous studies established that MISP is prevented from binding more distal segments of the core bundle by competition with other actin-binding proteins. Yet whether MISP holds a preference for binding directly to rootlet actin remains an open question. By immunostaining native intestinal tissue sections, we found that microvillar rootlets are decorated with the severing protein, cofilin, suggesting high levels of ADP-actin in these structures. Using total internal reflection fluorescence microscopy assays, we also found that purified MISP exhibits a binding preference for ADP- versus ADP-Pi-actin-containing filaments. Consistent with this, assays with actively growing actin filaments revealed that MISP binds at or near their pointed ends. Moreover, although substrate attached MISP assembles filament bundles in parallel and antiparallel configurations, in solution MISP assembles parallel bundles consisting of multiple filaments exhibiting uniform polarity. These discoveries highlight nucleotide state sensing as a mechanism for sorting actin bundlers along filaments and driving their accumulation near filament ends. Such localized binding might drive parallel bundle formation and/or locally modulate bundle mechanical properties in microvilli and related protrusions.
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Affiliation(s)
- E Angelo Morales
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, Tennessee, USA
| | - Gillian N Fitz
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, Tennessee, USA
| | - Matthew J Tyska
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, Tennessee, USA.
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5
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Shehjar F, Almarghalani DA, Mahajan R, Hasan SAM, Shah ZA. The Multifaceted Role of Cofilin in Neurodegeneration and Stroke: Insights into Pathogenesis and Targeting as a Therapy. Cells 2024; 13:188. [PMID: 38247879 PMCID: PMC10814918 DOI: 10.3390/cells13020188] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Revised: 01/03/2024] [Accepted: 01/10/2024] [Indexed: 01/23/2024] Open
Abstract
This comprehensive review explores the complex role of cofilin, an actin-binding protein, across various neurodegenerative diseases (Alzheimer's, Parkinson's, schizophrenia, amyotrophic lateral sclerosis (ALS), Huntington's) and stroke. Cofilin is an essential protein in cytoskeletal dynamics, and any dysregulation could lead to potentially serious complications. Cofilin's involvement is underscored by its impact on pathological hallmarks like Aβ plaques and α-synuclein aggregates, triggering synaptic dysfunction, dendritic spine loss, and impaired neuronal plasticity, leading to cognitive decline. In Parkinson's disease, cofilin collaborates with α-synuclein, exacerbating neurotoxicity and impairing mitochondrial and axonal function. ALS and frontotemporal dementia showcase cofilin's association with genetic factors like C9ORF72, affecting actin dynamics and contributing to neurotoxicity. Huntington's disease brings cofilin into focus by impairing microglial migration and influencing synaptic plasticity through AMPA receptor regulation. Alzheimer's, Parkinson's, and schizophrenia exhibit 14-3-3 proteins in cofilin dysregulation as a shared pathological mechanism. In the case of stroke, cofilin takes center stage, mediating neurotoxicity and neuronal cell death. Notably, there is a potential overlap in the pathologies and involvement of cofilin in various diseases. In this context, referencing cofilin dysfunction could provide valuable insights into the common pathologies associated with the aforementioned conditions. Moreover, this review explores promising therapeutic interventions, including cofilin inhibitors and gene therapy, demonstrating efficacy in preclinical models. Challenges in inhibitor development, brain delivery, tissue/cell specificity, and long-term safety are acknowledged, emphasizing the need for precision drug therapy. The call to action involves collaborative research, biomarker identification, and advancing translational efforts. Cofilin emerges as a pivotal player, offering potential as a therapeutic target. However, unraveling its complexities requires concerted multidisciplinary efforts for nuanced and effective interventions across the intricate landscape of neurodegenerative diseases and stroke, presenting a hopeful avenue for improved patient care.
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Affiliation(s)
- Faheem Shehjar
- Department of Medicinal and Biological Chemistry, College of Pharmacy and Pharmaceutical Sciences, Toledo, OH 43614, USA; (F.S.); (R.M.)
| | - Daniyah A. Almarghalani
- Stroke Research Unit, Department of Pharmacology and Toxicology, College of Pharmacy, Taif University, P.O. Box 11099, Taif 21944, Saudi Arabia;
| | - Reetika Mahajan
- Department of Medicinal and Biological Chemistry, College of Pharmacy and Pharmaceutical Sciences, Toledo, OH 43614, USA; (F.S.); (R.M.)
| | - Syed A.-M. Hasan
- Department of Pharmacology and Experimental Therapeutics, College of Pharmacy and Pharmaceutical Sciences, University of Toledo, Toledo, OH 43614, USA;
| | - Zahoor A. Shah
- Department of Medicinal and Biological Chemistry, College of Pharmacy and Pharmaceutical Sciences, Toledo, OH 43614, USA; (F.S.); (R.M.)
- Department of Pharmacology and Experimental Therapeutics, College of Pharmacy and Pharmaceutical Sciences, University of Toledo, Toledo, OH 43614, USA;
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6
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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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7
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Gonzalez Rodriguez S, Wirshing AC, Goodman AL, Goode BL. Cytosolic concentrations of actin binding proteins and the implications for in vivo F-actin turnover. J Cell Biol 2023; 222:e202306036. [PMID: 37801069 PMCID: PMC10558290 DOI: 10.1083/jcb.202306036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2023] [Revised: 08/31/2023] [Accepted: 09/21/2023] [Indexed: 10/07/2023] Open
Abstract
Understanding how numerous actin-binding proteins (ABPs) work in concert to control the assembly, organization, and turnover of the actin cytoskeleton requires quantitative information about the levels of each component. Here, we measured the cellular concentrations of actin and the majority of the conserved ABPs in Saccharomyces cerevisiae, as well as the free (cytosolic) fractions of each ABP. The cellular concentration of actin is estimated to be 13.2 µM, with approximately two-thirds in the F-actin form and one-third in the G-actin form. Cellular concentrations of ABPs range from 12.4 to 0.85 µM (Tpm1> Pfy1> Cof1> Abp1> Srv2> Abp140> Tpm2> Aip1> Cap1/2> Crn1> Sac6> Twf1> Arp2/3> Scp1). The cytosolic fractions of all ABPs are unexpectedly high (0.6-0.9) and remain so throughout the cell cycle. Based on these numbers, we speculate that F-actin binding sites are limited in vivo, which leads to high cytosolic levels of ABPs, and in turn helps drive the rapid assembly and turnover of cellular F-actin structures.
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Affiliation(s)
- Sofia Gonzalez Rodriguez
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA, USA
| | - Alison C.E. Wirshing
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA, USA
| | - Anya L. Goodman
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA, USA
- Department of Chemistry and Biochemistry, California Polytechnic State University SLO, San Luis Obispo, CA, USA
| | - Bruce L. Goode
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA, USA
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8
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Alimov N, Hoeprich GJ, Padrick SB, Goode BL. Cyclase-associated protein interacts with actin filament barbed ends to promote depolymerization and formin displacement. J Biol Chem 2023; 299:105367. [PMID: 37863260 PMCID: PMC10692737 DOI: 10.1016/j.jbc.2023.105367] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2023] [Revised: 10/04/2023] [Accepted: 10/12/2023] [Indexed: 10/22/2023] Open
Abstract
Cyclase-associated protein (CAP) has emerged as a central player in cellular actin turnover, but its molecular mechanisms of action are not yet fully understood. Recent studies revealed that the N terminus of CAP interacts with the pointed ends of actin filaments to accelerate depolymerization in conjunction with cofilin. Here, we use in vitro microfluidics-assisted TIRF microscopy to show that the C terminus of CAP promotes depolymerization at the opposite (barbed) ends of actin filaments. In the absence of actin monomers, full-length mouse CAP1 and C-terminal halves of CAP1 (C-CAP1) and CAP2 (C-CAP2) accelerate barbed end depolymerization. Using mutagenesis and structural modeling, we show that these activities are mediated by the WH2 and CARP domains of CAP. In addition, we observe that CAP collaborates with profilin to accelerate barbed end depolymerization and that these effects depend on their direct interaction, providing the first known example of CAP-profilin collaborative effects in regulating actin. In the presence of actin monomers, CAP1 attenuates barbed end growth and promotes formin dissociation. Overall, these findings demonstrate that CAP uses distinct domains and mechanisms to interact with opposite ends of actin filaments and drive turnover. Further, they contribute to the emerging view of actin barbed ends as sites of dynamic molecular regulation, where numerous proteins compete and cooperate with each other to tune polymer dynamics, similar to the rich complexity seen at microtubule ends.
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Affiliation(s)
- Nikita Alimov
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, Massachusetts, USA
| | - Gregory J Hoeprich
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, Massachusetts, USA
| | - Shae B Padrick
- Department of Biochemistry and Molecular Biology, Drexel University, Philadelphia, Pennsylvania, USA
| | - Bruce L Goode
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, Massachusetts, USA.
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9
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Cao W, Taylor EW, De La Cruz EM. Cooperative ligand binding to a double-stranded Ising lattice-Application to cofilin binding to actin filaments. PNAS NEXUS 2023; 2:pgad331. [PMID: 37885622 PMCID: PMC10599439 DOI: 10.1093/pnasnexus/pgad331] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/24/2023] [Accepted: 10/02/2023] [Indexed: 10/28/2023]
Abstract
Cooperative ligand binding to linear polymers is fundamental in many scientific disciplines, particularly biological and chemical physics and engineering. Such ligand binding interactions have been widely modeled using infinite one-dimensional (1D) Ising models even in cases where the linear polymers are more complex (e.g. actin filaments and other double-stranded linear polymers). Here, we use sequence-generating and transfer matrix methods to obtain an analytical method for cooperative equilibrium ligand binding to double-stranded Ising lattices. We use this exact solution to evaluate binding properties and features and analyze experimental binding data of cooperative binding of the regulatory protein, cofilin, to actin filaments. This analysis, with additional experimental information about the observed bound cofilin cluster sizes and filament structure, reveals that a bound cofilin promotes cooperative binding to its longitudinal nearest-neighbors but has very modest effects on lateral nearest-neighbors. The bound cofilin cluster sizes calculated from the best fit parameters from the double-stranded model are considerably larger than when calculated with the 1D model, consistent with experimental observations made by electron microscopy and fluorescence imaging. The exact solution obtained and the method for using the solution developed here can be widely used for analysis of variety of multistranded lattice systems.
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Affiliation(s)
- Wenxiang Cao
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Edwin W Taylor
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Enrique M De La Cruz
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
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10
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Morales EA, Tyska MJ. Mitotic spindle positioning protein (MISP) is an actin bundler that senses ADP-actin and binds near the pointed ends of filaments. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.05.539649. [PMID: 37205433 PMCID: PMC10187293 DOI: 10.1101/2023.05.05.539649] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Actin bundling proteins crosslink filaments into polarized structures that shape and support membrane protrusions including filopodia, microvilli, and stereocilia. In the case of epithelial microvilli, mitotic spindle positioning protein (MISP) is an actin bundler that localizes specifically to the basal rootlets, where the pointed ends of core bundle filaments converge. Previous studies established that MISP is prevented from binding more distal segments of the core bundle by competition with other actin binding proteins. Yet whether MISP holds a preference for binding directly to rootlet actin remains an open question. Using in vitro TIRF microscopy assays, we found that MISP exhibits a clear binding preference for filaments enriched in ADP-actin monomers. Consistent with this, assays with actively growing actin filaments revealed that MISP binds at or near their pointed ends. Moreover, although substrate attached MISP assembles filament bundles in parallel and antiparallel configurations, in solution MISP assembles parallel bundles consisting of multiple filaments exhibiting uniform polarity. These discoveries highlight nucleotide state sensing as a mechanism for sorting actin bundlers along filaments and driving their accumulation near filament ends. Such localized binding might drive parallel bundle formation and/or locally modulate bundle mechanical properties in microvilli and related protrusions.
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11
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Tang Q, Pollard LW, Homa KE, Kovar DR, Trybus KM. Acetylation of fission yeast tropomyosin does not promote differential association with cognate formins. Cytoskeleton (Hoboken) 2023; 80:77-92. [PMID: 36692369 PMCID: PMC10121778 DOI: 10.1002/cm.21745] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Revised: 01/02/2023] [Accepted: 01/17/2023] [Indexed: 01/25/2023]
Abstract
It was proposed from cellular studies that S. pombe tropomyosin Cdc8 (Tpm) segregates into two populations due to the presence or absence of an amino-terminal acetylation that specifies which formin-mediated F-actin networks it binds, but with no supporting biochemistry. To address this mechanism in vitro, we developed methods for S. pombe actin expression in Sf9 cells. We then employed 3-color TIRF microscopy using all recombinant S. pombe proteins to probe in vitro multicomponent mechanisms involving actin, acetylated and unacetylated Tpm, formins, and myosins. Acetyl-Tpm exhibits tight binding to actin in contrast to weaker binding by unacetylated Tpm. In disagreement with the differential recruitment model, Tpm showed no preferential binding to filaments assembled by the FH1-FH2-domains of two S. pombe formins, nor did Tpm binding have any bias towards the growing formin-bound actin filament barbed end. Although our in vitro findings do not support a direct formin-tropomyosin interaction, it is possible that formins bias differential tropomyosin isoform recruitment through undiscovered mechanisms. Importantly, despite a 12% sequence divergence between skeletal and S. pombe actin, S. pombe myosins Myo2 and Myo51 exhibited similar motile behavior with these two actins, validating key prior findings with these myosins that used skeletal actin.
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Affiliation(s)
- Qing Tang
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington VT
| | - Luther W. Pollard
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington VT
| | - Kaitlin E. Homa
- Molecular Genetics and Cell Biology, Biochemistry and Molecular Biology, the University of Chicago, Chicago, IL
| | - David R. Kovar
- Molecular Genetics and Cell Biology, Biochemistry and Molecular Biology, the University of Chicago, Chicago, IL
| | - Kathleen M. Trybus
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington VT
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12
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Rajan S, Kudryashov DS, Reisler E. Actin Bundles Dynamics and Architecture. Biomolecules 2023; 13:450. [PMID: 36979385 PMCID: PMC10046292 DOI: 10.3390/biom13030450] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2022] [Revised: 02/16/2023] [Accepted: 02/20/2023] [Indexed: 03/04/2023] Open
Abstract
Cells use the actin cytoskeleton for many of their functions, including their division, adhesion, mechanosensing, endo- and phagocytosis, migration, and invasion. Actin bundles are the main constituent of actin-rich structures involved in these processes. An ever-increasing number of proteins that crosslink actin into bundles or regulate their morphology is being identified in cells. With recent advances in high-resolution microscopy and imaging techniques, the complex process of bundles formation and the multiple forms of physiological bundles are beginning to be better understood. Here, we review the physiochemical and biological properties of four families of highly conserved and abundant actin-bundling proteins, namely, α-actinin, fimbrin/plastin, fascin, and espin. We describe the similarities and differences between these proteins, their role in the formation of physiological actin bundles, and their properties-both related and unrelated to their bundling abilities. We also review some aspects of the general mechanism of actin bundles formation, which are known from the available information on the activity of the key actin partners involved in this process.
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Affiliation(s)
- Sudeepa Rajan
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA
| | - Dmitri S. Kudryashov
- Department of Chemistry and Biochemistry, Ohio State University, Columbus, OH 43210, USA
| | - Emil Reisler
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA
- Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA
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13
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Selvaraj M, Kokate SB, Reggiano G, Kogan K, Kotila T, Kremneva E, DiMaio F, Lappalainen P, Huiskonen JT. Structural basis underlying specific biochemical activities of non-muscle tropomyosin isoforms. Cell Rep 2023; 42:111900. [PMID: 36586407 DOI: 10.1016/j.celrep.2022.111900] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Revised: 11/03/2022] [Accepted: 12/07/2022] [Indexed: 12/31/2022] Open
Abstract
The actin cytoskeleton is critical for cell migration, morphogenesis, endocytosis, organelle dynamics, and cytokinesis. To support diverse cellular processes, actin filaments form a variety of structures with specific architectures and dynamic properties. Key proteins specifying actin filaments are tropomyosins. Non-muscle cells express several functionally non-redundant tropomyosin isoforms, which differentially control the interactions of other proteins, including myosins and ADF/cofilin, with actin filaments. However, the underlying molecular mechanisms have remained elusive. By determining the cryogenic electron microscopy structures of actin filaments decorated by two functionally distinct non-muscle tropomyosin isoforms, Tpm1.6 and Tpm3.2, we reveal that actin filament conformation remains unaffected upon binding. However, Tpm1.6 and Tpm3.2 follow different paths along the actin filament major groove, providing an explanation for their incapability to co-polymerize on actin filaments. We also elucidate the molecular basis underlying specific roles of Tpm1.6 and Tpm3.2 in myosin II activation and protecting actin filaments from ADF/cofilin-catalyzed severing.
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Affiliation(s)
- Muniyandi Selvaraj
- Institute of Biotechnology, Helsinki Institute of Life Science HiLIFE, University of Helsinki, P.O. Box 56, 00014 Helsinki, Finland
| | - Shrikant B Kokate
- Institute of Biotechnology, Helsinki Institute of Life Science HiLIFE, University of Helsinki, P.O. Box 56, 00014 Helsinki, Finland
| | - Gabriella Reggiano
- Department of Biochemistry, University of Washington, Seattle, WA 98195, USA
| | - Konstantin Kogan
- Institute of Biotechnology, Helsinki Institute of Life Science HiLIFE, University of Helsinki, P.O. Box 56, 00014 Helsinki, Finland
| | - Tommi Kotila
- Institute of Biotechnology, Helsinki Institute of Life Science HiLIFE, University of Helsinki, P.O. Box 56, 00014 Helsinki, Finland
| | - Elena Kremneva
- Institute of Biotechnology, Helsinki Institute of Life Science HiLIFE, University of Helsinki, P.O. Box 56, 00014 Helsinki, Finland
| | - Frank DiMaio
- Department of Biochemistry, University of Washington, Seattle, WA 98195, USA
| | - Pekka Lappalainen
- Institute of Biotechnology, Helsinki Institute of Life Science HiLIFE, University of Helsinki, P.O. Box 56, 00014 Helsinki, Finland.
| | - Juha T Huiskonen
- Institute of Biotechnology, Helsinki Institute of Life Science HiLIFE, University of Helsinki, P.O. Box 56, 00014 Helsinki, Finland.
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14
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Kudryashova E, Ankita, Ulrichs H, Shekhar S, Kudryashov DS. Pointed-end processive elongation of actin filaments by Vibrio effectors VopF and VopL. SCIENCE ADVANCES 2022; 8:eadc9239. [PMID: 36399577 PMCID: PMC9674292 DOI: 10.1126/sciadv.adc9239] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2022] [Accepted: 10/03/2022] [Indexed: 07/20/2023]
Abstract
According to the cellular actin dynamics paradigm, filaments grow at their barbed ends and depolymerize predominantly from their pointed ends to form polar structures and do productive work. We show that actin can elongate at the pointed end when assisted by Vibrio VopF/L toxins, which act as processive polymerases. In cells, processively moving VopF/L speckles are inhibited by factors blocking the pointed but not barbed ends. Multispectral single-molecule imaging confirmed that VopF molecules associate with the pointed end, actively promoting its elongation even in the presence of profilin. Consequently, VopF/L can break the actin cytoskeleton's polarity by compromising actin-based cellular processes. Therefore, actin filament design allows processive growth at both ends, which suggests unforeseen possibilities for cellular actin organization, particularly in specialized cells and compartments.
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Affiliation(s)
- Elena Kudryashova
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA
| | - Ankita
- Department of Physics, Emory University, Atlanta, GA 30322, USA
- Department of Cell Biology, Emory University, Atlanta, GA 30322, USA
| | - Heidi Ulrichs
- Department of Physics, Emory University, Atlanta, GA 30322, USA
- Department of Cell Biology, Emory University, Atlanta, GA 30322, USA
| | - Shashank Shekhar
- Department of Physics, Emory University, Atlanta, GA 30322, USA
- Department of Cell Biology, Emory University, Atlanta, GA 30322, USA
| | - Dmitri S. Kudryashov
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA
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15
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Hatano T, Lim TC, Billault-Chaumartin I, Dhar A, Gu Y, Massam-Wu T, Scott W, Adishesha S, Chapa-y-Lazo B, Springall L, Sivashanmugam L, Mishima M, Martin SG, Oliferenko S, Palani S, Balasubramanian MK. mNG-tagged fusion proteins and nanobodies to visualize tropomyosins in yeast and mammalian cells. J Cell Sci 2022; 135:jcs260288. [PMID: 36148799 PMCID: PMC9592052 DOI: 10.1242/jcs.260288] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Accepted: 08/15/2022] [Indexed: 11/20/2022] Open
Abstract
Tropomyosins are structurally conserved α-helical coiled-coil proteins that bind along the length of filamentous actin (F-actin) in fungi and animals. Tropomyosins play essential roles in the stability of actin filaments and in regulating myosin II contractility. Despite the crucial role of tropomyosin in actin cytoskeletal regulation, in vivo investigations of tropomyosin are limited, mainly due to the suboptimal live-cell imaging tools currently available. Here, we report on an mNeonGreen (mNG)-tagged tropomyosin, with native promoter and linker length configuration, that clearly reports tropomyosin dynamics in Schizosaccharomyces pombe (Cdc8), Schizosaccharomyces japonicus (Cdc8) and Saccharomyces cerevisiae (Tpm1 and Tpm2). We also describe a fluorescent probe to visualize mammalian tropomyosin (TPM2 isoform). Finally, we generated a camelid nanobody against S. pombe Cdc8, which mimics the localization of mNG-Cdc8 in vivo. Using these tools, we report the presence of tropomyosin in previously unappreciated patch-like structures in fission and budding yeasts, show flow of tropomyosin (F-actin) cables to the cytokinetic actomyosin ring and identify rearrangements of the actin cytoskeleton during mating. These powerful tools and strategies will aid better analyses of tropomyosin and F-actin cables in vivo.
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Affiliation(s)
- Tomoyuki Hatano
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, Warwick CV4 7AL, UK
| | - Tzer Chyn Lim
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, Warwick CV4 7AL, UK
| | - Ingrid Billault-Chaumartin
- Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, Biophore Building, CH-1015 Lausanne, Switzerland
| | - Anubhav Dhar
- Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India
| | - Ying Gu
- The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
- Randall Centre for Cell and Molecular Biophysics, School of Basic and Medical Biosciences, King's College London, London, SE1 1UL, UK
| | - Teresa Massam-Wu
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, Warwick CV4 7AL, UK
| | - William Scott
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, Warwick CV4 7AL, UK
| | - Sushmitha Adishesha
- Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India
| | - Bernardo Chapa-y-Lazo
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, Warwick CV4 7AL, UK
| | - Luke Springall
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, Warwick CV4 7AL, UK
| | - Lavanya Sivashanmugam
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, Warwick CV4 7AL, UK
| | - Masanori Mishima
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, Warwick CV4 7AL, UK
| | - Sophie G. Martin
- Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, Biophore Building, CH-1015 Lausanne, Switzerland
| | - Snezhana Oliferenko
- The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
- Randall Centre for Cell and Molecular Biophysics, School of Basic and Medical Biosciences, King's College London, London, SE1 1UL, UK
| | - Saravanan Palani
- Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India
| | - Mohan K. Balasubramanian
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, Warwick CV4 7AL, UK
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16
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Abstract
Eukaryotic cells contain branched actin networks that are essential for endocytosis, motility, and other key cellular processes. These networks, which are formed by filamentous actin and the Arp2/3 complex, must subsequently be debranched to allow network remodeling and to recycle the Arp2/3 complex. Debranching appears to be catalyzed by two different members of the actin depolymerizing factor homology protein family: cofilin and glial maturation factor (GMF). However, their mechanisms of debranching are only partially understood. Here, we used single-molecule fluorescence imaging of Arp2/3 complex and actin filaments under physiological ionic conditions to observe debranching by GMF and cofilin. We demonstrate that cofilin, like GMF, is an authentic debrancher independent of its filament-severing activity and that the debranching activities of the two proteins are additive. While GMF binds directly to the Arp2/3 complex, cofilin selectively accumulates on branch-junction daughter filaments in tropomyosin-decorated networks just prior to debranching events. Quantitative comparison of debranching rates with the known kinetics of cofilin-actin binding suggests that cofilin occupancy of a particular single actin site at the branch junction is sufficient to trigger debranching. In rare cases in which the order of departure could be resolved during GMF- or cofilin-induced debranching, the Arp2/3 complex left the branch junction bound to the pointed end of the daughter filament, suggesting that both GMF and cofilin can work by destabilizing the mother filament-Arp2/3 complex interface. Taken together, these observations suggest that GMF and cofilin promote debranching by distinct yet complementary mechanisms.
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17
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Billault-Chaumartin I, Michon L, Anderson CA, Yde SE, Suarez C, Iwaszkiewicz J, Zoete V, Kovar DR, Martin SG. Actin assembly requirements of the formin Fus1 to build the fusion focus. J Cell Sci 2022; 135:275633. [PMID: 35673994 DOI: 10.1242/jcs.260289] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2022] [Accepted: 05/30/2022] [Indexed: 12/28/2022] Open
Abstract
In formin-family proteins, actin filament nucleation and elongation activities reside in the formin homology 1 (FH1) and FH2 domains, with reaction rates that vary by at least 20-fold between formins. Each cell expresses distinct formins that assemble one or several actin structures, raising the question of what confers each formin its specificity. Here, using the formin Fus1 in Schizosaccharomyces pombe, we systematically probed the importance of formin nucleation and elongation rates in vivo. Fus1 assembles the actin fusion focus, necessary for gamete fusion to form the zygote during sexual reproduction. By constructing chimeric formins with combinations of FH1 and FH2 domains previously characterized in vitro, we establish that changes in formin nucleation and elongation rates have direct consequences on fusion focus architecture, and that Fus1 native high nucleation and low elongation rates are optimal for fusion focus assembly. We further describe a point mutant in Fus1 FH2 that preserves native nucleation and elongation rates in vitro but alters function in vivo, indicating an additional FH2 domain property. Thus, rates of actin assembly are tailored for assembly of specific actin structures.
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Affiliation(s)
- Ingrid Billault-Chaumartin
- Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, Biophore building, CH-1015 Lausanne, Switzerland
| | - Laetitia Michon
- Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, Biophore building, CH-1015 Lausanne, Switzerland
| | - Caitlin A Anderson
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Sarah E Yde
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Cristian Suarez
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Justyna Iwaszkiewicz
- Molecular Modeling Group, Swiss Institute of Bioinformatics, Amphipôle Building, CH-1015 Lausanne, Switzerland
| | - Vincent Zoete
- Molecular Modeling Group, Swiss Institute of Bioinformatics, Amphipôle Building, CH-1015 Lausanne, Switzerland.,Department of Oncology UNIL-CHUV, University of Lausanne, Ludwig Institute for Cancer Research, Route de la Corniche 9A, CH-1066 Epalinges, Switzerland
| | - David R Kovar
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Sophie G Martin
- Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, Biophore building, CH-1015 Lausanne, Switzerland
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18
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Reindl T, Giese S, Greve JN, Reinke PY, Chizhov I, Latham SL, Mulvihill DP, Taft MH, Manstein DJ. Distinct actin–tropomyosin cofilament populations drive the functional diversification of cytoskeletal myosin motor complexes. iScience 2022; 25:104484. [PMID: 35720262 PMCID: PMC9204724 DOI: 10.1016/j.isci.2022.104484] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2022] [Revised: 05/02/2022] [Accepted: 05/24/2022] [Indexed: 11/02/2022] Open
Abstract
The effects of N-terminal acetylation of the high molecular weight tropomyosin isoforms Tpm1.6 and Tpm2.1 and the low molecular weight isoforms Tpm1.12, Tpm3.1, and Tpm4.2 on the actin affinity and the thermal stability of actin-tropomyosin cofilaments are described. Furthermore, we show how the exchange of cytoskeletal tropomyosin isoforms and their N-terminal acetylation affects the kinetic and chemomechanical properties of cytoskeletal actin-tropomyosin-myosin complexes. Our results reveal the extent to which the different actin-tropomyosin-myosin complexes differ in their kinetic and functional properties. The maximum sliding velocity of the actin filament as well as the optimal motor density for continuous unidirectional movement, parameters that were previously considered to be unique and invariant properties of each myosin isoform, are shown to be influenced by the exchange of the tropomyosin isoform and the N-terminal acetylation of tropomyosin. Tpm diversity is largely determined by sequences contributing to the overlap region Global sequence differences are of greater importance than variable exon 6 usage Tpm isoforms confer distinctly altered properties to cytoskeletal myosin motors Cytoskeletal myosins are differentially affected by N-terminal acetylation of Tpm
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19
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Jiang Y, Lu Q, Huang S. Functional non-equivalence of pollen ADF isovariants in Arabidopsis. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2022; 110:1068-1081. [PMID: 35233873 DOI: 10.1111/tpj.15723] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2021] [Revised: 02/24/2022] [Accepted: 02/26/2022] [Indexed: 06/14/2023]
Abstract
ADF/cofilin is a central regulator of actin dynamics. We previously demonstrated that two closely related Arabidopsis class IIa ADF isovariants, ADF7 and ADF10, are involved in the enhancement of actin turnover in pollen, but whether they have distinct functions remains unknown. Here, we further demonstrate that they exhibit distinct functions in regulating actin turnover both in vitro and in vivo. We found that ADF7 binds to ADP-G-actin with lower affinity, and severs and depolymerizes actin filaments less efficiently in vitro than ADF10. Accordingly, in pollen grains, ADF7 more extensively decorates actin filaments and is less freely distributed in the cytoplasm compared to ADF10. We further demonstrate that ADF7 and ADF10 show distinct intracellular localizations during pollen germination, and they have non-equivalent functions in promoting actin turnover in pollen. We thus propose that cooperation and labor division of ADF7 and ADF10 enable pollen cells to achieve exquisite control of the turnover of different actin structures to meet different cellular needs.
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Affiliation(s)
- Yuxiang Jiang
- Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Qiaonan Lu
- Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Shanjin Huang
- Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing, 100084, China
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20
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Boiero Sanders M, Toret CP, Guillotin A, Antkowiak A, Vannier T, Robinson RC, Michelot A. Specialization of actin isoforms derived from the loss of key interactions with regulatory factors. EMBO J 2022; 41:e107982. [PMID: 35178724 PMCID: PMC8886540 DOI: 10.15252/embj.2021107982] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2021] [Revised: 01/19/2022] [Accepted: 01/21/2022] [Indexed: 11/09/2022] Open
Abstract
A paradox of eukaryotic cells is that while some species assemble a complex actin cytoskeleton from a single ortholog, other species utilize a greater diversity of actin isoforms. The physiological consequences of using different actin isoforms, and the molecular mechanisms by which highly conserved actin isoforms are segregated into distinct networks, are poorly known. Here, we sought to understand how a simple biological system, composed of a unique actin and a limited set of actin‐binding proteins, reacts to a switch to heterologous actin expression. Using yeast as a model system and biomimetic assays, we show that such perturbation causes drastic reorganization of the actin cytoskeleton. Our results indicate that defective interaction of a heterologous actin for important regulators of actin assembly limits certain actin assembly pathways while reinforcing others. Expression of two heterologous actin variants, each specialized in assembling a different network, rescues cytoskeletal organization and confers resistance to external perturbation. Hence, while species using a unique actin have homeostatic actin networks, actin assembly pathways in species using several actin isoforms may act more independently.
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Affiliation(s)
| | - Christopher P Toret
- CNRS, IBDM, Turing Centre for Living Systems, Aix Marseille Univ, Marseille, France
| | - Audrey Guillotin
- CNRS, IBDM, Turing Centre for Living Systems, Aix Marseille Univ, Marseille, France
| | - Adrien Antkowiak
- CNRS, IBDM, Turing Centre for Living Systems, Aix Marseille Univ, Marseille, France
| | - Thomas Vannier
- CNRS, IBDM, Turing Centre for Living Systems, Aix Marseille Univ, Marseille, France
| | - Robert C Robinson
- Research Institute for Interdisciplinary Science (RIIS), Okayama University, Okayama, Japan.,School of Biomolecular Science and Engineering (BSE), Vidyasirimedhi Institute of Science and Technology (VISTEC), Rayong, Thailand
| | - Alphée Michelot
- CNRS, IBDM, Turing Centre for Living Systems, Aix Marseille Univ, Marseille, France
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21
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Abstract
The precise assembly and disassembly of actin filaments is required for several cellular processes, and their regulation has been scrutinized for decades. Twenty years ago, a handful of studies marked the advent of a new type of experiment to study actin dynamics: using optical microscopy to look at individual events, taking place on individual filaments in real time. Here, we summarize the main characteristics of this approach and how it has changed our ability to understand actin assembly dynamics. We also highlight some of its caveats and reflect on what we have learned over the past 20 years, leading us to propose a set of guidelines, which we hope will contribute to a better exploitation of this powerful tool.
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22
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Kadzik RS, Homa KE, Kovar DR. F-Actin Cytoskeleton Network Self-Organization Through Competition and Cooperation. Annu Rev Cell Dev Biol 2021; 36:35-60. [PMID: 33021819 DOI: 10.1146/annurev-cellbio-032320-094706] [Citation(s) in RCA: 55] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Many fundamental cellular processes such as division, polarization, endocytosis, and motility require the assembly, maintenance, and disassembly of filamentous actin (F-actin) networks at specific locations and times within the cell. The particular function of each network is governed by F-actin organization, size, and density as well as by its dynamics. The distinct characteristics of different F-actin networks are determined through the coordinated actions of specific sets of actin-binding proteins (ABPs). Furthermore, a cell typically assembles and uses multiple F-actin networks simultaneously within a common cytoplasm, so these networks must self-organize from a common pool of shared globular actin (G-actin) monomers and overlapping sets of ABPs. Recent advances in multicolor imaging and analysis of ABPs and their associated F-actin networks in cells, as well as the development of sophisticated in vitro reconstitutions of networks with ensembles of ABPs, have allowed the field to start uncovering the underlying principles by which cells self-organize diverse F-actin networks to execute basic cellular functions.
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Affiliation(s)
- Rachel S Kadzik
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637, USA; , .,Department of Molecular BioSciences, Northwestern University, Evanston, Illinois 60208, USA;
| | - Kaitlin E Homa
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637, USA; ,
| | - David R Kovar
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637, USA; , .,Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637, USA
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23
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Homa KE, Zsolnay V, Anderson CA, O'Connell ME, Neidt EM, Voth GA, Bidone TC, Kovar DR. Formin Cdc12's specific actin assembly properties are tailored for cytokinesis in fission yeast. Biophys J 2021; 120:2984-2997. [PMID: 34214524 DOI: 10.1016/j.bpj.2021.06.023] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Revised: 06/07/2021] [Accepted: 06/16/2021] [Indexed: 11/16/2022] Open
Abstract
Formins generate unbranched actin filaments by a conserved, processive actin assembly mechanism. Most organisms express multiple formin isoforms that mediate distinct cellular processes and facilitate actin filament polymerization by significantly different rates, but how these actin assembly differences correlate to cellular activity is unclear. We used a computational model of fission yeast cytokinetic ring assembly to test the hypothesis that particular actin assembly properties help tailor formins for specific cellular roles. Simulations run in different actin filament nucleation and elongation conditions revealed that variations in formin's nucleation efficiency critically impact both the probability and timing of contractile ring formation. To probe the physiological importance of nucleation efficiency, we engineered fission yeast formin chimera strains in which the FH1-FH2 actin assembly domains of full-length cytokinesis formin Cdc12 were replaced with the FH1-FH2 domains from functionally and evolutionarily diverse formins with significantly different actin assembly properties. Although Cdc12 chimeras generally support life in fission yeast, quantitative live-cell imaging revealed a range of cytokinesis defects from mild to severe. In agreement with the computational model, chimeras whose nucleation efficiencies are least similar to Cdc12 exhibit more severe cytokinesis defects, specifically in the rate of contractile ring assembly. Together, our computational and experimental results suggest that fission yeast cytokinesis is ideally mediated by a formin with properly tailored actin assembly parameters.
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Affiliation(s)
- Kaitlin E Homa
- Department of Molecular Genetics and Cell Biology, Chicago, Illinois
| | - Vilmos Zsolnay
- Graduate Program in Biophysical Sciences, Chicago, Illinois
| | | | | | - Erin M Neidt
- Department of Molecular Genetics and Cell Biology, Chicago, Illinois
| | - Gregory A Voth
- Department of Chemistry, The James Franck Institute, Institute for Biophysical Dynamics and Computation Institute, Chicago, Illinois
| | - Tamara C Bidone
- Department of Biomedical Engineering, Salt Lake City, Utah; Scientific Computing and Imaging Institute, University of Utah, Salt Lake City, Utah.
| | - David R Kovar
- Department of Molecular Genetics and Cell Biology, Chicago, Illinois; Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois.
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24
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Yan Y, Liu S, Hu C, Xie C, Zhao L, Wang S, Zhang W, Cheng Z, Gao J, Fu X, Yang Z, Wang X, Zhang J, Lin L, Shi A. RTKN-1/Rhotekin shields endosome-associated F-actin from disassembly to ensure endocytic recycling. J Cell Biol 2021; 220:211976. [PMID: 33844824 PMCID: PMC8047894 DOI: 10.1083/jcb.202007149] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Revised: 01/22/2021] [Accepted: 03/10/2021] [Indexed: 12/15/2022] Open
Abstract
Cargo sorting and the subsequent membrane carrier formation require a properly organized endosomal actin network. To better understand the actin dynamics during endocytic recycling, we performed a genetic screen in C. elegans and identified RTKN-1/Rhotekin as a requisite to sustain endosome-associated actin integrity. Loss of RTKN-1 led to a prominent decrease in actin structures and basolateral recycling defects. Furthermore, we showed that the presence of RTKN-1 thwarts the actin disassembly competence of UNC-60A/cofilin. Consistently, in RTKN-1–deficient cells, UNC-60A knockdown replenished actin structures and alleviated the recycling defects. Notably, an intramolecular interaction within RTKN-1 could mediate the formation of oligomers. Overexpression of an RTKN-1 mutant form that lacks self-binding capacity failed to restore actin structures and recycling flow in rtkn-1 mutants. Finally, we demonstrated that SDPN-1/Syndapin acts to direct the recycling endosomal dwelling of RTKN-1 and promotes actin integrity there. Taken together, these findings consolidated the role of SDPN-1 in organizing the endosomal actin network architecture and introduced RTKN-1 as a novel regulatory protein involved in this process.
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Affiliation(s)
- Yanling Yan
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Shuai Liu
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Can Hu
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Chaoyi Xie
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Linyue Zhao
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Shimin Wang
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Wenjuan Zhang
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Zihang Cheng
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Jinghu Gao
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Xin Fu
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Zhenrong Yang
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Xianghong Wang
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Jing Zhang
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Long Lin
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China.,Cell Architecture Research Institute, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Anbing Shi
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China.,Cell Architecture Research Institute, Huazhong University of Science and Technology, Wuhan, Hubei, China
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25
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Wioland H, Frémont S, Guichard B, Echard A, Jégou A, Romet-Lemonne G. Actin filament oxidation by MICAL1 suppresses protections from cofilin-induced disassembly. EMBO Rep 2021; 22:e50965. [PMID: 33393173 DOI: 10.15252/embr.202050965] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 11/18/2020] [Accepted: 11/27/2020] [Indexed: 02/01/2023] Open
Abstract
Proteins of the ADF/cofilin family play a central role in the disassembly of actin filaments, and their activity must be tightly regulated in cells. Recently, the oxidation of actin filaments by the enzyme MICAL1 was found to amplify the severing action of cofilin through unclear mechanisms. Using single filament experiments in vitro, we found that actin filament oxidation by MICAL1 increases, by several orders of magnitude, both cofilin binding and severing rates, explaining the dramatic synergy between oxidation and cofilin for filament disassembly. Remarkably, we found that actin oxidation bypasses the need for cofilin activation by dephosphorylation. Indeed, non-activated, phosphomimetic S3D-cofilin binds and severs oxidized actin filaments rapidly, in conditions where non-oxidized filaments are unaffected. Finally, tropomyosin Tpm1.8 loses its ability to protect filaments from cofilin severing activity when actin is oxidized by MICAL1. Together, our results show that MICAL1-induced oxidation of actin filaments suppresses their physiological protection from the action of cofilin. We propose that, in cells, direct post-translational modification of actin filaments by oxidation is a way to trigger their disassembly.
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Affiliation(s)
- Hugo Wioland
- Université de Paris, CNRS, Institut Jacques Monod, Paris, France
| | - Stéphane Frémont
- Membrane Traffic and Cell Division Lab, Institut Pasteur, UMR3691, CNRS, Paris, France
| | | | - Arnaud Echard
- Membrane Traffic and Cell Division Lab, Institut Pasteur, UMR3691, CNRS, Paris, France
| | - Antoine Jégou
- Université de Paris, CNRS, Institut Jacques Monod, Paris, France
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26
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Harris AR, Jreij P, Belardi B, Joffe AM, Bausch AR, Fletcher DA. Biased localization of actin binding proteins by actin filament conformation. Nat Commun 2020; 11:5973. [PMID: 33239610 PMCID: PMC7688639 DOI: 10.1038/s41467-020-19768-9] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Accepted: 10/30/2020] [Indexed: 11/09/2022] Open
Abstract
The assembly of actin filaments into distinct cytoskeletal structures plays a critical role in cell physiology, but how proteins localize differentially to these structures within a shared cytoplasm remains unclear. Here, we show that the actin-binding domains of accessory proteins can be sensitive to filament conformational changes. Using a combination of live cell imaging and in vitro single molecule binding measurements, we show that tandem calponin homology domains (CH1-CH2) can be mutated to preferentially bind actin networks at the front or rear of motile cells. We demonstrate that the binding kinetics of CH1-CH2 domain mutants varies as actin filament conformation is altered by perturbations that include stabilizing drugs and other binding proteins. These findings suggest that conformational changes of actin filaments in cells could help to direct accessory binding proteins to different actin cytoskeletal structures through a biophysical feedback loop.
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Affiliation(s)
- Andrew R Harris
- Department of Bioengineering and Biophysics Program, University of California, Berkeley, 648 Stanley Hall MC 1762, Berkeley, CA, 94720, USA
| | - Pamela Jreij
- Department of Bioengineering and Biophysics Program, University of California, Berkeley, 648 Stanley Hall MC 1762, Berkeley, CA, 94720, USA
| | - Brian Belardi
- Department of Bioengineering and Biophysics Program, University of California, Berkeley, 648 Stanley Hall MC 1762, Berkeley, CA, 94720, USA
| | - Aaron M Joffe
- Department of Bioengineering and Biophysics Program, University of California, Berkeley, 648 Stanley Hall MC 1762, Berkeley, CA, 94720, USA
| | - Andreas R Bausch
- Lehrstuhl für Biophysik (E27), Technische Universität München, Garching, 85748, Germany
| | - Daniel A Fletcher
- Department of Bioengineering and Biophysics Program, University of California, Berkeley, 648 Stanley Hall MC 1762, Berkeley, CA, 94720, USA.
- Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, 648 Stanley Hall MC 1762, Berkeley, CA, 94720, USA.
- Chan Zuckerberg Biohub, San Francisco, CA, 94158, USA.
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27
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Bareja I, Wioland H, Janco M, Nicovich PR, Jégou A, Romet-Lemonne G, Walsh J, Böcking T. Dynamics of Tpm1.8 domains on actin filaments with single-molecule resolution. Mol Biol Cell 2020; 31:2452-2462. [PMID: 32845787 PMCID: PMC7851853 DOI: 10.1091/mbc.e19-10-0586] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2019] [Revised: 08/19/2020] [Accepted: 08/21/2020] [Indexed: 01/28/2023] Open
Abstract
Tropomyosins regulate the dynamics and functions of the actin cytoskeleton by forming long chains along the two strands of actin filaments that act as gatekeepers for the binding of other actin-binding proteins. The fundamental molecular interactions underlying the binding of tropomyosin to actin are still poorly understood. Using microfluidics and fluorescence microscopy, we observed the binding of the fluorescently labeled tropomyosin isoform Tpm1.8 to unlabeled actin filaments in real time. This approach, in conjunction with mathematical modeling, enabled us to quantify the nucleation, assembly, and disassembly kinetics of Tpm1.8 on single filaments and at the single-molecule level. Our analysis suggests that Tpm1.8 decorates the two strands of the actin filament independently. Nucleation of a growing tropomyosin domain proceeds with high probability as soon as the first Tpm1.8 molecule is stabilized by the addition of a second molecule, ultimately leading to full decoration of the actin filament. In addition, Tpm1.8 domains are asymmetrical, with enhanced dynamics at the edge oriented toward the barbed end of the actin filament. The complete description of Tpm1.8 kinetics on actin filaments presented here provides molecular insight into actin-tropomyosin filament formation and the role of tropomyosins in regulating actin filament dynamics.
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Affiliation(s)
- Ilina Bareja
- EMBL Australia Node in Single Molecule Science and ARC Centre of Excellence in Advanced Molecular Imaging, School of Medical Sciences, UNSW Sydney, Sydney, NSW 2052, Australia
| | - Hugo Wioland
- Université de Paris, CNRS, Institut Jacques Monod, 75006 Paris, France
| | - Miro Janco
- EMBL Australia Node in Single Molecule Science and ARC Centre of Excellence in Advanced Molecular Imaging, School of Medical Sciences, UNSW Sydney, Sydney, NSW 2052, Australia
| | - Philip R. Nicovich
- EMBL Australia Node in Single Molecule Science and ARC Centre of Excellence in Advanced Molecular Imaging, School of Medical Sciences, UNSW Sydney, Sydney, NSW 2052, Australia
| | - Antoine Jégou
- Université de Paris, CNRS, Institut Jacques Monod, 75006 Paris, France
| | | | - James Walsh
- EMBL Australia Node in Single Molecule Science and ARC Centre of Excellence in Advanced Molecular Imaging, School of Medical Sciences, UNSW Sydney, Sydney, NSW 2052, Australia
| | - Till Böcking
- EMBL Australia Node in Single Molecule Science and ARC Centre of Excellence in Advanced Molecular Imaging, School of Medical Sciences, UNSW Sydney, Sydney, NSW 2052, Australia
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Garbett D, Bisaria A, Yang C, McCarthy DG, Hayer A, Moerner WE, Svitkina TM, Meyer T. T-Plastin reinforces membrane protrusions to bridge matrix gaps during cell migration. Nat Commun 2020; 11:4818. [PMID: 32968060 PMCID: PMC7511357 DOI: 10.1038/s41467-020-18586-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2020] [Accepted: 08/19/2020] [Indexed: 12/15/2022] Open
Abstract
Migrating cells move across diverse assemblies of extracellular matrix (ECM) that can be separated by micron-scale gaps. For membranes to protrude and reattach across a gap, actin filaments, which are relatively weak as single filaments, must polymerize outward from adhesion sites to push membranes towards distant sites of new adhesion. Here, using micropatterned ECMs, we identify T-Plastin, one of the most ancient actin bundling proteins, as an actin stabilizer that promotes membrane protrusions and enables bridging of ECM gaps. We show that T-Plastin widens and lengthens protrusions and is specifically enriched in active protrusions where F-actin is devoid of non-muscle myosin II activity. Together, our study uncovers critical roles of the actin bundler T-Plastin to promote protrusions and migration when adhesion is spatially-gapped. In vivo, cells migrate across a diverse landscape of extracellular matrix containing gaps which present a challenge for cells to protrude across. Here, the authors show that T-Plastin strengthens protrusive actin networks to promote protrusion, extracellular matrix gap-bridging, and cell migration.
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Affiliation(s)
- Damien Garbett
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA.
| | - Anjali Bisaria
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA
| | - Changsong Yang
- Department of Biology, University of Pennsylvania, Philadelphia, PA, USA
| | | | - Arnold Hayer
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA.,Department of Biology, McGill University, Montréal, Canada
| | - W E Moerner
- Department of Chemistry, Stanford University, Stanford, CA, USA
| | - Tatyana M Svitkina
- Department of Biology, University of Pennsylvania, Philadelphia, PA, USA
| | - Tobias Meyer
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA, USA. .,Department of Cell and Developmental Biology, Weill Cornell Medicine, New York, NY, USA.
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29
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Boiero Sanders M, Antkowiak A, Michelot A. Diversity from similarity: cellular strategies for assigning particular identities to actin filaments and networks. Open Biol 2020; 10:200157. [PMID: 32873155 PMCID: PMC7536088 DOI: 10.1098/rsob.200157] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The actin cytoskeleton has the particularity of being assembled into many functionally distinct filamentous networks from a common reservoir of monomeric actin. Each of these networks has its own geometrical, dynamical and mechanical properties, because they are capable of recruiting specific families of actin-binding proteins (ABPs), while excluding the others. This review discusses our current understanding of the underlying molecular mechanisms that cells have developed over the course of evolution to segregate ABPs to appropriate actin networks. Segregation of ABPs requires the ability to distinguish actin networks as different substrates for ABPs, which is regulated in three different ways: (1) by the geometrical organization of actin filaments within networks, which promotes or inhibits the accumulation of ABPs; (2) by the identity of the networks' filaments, which results from the decoration of actin filaments with additional proteins such as tropomyosin, from the use of different actin isoforms or from covalent modifications of actin; (3) by the existence of collaborative or competitive binding to actin filaments between two or multiple ABPs. This review highlights that all these effects need to be taken into account to understand the proper localization of ABPs in cells, and discusses what remains to be understood in this field of research.
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Affiliation(s)
- Micaela Boiero Sanders
- Aix Marseille University, CNRS, IBDM, Turing Centre for Living Systems, Marseille, France
| | - Adrien Antkowiak
- Aix Marseille University, CNRS, IBDM, Turing Centre for Living Systems, Marseille, France
| | - Alphée Michelot
- Aix Marseille University, CNRS, IBDM, Turing Centre for Living Systems, Marseille, France
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Palani S, Koester D, Balasubramanian MK. Phosphoregulation of tropomyosin-actin interaction revealed using a genetic code expansion strategy. Wellcome Open Res 2020; 5:161. [PMID: 32802966 PMCID: PMC7411518 DOI: 10.12688/wellcomeopenres.16082.1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/03/2020] [Indexed: 11/20/2022] Open
Abstract
Tropomyosins are coiled-coil proteins that regulate the stability and / or function of actin cytoskeleton in muscle and non-muscle cells through direct binding of actin filaments. Recently, using the fission yeast, we discovered a new mechanism by which phosphorylation of serine 125 of tropomyosin (Cdc8), reduced its affinity for actin filaments thereby providing access for the actin severing protein Adf1/Cofilin to actin filaments causing instability of actin filaments. Here we use a genetic code expansion strategy to directly examine this conclusion. We produced in Escherichia coli Cdc8-tropomyosin bearing a phosphate group on Serine-125 (Cdc8 PS125), using an orthogonal tRNA-tRNA synthetase pair that directly incorporates phosphoserine into proteins in response to a UAG codon in the corresponding mRNA. We show using total internal reflection (TIRF) microscopy that, whereas E.coli produced Cdc8 PS125 does not bind actin filaments, Cdc8 PS125 incubated with lambda phosphatase binds actin filaments. This work directly demonstrates that a phosphate moiety present on serine 125 leads to decreased affinity of Cdc8-tropomyosin for actin filaments. We also extend the work to demonstrate the usefulness of the genetic code expansion approach in imaging actin cytoskeletal components.
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Affiliation(s)
- Saravanan Palani
- Centre for Mechanochemical Cell Biology, Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, CV4 7AL, UK
| | - Darius Koester
- Centre for Mechanochemical Cell Biology, Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, CV4 7AL, UK
| | - Mohan K Balasubramanian
- Centre for Mechanochemical Cell Biology, Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, CV4 7AL, UK
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31
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Janco M, Dedova I, Bryce NS, Hardeman EC, Gunning PW. Visualizing the in vitro assembly of tropomyosin/actin filaments using TIRF microscopy. Biophys Rev 2020; 12:879-885. [PMID: 32638329 PMCID: PMC7429660 DOI: 10.1007/s12551-020-00720-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Accepted: 07/02/2020] [Indexed: 12/23/2022] Open
Abstract
Tropomyosins are elongated alpha-helical proteins that form co-polymers with most actin filaments within a cell and play important roles in the structural and functional diversification of the actin cytoskeleton. How the assembly of tropomyosins along an actin filament is regulated and the kinetics of tropomyosin association with an actin filament is yet to be fully determined. A recent series of publications have used total internal reflection fluorescence (TIRF) microscopy in combination with advanced surface and protein chemistry to visualise the molecular assembly of actin/tropomyosin filaments in vitro. Here, we review the use of the in vitro TIRF assay in the determination of kinetic data on tropomyosin filament assembly. This sophisticated approach has enabled generation of real-time single-molecule data to fill the gap between in vitro bulk assays and in vivo assays of tropomyosin function. The in vitro TIRF assays provide a new foundation for future studies involving multiple actin-binding proteins that will more accurately reflect the physiological protein-protein interactions in cells.
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Affiliation(s)
- Miro Janco
- School of Medical Sciences, University of New South Wales, Sydney, NSW, 2052, Australia
| | - Irina Dedova
- School of Medical Sciences, University of New South Wales, Sydney, NSW, 2052, Australia
| | - Nicole S Bryce
- School of Medical Sciences, University of New South Wales, Sydney, NSW, 2052, Australia
| | - Edna C Hardeman
- School of Medical Sciences, University of New South Wales, Sydney, NSW, 2052, Australia
| | - Peter W Gunning
- School of Medical Sciences, University of New South Wales, Sydney, NSW, 2052, Australia.
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32
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Pavadai E, Lehman W, Rynkiewicz MJ. Protein-Protein Docking Reveals Dynamic Interactions of Tropomyosin on Actin Filaments. Biophys J 2020; 119:75-86. [PMID: 32521240 DOI: 10.1016/j.bpj.2020.05.017] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Revised: 05/01/2020] [Accepted: 05/18/2020] [Indexed: 01/01/2023] Open
Abstract
Experimental approaches such as fiber diffraction and cryo-electron microscopy reconstruction have defined regulatory positions of tropomyosin on actin but have not, as yet, succeeded at determining key atomic-level contacts between these proteins or fully substantiated the dynamics of their interactions at a structural level. To overcome this deficiency, we have previously employed computational approaches to deduce global dynamics of thin filament components by energy landscape determination and molecular dynamics simulations. Still, these approaches remain computationally challenging for any complex and large macromolecular assembly like the thin filament. For example, tropomyosin cable wrapping around actin of thin filaments features both head-to-tail polymeric interactions and local twisting, both of which depart from strict superhelical symmetry. This produces a complex energy surface that is difficult to model and thus to evaluate globally. Therefore, at this stage of our understanding, assessing global molecular dynamics can prove to be inherently impractical. As an alternative, we adopted a "divide and conquer" protocol to investigate actin-tropomyosin interactions at an atomistic level. Here, we first employed unbiased protein-protein docking tools to identify binding specificity of individual tropomyosin pseudorepeat segments over the actin surface. Accordingly, tropomyosin "ligand" segments were rotated and translated over potential "target" binding sites on F-actin where the corresponding interaction energetics of billions of conformational poses were ranked by the programs PIPER and ClusPro. These data were used to assess favorable interactions and then to rebuild models of seamless and continuous tropomyosin cables over the F-actin substrate, which were optimized further by flexible fitting routines and molecular dynamics. The models generated azimuthally distinct regulatory positions for tropomyosin cables along thin filaments on actin dominated by stereo-specific head-to-tail overlap linkage. The outcomes are in good agreement with current cryo-electron microscopy topology and consistent with long-thought residue-to-residue interactions between actin and tropomyosin.
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Affiliation(s)
- Elumalai Pavadai
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts
| | - William Lehman
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts.
| | - Michael J Rynkiewicz
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts
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33
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Schwebach CL, Kudryashova E, Zheng W, Orchard M, Smith H, Runyan LA, Egelman EH, Kudryashov DS. Osteogenesis imperfecta mutations in plastin 3 lead to impaired calcium regulation of actin bundling. Bone Res 2020; 8:21. [PMID: 32509377 PMCID: PMC7244493 DOI: 10.1038/s41413-020-0095-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2019] [Revised: 02/06/2020] [Accepted: 03/23/2020] [Indexed: 12/11/2022] Open
Abstract
Mutations in actin-bundling protein plastin 3 (PLS3) emerged as a cause of congenital osteoporosis, but neither the role of PLS3 in bone development nor the mechanisms underlying PLS3-dependent osteoporosis are understood. Of the over 20 identified osteoporosis-linked PLS3 mutations, we investigated all five that are expected to produce full-length protein. One of the mutations distorted an actin-binding loop in the second actin-binding domain of PLS3 and abolished F-actin bundling as revealed by cryo-EM reconstruction and protein interaction assays. Surprisingly, the remaining four mutants fully retained F-actin bundling ability. However, they displayed defects in Ca2+ sensitivity: two of the mutants lost the ability to be inhibited by Ca2+, while the other two became hypersensitive to Ca2+. Each group of the mutants with similar biochemical properties showed highly characteristic cellular behavior. Wild-type PLS3 was distributed between lamellipodia and focal adhesions. In striking contrast, the Ca2+-hyposensitive mutants were not found at the leading edge but localized exclusively at focal adhesions/stress fibers, which displayed reinforced morphology. Consistently, the Ca2+-hypersensitive PLS3 mutants were restricted to lamellipodia, while chelation of Ca2+ caused their redistribution to focal adhesions. Finally, the bundling-deficient mutant failed to co-localize with any F-actin structures in cells despite a preserved F-actin binding through a non-mutation-bearing actin-binding domain. Our findings revealed that severe osteoporosis can be caused by a mutational disruption of the Ca2+-controlled PLS3's cycling between adhesion complexes and the leading edge. Integration of the structural, biochemical, and cell biology insights enabled us to propose a molecular mechanism of plastin activity regulation by Ca2+.
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Affiliation(s)
- Christopher L. Schwebach
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210 USA
- Molecular Cellular and Developmental Biology graduate program, The Ohio State University, Columbus, OH 43210 USA
| | - Elena Kudryashova
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210 USA
| | - Weili Zheng
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22908 USA
| | - Matthew Orchard
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210 USA
| | - Harper Smith
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210 USA
- Biophysics graduate program, The Ohio State University, Columbus, OH 43210 USA
| | - Lucas A. Runyan
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210 USA
| | - Edward H. Egelman
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22908 USA
| | - Dmitri S. Kudryashov
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210 USA
- Molecular Cellular and Developmental Biology graduate program, The Ohio State University, Columbus, OH 43210 USA
- Biophysics graduate program, The Ohio State University, Columbus, OH 43210 USA
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34
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Long-Range and Directional Allostery of Actin Filaments Plays Important Roles in Various Cellular Activities. Int J Mol Sci 2020; 21:ijms21093209. [PMID: 32370032 PMCID: PMC7246755 DOI: 10.3390/ijms21093209] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2020] [Revised: 04/27/2020] [Accepted: 04/30/2020] [Indexed: 12/18/2022] Open
Abstract
A wide variety of uniquely localized actin-binding proteins (ABPs) are involved in various cellular activities, such as cytokinesis, migration, adhesion, morphogenesis, and intracellular transport. In a micrometer-scale space such as the inside of cells, protein molecules diffuse throughout the cell interior within seconds. In this condition, how can ABPs selectively bind to particular actin filaments when there is an abundance of actin filaments in the cytoplasm? In recent years, several ABPs have been reported to induce cooperative conformational changes to actin filaments allowing structural changes to propagate along the filament cables uni- or bidirectionally, thereby regulating the subsequent binding of ABPs. Such propagation of ABP-induced cooperative conformational changes in actin filaments may be advantageous for the elaborate regulation of cellular activities driven by actin-based machineries in the intracellular space, which is dominated by diffusion. In this review, we focus on long-range allosteric regulation driven by cooperative conformational changes of actin filaments that are evoked by binding of ABPs, and discuss roles of allostery of actin filaments in narrow intracellular spaces.
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Mancl JM, Suarez C, Liang WG, Kovar DR, Tang WJ. Pseudomonas aeruginosa exoenzyme Y directly bundles actin filaments. J Biol Chem 2020; 295:3506-3517. [PMID: 32019868 DOI: 10.1074/jbc.ra119.012320] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2019] [Revised: 01/23/2020] [Indexed: 11/06/2022] Open
Abstract
Pseudomonas aeruginosa uses a type III secretion system (T3SS) to inject cytotoxic effector proteins into host cells. The promiscuous nucleotidyl cyclase, exoenzyme Y (ExoY), is one of the most common effectors found in clinical P. aeruginosa isolates. Recent studies have revealed that the nucleotidyl cyclase activity of ExoY is stimulated by actin filaments (F-actin) and that ExoY alters actin cytoskeleton dynamics in vitro, via an unknown mechanism. The actin cytoskeleton plays an important role in numerous key biological processes and is targeted by many pathogens to gain competitive advantages. We utilized total internal reflection fluorescence microscopy, bulk actin assays, and EM to investigate how ExoY impacts actin dynamics. We found that ExoY can directly bundle actin filaments with high affinity, comparable with eukaryotic F-actin-bundling proteins, such as fimbrin. Of note, ExoY enzymatic activity was not required for F-actin bundling. Bundling is known to require multiple actin-binding sites, yet small-angle X-ray scattering experiments revealed that ExoY is a monomer in solution, and previous data suggested that ExoY possesses only one actin-binding site. We therefore hypothesized that ExoY oligomerizes in response to F-actin binding and have used the ExoY structure to construct a dimer-based structural model for the ExoY-F-actin complex. Subsequent mutational analyses suggested that the ExoY oligomerization interface plays a crucial role in mediating F-actin bundling. Our results indicate that ExoY represents a new class of actin-binding proteins that modulate the actin cytoskeleton both directly, via F-actin bundling, and indirectly, via actin-activated nucleotidyl cyclase activity.
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Affiliation(s)
- Jordan M Mancl
- Ben May Department for Cancer Research, University of Chicago, Chicago, Illinois 60637
| | - Cristian Suarez
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois 60637
| | - Wenguang G Liang
- Ben May Department for Cancer Research, University of Chicago, Chicago, Illinois 60637
| | - David R Kovar
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois 60637
| | - Wei-Jen Tang
- Ben May Department for Cancer Research, University of Chicago, Chicago, Illinois 60637.
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Pollard LW, Garabedian MV, Alioto SL, Shekhar S, Goode BL. Genetically inspired in vitro reconstitution of Saccharomyces cerevisiae actin cables from seven purified proteins. Mol Biol Cell 2020; 31:335-347. [PMID: 31913750 PMCID: PMC7183793 DOI: 10.1091/mbc.e19-10-0576] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
A major goal of synthetic biology is to define the minimal cellular machinery required to assemble a biological structure in its simplest form. Here, we focused on Saccharomyces cerevisiae actin cables, which provide polarized tracks for intracellular transport and maintain defined lengths while continuously undergoing rapid assembly and turnover. Guided by the genetic requirements for proper cable assembly and dynamics, we show that seven evolutionarily conserved S. cerevisiae proteins (actin, formin, profilin, tropomyosin, capping protein, cofilin, and AIP1) are sufficient to reconstitute the formation of cables that undergo polarized turnover and maintain steady-state lengths similar to actin cables in vivo. Further, the removal of individual proteins from this simple in vitro reconstitution system leads to cable defects that closely approximate in vivo cable phenotypes caused by disrupting the corresponding genes. Thus, a limited set of molecular components is capable of self-organizing into dynamic, micron-scale actin structures with features similar to cables in living cells.
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Affiliation(s)
| | | | | | | | - Bruce L Goode
- Department of Biology, Brandeis University, Waltham, MA 02454
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37
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How Actin Tracks Affect Myosin Motors. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1239:183-197. [DOI: 10.1007/978-3-030-38062-5_9] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/08/2022]
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Holliday LS, de Faria LP, Rody WJ. Actin and Actin-Associated Proteins in Extracellular Vesicles Shed by Osteoclasts. Int J Mol Sci 2019; 21:ijms21010158. [PMID: 31881680 PMCID: PMC6981389 DOI: 10.3390/ijms21010158] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Revised: 12/16/2019] [Accepted: 12/16/2019] [Indexed: 02/07/2023] Open
Abstract
Extracellular vesicles (EVs) are shed by all eukaryotic cells and have emerged as important intercellular regulators. EVs released by osteoclasts were recently identified as important coupling factors in bone remodeling. They are shed as osteoclasts resorb bone and stimulate osteoblasts to form bone to replace the bone resorbed. We reported the proteomic content of osteoclast EVs with data from two-dimensional, high resolution liquid chromatography/mass spectrometry. In this article, we examine in detail the actin and actin-associated proteins found in osteoclast EVs. Like EVs from other cell types, actin and various actin-associated proteins were abundant. These include components of the polymerization machinery, myosin mechanoenzymes, proteins that stabilize or depolymerize microfilaments, and actin-associated proteins that are involved in regulating integrins. The selective incorporation of actin-associated proteins into osteoclast EVs suggests that they have roles in the formation of EVs and/or the regulatory signaling functions of the EVs. Regulating integrins so that they bind extracellular matrix tightly, in order to attach EVs to the extracellular matrix at specific locations in organs and tissues, is one potential active role for actin-associated proteins in EVs.
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Affiliation(s)
- L. Shannon Holliday
- Department of Orthodontics, College of Dentistry, University of Florida, Gainesville, FL 32610, USA
- Correspondence:
| | - Lorraine Perciliano de Faria
- Department of Biomaterials and Oral Biology, School of Dentistry, University of São Paulo, São Paulo 01000, Brazil;
| | - Wellington J. Rody
- Department of Orthodontics and Pediatric Dentistry, Stony Brook University School of Dental Medicine, Stony Brook, NY 11794, USA;
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Mechanical stiffness of reconstituted actin patches correlates tightly with endocytosis efficiency. PLoS Biol 2019; 17:e3000500. [PMID: 31652255 PMCID: PMC6834286 DOI: 10.1371/journal.pbio.3000500] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2019] [Revised: 11/06/2019] [Accepted: 10/18/2019] [Indexed: 01/16/2023] Open
Abstract
Clathrin-mediated endocytosis involves the sequential assembly of more than 60 proteins at the plasma membrane. An important fraction of these proteins regulates the assembly of an actin-related protein 2/3 (Arp2/3)-branched actin network, which is essential to generate the force during membrane invagination. We performed, on wild-type (WT) yeast and mutant strains lacking putative actin crosslinkers, a side-by-side comparison of in vivo endocytic phenotypes and in vitro rigidity measurements of reconstituted actin patches. We found a clear correlation between softer actin networks and a decreased efficiency of endocytosis. Our observations support a chain-of-consequences model in which loss of actin crosslinking softens Arp2/3-branched actin networks, directly limiting the transmission of the force. Additionally, the lifetime of failed endocytic patches increases, leading to a larger number of patches and a reduced pool of polymerizable actin, which slows down actin assembly and further impairs endocytosis. This study uses in vitro reconstitution of endocytic actin patches and mechanical measurements with chains of superparamagnetic microbeads to reveal a tight correlation between the stiffness of actin networks and the efficiency of endocytosis in yeast.
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Palani S, Köster DV, Hatano T, Kamnev A, Kanamaru T, Brooker HR, Hernandez-Fernaud JR, Jones AME, Millar JBA, Mulvihill DP, Balasubramanian MK. Phosphoregulation of tropomyosin is crucial for actin cable turnover and division site placement. J Cell Biol 2019; 218:3548-3559. [PMID: 31597679 PMCID: PMC6829654 DOI: 10.1083/jcb.201809089] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2018] [Revised: 11/29/2018] [Accepted: 08/30/2019] [Indexed: 02/05/2023] Open
Abstract
Palani et al. reveal a new mechanism by which the F-actin binding protein tropomyosin is regulated. They find that phosphorylation of tropomyosin reduces its affinity for F-actin, allowing the competing Adf1 to bind and sever actin filaments. Tropomyosin is a coiled-coil actin binding protein key to the stability of actin filaments. In muscle cells, tropomyosin is subject to calcium regulation, but its regulation in nonmuscle cells is not understood. Here, we provide evidence that the fission yeast tropomyosin, Cdc8, is regulated by phosphorylation of a serine residue. Failure of phosphorylation leads to an increased number and stability of actin cables and causes misplacement of the division site in certain genetic backgrounds. Phosphorylation of Cdc8 weakens its interaction with actin filaments. Furthermore, we show through in vitro reconstitution that phosphorylation-mediated release of Cdc8 from actin filaments facilitates access of the actin-severing protein Adf1 and subsequent filament disassembly. These studies establish that phosphorylation may be a key mode of regulation of nonmuscle tropomyosins, which in fission yeast controls actin filament stability and division site placement.
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Affiliation(s)
- Saravanan Palani
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, UK
| | - Darius V Köster
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, UK
| | - Tomoyuki Hatano
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, UK
| | - Anton Kamnev
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, UK
| | - Taishi Kanamaru
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, UK
| | - Holly R Brooker
- School of Biosciences, University of Kent, Canterbury, Kent, UK
| | | | | | - Jonathan B A Millar
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, UK
| | | | - Mohan K Balasubramanian
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, UK
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Billault-Chaumartin I, Martin SG. Capping Protein Insulates Arp2/3-Assembled Actin Patches from Formins. Curr Biol 2019; 29:3165-3176.e6. [PMID: 31495586 PMCID: PMC6864609 DOI: 10.1016/j.cub.2019.07.088] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2019] [Revised: 07/04/2019] [Accepted: 07/30/2019] [Indexed: 12/13/2022]
Abstract
How actin structures of distinct identities and functions coexist within the same environment is a critical self-organization question. Fission yeast cells have a simple actin cytoskeleton made of four structures: Arp2/3 assembles actin patches around endocytic pits, and the formins For3, Cdc12, and Fus1 assemble actin cables, the cytokinetic ring during division, and the fusion focus during sexual reproduction, respectively. The focus concentrates the delivery of hydrolases by myosin V to digest the cell wall for cell fusion. We discovered that cells lacking capping protein (CP), a heterodimer that blocks barbed-end dynamics and associates with actin patches, exhibit a delay in fusion. Consistent with CP-formin competition for barbed-end binding, Fus1, F-actin, and the linear filament marker tropomyosin hyper-accumulate at the fusion focus in cells lacking CP. CP deletion also rescues the fusion defect of a mutation in the Fus1 knob region. However, myosin V and exocytic cargoes are reduced at the fusion focus and diverted to ectopic foci, which underlies the fusion defect. Remarkably, the ectopic foci coincide with Arp2/3-assembled actin patches, which now contain low levels of Fus1. We further show that CP localization to actin patches is required to prevent the formation of ectopic foci and promote efficient cell fusion. During mitotic growth, actin patches lacking CP similarly display a dual identity, as they accumulate the formins For3 and Cdc12, normally absent from patches, and are co-decorated by the linear filament-binding protein tropomyosin and the patch marker fimbrin. Thus, CP serves to protect Arp2/3-nucleated structures from formin activity.
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Affiliation(s)
- Ingrid Billault-Chaumartin
- Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland
| | - Sophie G Martin
- Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland.
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42
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Mechanical and kinetic factors drive sorting of F-actin cross-linkers on bundles. Proc Natl Acad Sci U S A 2019; 116:16192-16197. [PMID: 31346091 DOI: 10.1073/pnas.1820814116] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In cells, actin-binding proteins (ABPs) sort to different regions to establish F-actin networks with diverse functions, including filopodia used for cell migration and contractile rings required for cell division. Recent experimental work uncovered a competition-based mechanism that may facilitate spatial localization of ABPs: binding of a short cross-linker protein to 2 actin filaments promotes the binding of other short cross-linkers and inhibits the binding of longer cross-linkers (and vice versa). We hypothesize this sorting arises because F-actin is semiflexible and cannot bend over short distances. We develop a mathematical theory and lattice models encompassing the most important physical parameters for this process and use coarse-grained simulations with explicit cross-linkers to characterize and test our predictions. Our theory and data predict an explicit dependence of cross-linker separation on bundle polymerization rate. We perform experiments that confirm this dependence, but with an unexpected cross-over in dominance of one cross-linker at high growth rates to the other at slow growth rates, and we investigate the origin of this cross-over with further simulations. The nonequilibrium mechanism that we describe can allow cells to organize molecular material to drive biological processes, and our results can guide the choice and design of cross-linkers for engineered protein-based materials.
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43
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Abstract
The shape of most animal cells is controlled by the actin cortex, a thin network of dynamic actin filaments (F-actin) situated just beneath the plasma membrane. The cortex is held far from equilibrium by both active stresses and polymer turnover: Molecular motors drive deformations required for cell morphogenesis, while actin-filament disassembly dynamics relax stress and facilitate cortical remodeling. While many aspects of actin-cortex mechanics are well characterized, a mechanistic understanding of how nonequilibrium actin turnover contributes to stress relaxation is still lacking. To address this, we developed a reconstituted in vitro system of entangled F-actin, wherein the steady-state length and turnover rate of F-actin are controlled by the actin regulatory proteins cofilin, profilin, and formin, which sever, recycle, and assemble filaments, respectively. Cofilin-mediated severing accelerates the turnover and spatial reorganization of F-actin, without significant changes to filament length. We demonstrate that cofilin-mediated severing is a single-timescale mode of stress relaxation that tunes the low-frequency viscosity over two orders of magnitude. These findings serve as the foundation for understanding the mechanics of more physiological F-actin networks with turnover and inform an updated microscopic model of single-filament turnover. They also demonstrate that polymer activity, in the form of ATP hydrolysis on F-actin coupled to nucleotide-dependent cofilin binding, is sufficient to generate a form of active matter wherein asymmetric filament disassembly preserves filament number despite sustained severing.
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44
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Christensen JR, Homa KE, Morganthaler AN, Brown RR, Suarez C, Harker AJ, O'Connell ME, Kovar DR. Cooperation between tropomyosin and α-actinin inhibits fimbrin association with actin filament networks in fission yeast. eLife 2019; 8:47279. [PMID: 31180322 PMCID: PMC6557641 DOI: 10.7554/elife.47279] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2019] [Accepted: 05/29/2019] [Indexed: 11/13/2022] Open
Abstract
We previously discovered that competition between fission yeast actin binding proteins (ABPs) for binding F-actin facilitates their sorting to different cellular networks. Specifically, competition between endocytic actin patch ABPs fimbrin Fim1 and cofilin Adf1 enhances their activities, and prevents tropomyosin Cdc8's association with actin patches. However, these interactions do not explain how Fim1 is prevented from associating strongly with other F-actin networks such as the contractile ring. Here, we identified α-actinin Ain1, a contractile ring ABP, as another Fim1 competitor. Fim1 competes with Ain1 for association with F-actin, which is dependent upon their F-actin residence time. While Fim1 outcompetes both Ain1 and Cdc8 individually, Cdc8 enhances the F-actin bundling activity of Ain1, allowing Ain1 to generate F-actin bundles that Cdc8 can bind in the presence of Fim1. Therefore, the combination of contractile ring ABPs Ain1 and Cdc8 is capable of inhibiting Fim1's association with F-actin networks.
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Affiliation(s)
- Jenna R Christensen
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States
| | - Kaitlin E Homa
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States
| | - Alisha N Morganthaler
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States
| | - Rachel R Brown
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States
| | - Cristian Suarez
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States
| | - Alyssa J Harker
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, United States
| | - Meghan E O'Connell
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States
| | - David R Kovar
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States.,Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, United States
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Sizes of actin networks sharing a common environment are determined by the relative rates of assembly. PLoS Biol 2019; 17:e3000317. [PMID: 31181075 PMCID: PMC6586355 DOI: 10.1371/journal.pbio.3000317] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Revised: 06/20/2019] [Accepted: 05/28/2019] [Indexed: 12/31/2022] Open
Abstract
Within the cytoplasm of a single cell, several actin networks can coexist with distinct sizes, geometries, and protein compositions. These actin networks assemble in competition for a limited pool of proteins present in a common cellular environment. To predict how two distinct networks of actin filaments control this balance, the simultaneous assembly of actin-related protein 2/3 (Arp2/3)-branched networks and formin-linear networks of actin filaments around polystyrene microbeads was investigated with a range of actin accessory proteins (profilin, capping protein, actin-depolymerizing factor [ADF]/cofilin, and tropomyosin). Accessory proteins generally affected actin assembly rates for the distinct networks differently. These effects at the scale of individual actin networks were surprisingly not always correlated with corresponding loss-of-function phenotypes in cells. However, our observations agreed with a global interpretation, which compared relative actin assembly rates of individual actin networks. This work supports a general model in which the size of distinct actin networks is determined by their relative capacity to assemble in a common and competing environment. A biomimetic assay using polystyrene beads compares the rates of actin assembly on linear and branched networks, revealing how the size of rival actin networks in cells is regulated by their relative capacity to assemble in a common environment.
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Torsional stress generated by ADF/cofilin on cross-linked actin filaments boosts their severing. Proc Natl Acad Sci U S A 2019; 116:2595-2602. [PMID: 30692249 PMCID: PMC6377502 DOI: 10.1073/pnas.1812053116] [Citation(s) in RCA: 63] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Actin filaments assemble into ordered networks able to exert forces and shape cells. In response, filaments are exposed to mechanical stress which can potentially modulate their interactions with regulatory proteins. We developed in vitro tools to manipulate single filaments and study the impact of mechanics on the activity of actin depolymerizing factor (ADF)/cofilin, the central player in actin disassembly. While tension has almost no effect, curvature enhances severing by ADF/cofilin. We also discovered a mechanism that boosts the severing of anchored filaments: When binding to these filaments, ADF/cofilin locally increases their natural helicity, generating a torque that accelerates filament fragmentation up to 100-fold. As a consequence, interconnected filament networks are severed far more efficiently than independent filaments. Proteins of the actin depolymerizing factor (ADF)/cofilin family are the central regulators of actin filament disassembly. A key function of ADF/cofilin is to sever actin filaments. However, how it does so in a physiological context, where filaments are interconnected and under mechanical stress, remains unclear. Here, we monitor and quantify the action of ADF/cofilin in different mechanical situations by using single-molecule, single-filament, and filament network techniques, coupled to microfluidics. We find that local curvature favors severing, while tension surprisingly has no effect on cofilin binding and weakly enhances severing. Remarkably, we observe that filament segments that are held between two anchoring points, thereby constraining their twist, experience a mechanical torque upon cofilin binding. We find that this ADF/cofilin-induced torque does not hinder ADF/cofilin binding, but dramatically enhances severing. A simple model, which faithfully recapitulates our experimental observations, indicates that the ADF/cofilin-induced torque increases the severing rate constant 100-fold. A consequence of this mechanism, which we verify experimentally, is that cross-linked filament networks are severed by cofilin far more efficiently than nonconnected filaments. We propose that this mechanochemical mechanism is critical to boost ADF/cofilin’s ability to sever highly connected filament networks in cells.
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47
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Jansen S, Goode BL. Tropomyosin isoforms differentially tune actin filament length and disassembly. Mol Biol Cell 2019; 30:671-679. [PMID: 30650006 PMCID: PMC6589703 DOI: 10.1091/mbc.e18-12-0815] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Cellular actin networks exhibit diverse filamentous architectures and turnover dynamics, but how these differences are specified remains poorly understood. Here, we used multicolor total internal reflection fluorescence microscopy to ask how decoration of actin filaments by five biologically prominent Tropomyosin (TPM) isoforms influences disassembly induced by Cofilin alone, or by the collaborative effects of Cofilin, Coronin, and AIP1 (CCA). TPM decoration restricted Cofilin binding to pointed ends, while not interfering with Coronin binding to filament sides. Different isoforms of TPM provided variable levels of protection against disassembly, with the strongest protection by Tpm3.1 and the weakest by Tpm1.6. In biomimetic assays in which filaments were simultaneously assembled by formins and disassembled by CCA, these TPM isoform-specific effects persisted, giving rise to filaments with different lengths and treadmilling behavior. Together, our data reveal that TPM isoforms have quantitatively distinct abilities to tune actin filament length and turnover.
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Affiliation(s)
- Silvia Jansen
- Department of Cell Biology and Physiology, Washington University in St. Louis, St. Louis, MO 63110
| | - Bruce L Goode
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA 02454
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48
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Matsuo T, Kono F, Fujiwara S. Effects of the cardiomyopathy-causing E244D mutation of troponin T on the structures of cardiac thin filaments studied by small-angle X-ray scattering. J Struct Biol 2018; 205:196-205. [PMID: 30599212 DOI: 10.1016/j.jsb.2018.12.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Revised: 12/07/2018] [Accepted: 12/10/2018] [Indexed: 02/04/2023]
Abstract
Small-angle X-ray scattering experiments were carried out to investigate the structural changes of cardiac thin filaments induced by the cardiomyopathy-causing E244D mutation in troponin T (TnT). We examined native thin filaments (NTF) from a bovine heart, reconstituted thin filaments containing human cardiac wild-type Tn (WTF), and filaments containing the E244D mutant of Tn (DTF), in the absence and presence of Ca2+. Analysis by model calculation showed that upon Ca2+-activation, tropomyosin (Tm) and Tn in the WTF and NTF moved together in a direction to expose myosin-binding sites on actin. On the other hand, Tm and Tn of the DTF moved in the opposite directions to each other upon Ca2+-activation. These movements caused Tm to expose more myosin-binding sites on actin than the WTF, suggesting that the affinity of myosin for actin is higher for the DTF. Thus, the mutation-induced structural changes in thin filaments would increase the number of myosin molecules bound to actin compared with the WTF, resulting in the force enhancement observed for the E244D mutation.
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Affiliation(s)
- Tatsuhito Matsuo
- Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology, 2-4 Shirakata, Tokai, Naka-Gun, Ibaraki 319-1106, Japan
| | - Fumiaki Kono
- Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology, 2-4 Shirakata, Tokai, Naka-Gun, Ibaraki 319-1106, Japan
| | - Satoru Fujiwara
- Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology, 2-4 Shirakata, Tokai, Naka-Gun, Ibaraki 319-1106, Japan.
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49
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Janco M, Böcking T, He S, Coster ACF. Interactions of tropomyosin Tpm1.1 on a single actin filament: A method for extraction and processing of high resolution TIRF microscopy data. PLoS One 2018; 13:e0208586. [PMID: 30532204 PMCID: PMC6287813 DOI: 10.1371/journal.pone.0208586] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2018] [Accepted: 11/20/2018] [Indexed: 12/14/2022] Open
Abstract
Skeletal muscle tropomyosin (Tpm1.1) is an elongated, rod-shaped, alpha-helical coiled-coil protein that forms continuous head-to-tail polymers along both sides of the actin filament. In this study we use single molecule fluorescence TIRF microscopy combined with a microfluidic device and fluorescently labelled proteins to measure Tpm1.1 association to and dissociation from single actin filaments. Our experimental setup allows us to clearly resolve Tpm1.1 interactions on both sides of the filaments. Here we provide a semi-automated method for the extraction and quantification of kymograph data for individual actin filaments bound at different Tpm1.1 concentrations. We determine boundaries on the kymograph on each side of the actin filament, based on intensity thresholding, performing fine manual editing of the boundaries (if needed) and extracting user defined kinetic properties of the system. Using our analytical tools we can determine (i) nucleation point(s) and rates, (ii) elongation rates of Tpm1.1, (iii) identify meeting points after the saturation of filament, and when dissociation occurs, (iv) initiation point(s), (v) the final dissociation point(s), as well as (vi) dissociation rates. All of these measurements can be extracted from both sides of the filament, allowing for the determination of possible differences in behaviour on the two sides of the filament, and across concentrations. The robust and repeatable nature of the method allows quantitative, semi-automated analyses to be made of large studies of acto-tropomyosin interactions, as well as for other actin binding proteins or filamentous structures, opening the way for dissection of the dynamics underlying these interactions.
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Affiliation(s)
- Miro Janco
- Single Molecule Science and ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, New South Wales, Australia
| | - Till Böcking
- Single Molecule Science and ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, New South Wales, Australia
| | - Stanley He
- School of Mathematics & Statistics, University of New South Wales, Sydney, New South Wales, Australia
| | - Adelle C. F. Coster
- School of Mathematics & Statistics, University of New South Wales, Sydney, New South Wales, Australia
- * E-mail:
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50
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Cheng C, Nowak RB, Amadeo MB, Biswas SK, Lo WK, Fowler VM. Tropomyosin 3.5 protects the F-actin networks required for tissue biomechanical properties. J Cell Sci 2018; 131:jcs222042. [PMID: 30333143 PMCID: PMC6288072 DOI: 10.1242/jcs.222042] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Accepted: 10/09/2018] [Indexed: 12/20/2022] Open
Abstract
Tropomyosins (Tpms) stabilize F-actin and regulate interactions with other actin-binding proteins. The eye lens changes shape in order to focus light to transmit a clear image, and thus lens organ function is tied to its biomechanical properties, presenting an opportunity to study Tpm functions in tissue mechanics. Mouse lenses contain Tpm3.5 (also known as TM5NM5), a previously unstudied isoform encoded by Tpm3, which is associated with F-actin on lens fiber cell membranes. Decreased levels of Tpm3.5 lead to softer and less mechanically resilient lenses that are unable to resume their original shape after compression. While cell organization and morphology appear unaffected, Tmod1 dissociates from the membrane in Tpm3.5-deficient lens fiber cells resulting in reorganization of the spectrin-F-actin and α-actinin-F-actin networks at the membrane. These rearranged F-actin networks appear to be less able to support mechanical load and resilience, leading to an overall change in tissue mechanical properties. This is the first in vivo evidence that a Tpm protein is essential for cell biomechanical stability in a load-bearing non-muscle tissue, and indicates that Tpm3.5 protects mechanically stable, load-bearing F-actin in vivoThis article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Catherine Cheng
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Roberta B Nowak
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Michael B Amadeo
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Sondip K Biswas
- Department of Neurobiology, Morehouse School of Medicine, Atlanta, GA 30314, USA
| | - Woo-Kuen Lo
- Department of Neurobiology, Morehouse School of Medicine, Atlanta, GA 30314, USA
| | - Velia M Fowler
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
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