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Demosthene B, Lee M, Marracino RR, Heidings JB, Kang EH. Molecular Basis for Actin Polymerization Kinetics Modulated by Solution Crowding. Biomolecules 2023; 13:biom13050786. [PMID: 37238656 DOI: 10.3390/biom13050786] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2023] [Revised: 04/18/2023] [Accepted: 04/25/2023] [Indexed: 05/28/2023] Open
Abstract
Actin polymerization drives cell movement and provides cells with structural integrity. Intracellular environments contain high concentrations of solutes, including organic compounds, macromolecules, and proteins. Macromolecular crowding has been shown to affect actin filament stability and bulk polymerization kinetics. However, the molecular mechanisms behind how crowding influences individual actin filament assembly are not well understood. In this study, we investigated how crowding modulates filament assembly kinetics using total internal reflection fluorescence (TIRF) microscopy imaging and pyrene fluorescence assays. The elongation rates of individual actin filaments analyzed from TIRF imaging depended on the type of crowding agent (polyethylene glycol, bovine serum albumin, and sucrose) as well as their concentrations. Further, we utilized all-atom molecular dynamics (MD) simulations to evaluate the effects of crowding molecules on the diffusion of actin monomers during filament assembly. Taken together, our data suggest that solution crowding can regulate actin assembly kinetics at the molecular level.
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Affiliation(s)
- Bryan Demosthene
- NanoScience Technology Center, University of Central Florida, Orlando, FL 32826, USA
- Burnett School of Biomedical Sciences, University of Central Florida, Orlando, FL 32827, USA
| | - Myeongsang Lee
- NanoScience Technology Center, University of Central Florida, Orlando, FL 32826, USA
| | - Ryan R Marracino
- NanoScience Technology Center, University of Central Florida, Orlando, FL 32826, USA
- Burnett School of Biomedical Sciences, University of Central Florida, Orlando, FL 32827, USA
| | - James B Heidings
- NanoScience Technology Center, University of Central Florida, Orlando, FL 32826, USA
- Burnett School of Biomedical Sciences, University of Central Florida, Orlando, FL 32827, USA
| | - Ellen Hyeran Kang
- NanoScience Technology Center, University of Central Florida, Orlando, FL 32826, USA
- Department of Physics, University of Central Florida, Orlando, FL 32816, USA
- Department of Materials Science and Engineering, University of Central Florida, Orlando, FL 32816, USA
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Lehne F, Pokrant T, Parbin S, Salinas G, Großhans J, Rust K, Faix J, Bogdan S. Calcium bursts allow rapid reorganization of EFhD2/Swip-1 cross-linked actin networks in epithelial wound closure. Nat Commun 2022; 13:2492. [PMID: 35524157 PMCID: PMC9076686 DOI: 10.1038/s41467-022-30167-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2021] [Accepted: 04/19/2022] [Indexed: 02/01/2023] Open
Abstract
Changes in cell morphology require the dynamic remodeling of the actin cytoskeleton. Calcium fluxes have been suggested as an important signal to rapidly relay information to the actin cytoskeleton, but the underlying mechanisms remain poorly understood. Here, we identify the EF-hand domain containing protein EFhD2/Swip-1 as a conserved lamellipodial protein strongly upregulated in Drosophila macrophages at the onset of metamorphosis when macrophage behavior shifts from quiescent to migratory state. Loss- and gain-of-function analysis confirm a critical function of EFhD2/Swip-1 in lamellipodial cell migration in fly and mouse melanoma cells. Contrary to previous assumptions, TIRF-analyses unambiguously demonstrate that EFhD2/Swip-1 proteins efficiently cross-link actin filaments in a calcium-dependent manner. Using a single-cell wounding model, we show that EFhD2/Swip-1 promotes wound closure in a calcium-dependent manner. Mechanistically, our data suggest that transient calcium bursts reduce EFhD2/Swip-1 cross-linking activity and thereby promote rapid reorganization of existing actin networks to drive epithelial wound closure.
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Affiliation(s)
- Franziska Lehne
- Institute of Physiology and Pathophysiology, Department of Molecular Cell Physiology, Philipps-University Marburg, Marburg, Germany
| | - Thomas Pokrant
- Institute for Biophysical Chemistry, Hannover Medical School, Hannover, Germany
| | - Sabnam Parbin
- NGS-Integrative Genomics Core Unit, Department of Human Genetics, University Medical Center Göttingen, Göttingen, Germany
| | - Gabriela Salinas
- NGS-Integrative Genomics Core Unit, Department of Human Genetics, University Medical Center Göttingen, Göttingen, Germany
| | - Jörg Großhans
- Department of Biology, Philipps-University Marburg, Marburg, Germany
| | - Katja Rust
- Institute of Physiology and Pathophysiology, Department of Molecular Cell Physiology, Philipps-University Marburg, Marburg, Germany
| | - Jan Faix
- Institute for Biophysical Chemistry, Hannover Medical School, Hannover, Germany
| | - Sven Bogdan
- Institute of Physiology and Pathophysiology, Department of Molecular Cell Physiology, Philipps-University Marburg, Marburg, Germany.
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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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Park J, Kravchuk P, Krishnaprasad A, Roy T, Kang EH. Graphene Enhances Actin Filament Assembly Kinetics and Modulates NIH-3T3 Fibroblast Cell Spreading. Int J Mol Sci 2022; 23:509. [PMID: 35008935 PMCID: PMC8745492 DOI: 10.3390/ijms23010509] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Revised: 12/28/2021] [Accepted: 12/30/2021] [Indexed: 01/01/2023] Open
Abstract
Actin plays critical roles in various cellular functions, including cell morphogenesis, differentiation, and movement. The assembly of actin monomers into double-helical filaments is regulated in surrounding microenvironments. Graphene is an attractive nanomaterial that has been used in various biomaterial applications, such as drug delivery cargo and scaffold for cells, due to its unique physical and chemical properties. Although several studies have shown the potential effects of graphene on actin at the cellular level, the direct influence of graphene on actin filament dynamics has not been studied. Here, we investigate the effects of graphene on actin assembly kinetics using spectroscopy and total internal reflection fluorescence microscopy. We demonstrate that graphene enhances the rates of actin filament growth in a concentration-dependent manner. Furthermore, cell morphology and spreading are modulated in mouse embryo fibroblast NIH-3T3 cultured on a graphene surface without significantly affecting cell viability. Taken together, these results suggest that graphene may have a direct impact on actin cytoskeleton remodeling.
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Affiliation(s)
- Jinho Park
- NanoScience Technology Center, University of Central Florida, Orlando, FL 32826, USA; (J.P.); (P.K.); (A.K.); (T.R.)
- Department of Materials Science and Engineering, University of Central Florida, Orlando, FL 32816, USA
| | - Pavlo Kravchuk
- NanoScience Technology Center, University of Central Florida, Orlando, FL 32826, USA; (J.P.); (P.K.); (A.K.); (T.R.)
| | - Adithi Krishnaprasad
- NanoScience Technology Center, University of Central Florida, Orlando, FL 32826, USA; (J.P.); (P.K.); (A.K.); (T.R.)
- Department of Electrical and Computer Engineering, University of Central Florida, Orlando, FL 32816, USA
| | - Tania Roy
- NanoScience Technology Center, University of Central Florida, Orlando, FL 32826, USA; (J.P.); (P.K.); (A.K.); (T.R.)
- Department of Materials Science and Engineering, University of Central Florida, Orlando, FL 32816, USA
- Department of Electrical and Computer Engineering, University of Central Florida, Orlando, FL 32816, USA
| | - Ellen Hyeran Kang
- NanoScience Technology Center, University of Central Florida, Orlando, FL 32826, USA; (J.P.); (P.K.); (A.K.); (T.R.)
- Department of Materials Science and Engineering, University of Central Florida, Orlando, FL 32816, USA
- Department of Physics, University of Central Florida, Orlando, FL 32816, USA
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Heidings JB, Demosthene B, Merlino TR, Castaneda N, Kang EH. Gelsolin-mediated actin filament severing in crowded environments. Biochem Biophys Res Commun 2020; 532:548-554. [PMID: 32900483 DOI: 10.1016/j.bbrc.2020.08.041] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Accepted: 08/15/2020] [Indexed: 10/24/2022]
Abstract
Gelsolin is a calcium-regulated actin binding protein that severs and caps actin filaments. Gelsolin's severing activity is important for regulating actin filament assembly dynamics that are required for cell motility as well as survival. The majority of in vitro studies of gelsolin have been performed in dilute buffer conditions which do not simulate the molecular interactions occurring in the crowded intracellular environment. We hypothesize that crowding results in greater gelsolin severing activity due to induced conformational changes in actin filaments and/or gelsolin. In this study, we evaluated the effects of crowding on gelsolin-mediated actin filament severing and gelsolin binding to actin filaments in crowded solutions, utilizing total internal reflection fluorescence (TIRF) microscopy and co-sedimentation assays. Our data indicates that the presence of crowders causes a decrease in the rate of gelsolin severing as well as a decrease in the amount of gelsolin bound to actin filaments, with greater effects caused by the polymeric crowder. Despite the severing rate decrease, gelsolin-mediated filament severing is increased in the presence of crowders. Understanding the crowding effect on gelsolin-mediated actin filament severing offers insight into the interactions between gelsolin and actin that occur inside the crowded cytoplasm.
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Affiliation(s)
- James B Heidings
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL, 32816, USA; NanoScience Technology Center, University of Central Florida, Orlando, FL, 32826, USA
| | - Bryan Demosthene
- NanoScience Technology Center, University of Central Florida, Orlando, FL, 32826, USA
| | - Theresa R Merlino
- NanoScience Technology Center, University of Central Florida, Orlando, FL, 32826, USA
| | - Nicholas Castaneda
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL, 32816, USA; NanoScience Technology Center, University of Central Florida, Orlando, FL, 32826, USA
| | - Ellen H Kang
- NanoScience Technology Center, University of Central Florida, Orlando, FL, 32826, USA; Department of Physics, University of Central Florida, Orlando, FL, 32816, USA; Department of Materials Science and Engineering, University of Central Florida, Orlando, FL, 32816, USA.
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Distinct VASP tetramers synergize in the processive elongation of individual actin filaments from clustered arrays. Proc Natl Acad Sci U S A 2017; 114:E5815-E5824. [PMID: 28667124 DOI: 10.1073/pnas.1703145114] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Ena/VASP proteins act as actin polymerases that drive the processive elongation of filament barbed ends in membrane protrusions or at the surface of bacterial pathogens. Based on previous analyses of fast and slow elongating VASP proteins by in vitro total internal reflection fluorescence microscopy (TIRFM) and kinetic and thermodynamic measurements, we established a kinetic model of Ena/VASP-mediated actin filament elongation. At steady state, it entails that tetrameric VASP uses one of its arms to processively track growing filament barbed ends while three G-actin-binding sites (GABs) on other arms are available to recruit and deliver monomers to the filament tip, suggesting that VASP operates as a single tetramer in solution or when clustered on a surface, albeit processivity and resistance toward capping protein (CP) differ dramatically between both conditions. Here, we tested the model by variation of the oligomerization state and by increase of the number of GABs on individual polypeptide chains. In excellent agreement with model predictions, we show that in solution the rates of filament elongation directly correlate with the number of free GABs. Strikingly, however, irrespective of the oligomerization state or presence of additional GABs, filament elongation on a surface invariably proceeded with the same rate as with the VASP tetramer, demonstrating that adjacent VASP molecules synergize in the elongation of a single filament. Additionally, we reveal that actin ATP hydrolysis is not required for VASP-mediated filament assembly. Finally, we show evidence for the requirement of VASP to form tetramers and provide an amended model of processive VASP-mediated actin assembly in clustered arrays.
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