1
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Singh A, Thutupalli S, Kumar M, Ameta S. Constrained dynamics of DNA oligonucleotides in phase-separated droplets. Biophys J 2024:S0006-3495(23)04178-4. [PMID: 38169216 DOI: 10.1016/j.bpj.2023.12.025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Revised: 12/20/2023] [Accepted: 12/28/2023] [Indexed: 01/05/2024] Open
Abstract
Understanding the dynamics of biomolecules in complex environments is crucial for elucidating the effect of condensed and heterogeneous environments on their functional properties. A relevant environment-and one that can also be mimicked easily in vitro-is that of phase-separated droplets. While phase-separated droplet systems have been shown to compartmentalize a wide range of functional biomolecules, the effects of internal structuration of droplets on the dynamics and mobility of internalized molecules remain poorly understood. Here, we use fluorescence correlation spectroscopy to measure the dynamics of short oligonucleotides encapsulated within two representative kinds of uncharged and charged phase-separated droplets. We find that the internal structuration controls the oligonucleotide dynamics in these droplets, revealed by measuring physical parameters at high spatiotemporal resolution. By varying oligonucleotide length and salt concentrations (and thereby charge screening), we found that the dynamics are significantly affected in the noncharged droplets compared to the charged system. Our work lays the foundation for unraveling and quantifying the physical parameters governing biomolecular transport in the condensed environment.
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Affiliation(s)
- Anupam Singh
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru, India
| | - Shashi Thutupalli
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru, India; International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bengaluru, India
| | - Manoj Kumar
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru, India.
| | - Sandeep Ameta
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru, India; Trivedi School of Biosciences, Ashoka University, Sonepat, India.
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2
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Singh G, George G, Raja SO, Kandaswamy P, Kumar M, Thutupalli S, Laxman S, Gulyani A. A molecular rotor FLIM probe reveals dynamic coupling between mitochondrial inner membrane fluidity and cellular respiration. Proc Natl Acad Sci U S A 2023; 120:e2213241120. [PMID: 37276406 PMCID: PMC10268597 DOI: 10.1073/pnas.2213241120] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Accepted: 04/13/2023] [Indexed: 06/07/2023] Open
Abstract
The inner mitochondrial membrane (IMM), housing components of the electron transport chain (ETC), is the site for respiration. The ETC relies on mobile carriers; therefore, it has long been argued that the fluidity of the densely packed IMM can potentially influence ETC flux and cell physiology. However, it is unclear if cells temporally modulate IMM fluidity upon metabolic or other stimulation. Using a photostable, red-shifted, cell-permeable molecular-rotor, Mitorotor-1, we present a multiplexed approach for quantitatively mapping IMM fluidity in living cells. This reveals IMM fluidity to be linked to cellular-respiration and responsive to stimuli. Multiple approaches combining in vitro experiments and live-cell fluorescence (FLIM) lifetime imaging microscopy (FLIM) show Mitorotor-1 to robustly report IMM 'microviscosity'/fluidity through changes in molecular free volume. Interestingly, external osmotic stimuli cause controlled swelling/compaction of mitochondria, thereby revealing a graded Mitorotor-1 response to IMM microviscosity. Lateral diffusion measurements of IMM correlate with microviscosity reported via Mitorotor-1 FLIM-lifetime, showing convergence of independent approaches for measuring IMM local-order. Mitorotor-1 FLIM reveals mitochondrial heterogeneity in IMM fluidity; between-and-within cells and across single mitochondrion. Multiplexed FLIM lifetime imaging of Mitorotor-1 and NADH autofluorescence reveals that IMM fluidity positively correlates with respiration, across individual cells. Remarkably, we find that stimulating respiration, through nutrient deprivation or chemically, also leads to increase in IMM fluidity. These data suggest that modulating IMM fluidity supports enhanced respiratory flux. Our study presents a robust method for measuring IMM fluidity and suggests a dynamic regulatory paradigm of modulating IMM local order on changing metabolic demand.
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Affiliation(s)
- Gaurav Singh
- Institute for Stem Cell Science and Regenerative Medicine, 560065Bangalore, India
| | - Geen George
- Institute for Stem Cell Science and Regenerative Medicine, 560065Bangalore, India
| | - Sufi O. Raja
- Department of Biochemistry, School of Life Sciences, University of Hyderabad, 500046Hyderabad, India
| | - Ponnuvel Kandaswamy
- Institute for Stem Cell Science and Regenerative Medicine, 560065Bangalore, India
| | - Manoj Kumar
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, 560065Bangalore, India
| | - Shashi Thutupalli
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, 560065Bangalore, India
- International Centre for Theoretical Sciences, Tata Institute for Fundamental Research, 560089 Bangalore, India
| | - Sunil Laxman
- Institute for Stem Cell Science and Regenerative Medicine, 560065Bangalore, India
| | - Akash Gulyani
- Institute for Stem Cell Science and Regenerative Medicine, 560065Bangalore, India
- Department of Biochemistry, School of Life Sciences, University of Hyderabad, 500046Hyderabad, India
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3
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Ameta S, Kumar M, Chakraborty N, Matsubara YJ, S P, Gandavadi D, Thutupalli S. Multispecies autocatalytic RNA reaction networks in coacervates. Commun Chem 2023; 6:91. [PMID: 37156998 PMCID: PMC10167250 DOI: 10.1038/s42004-023-00887-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Accepted: 04/19/2023] [Indexed: 05/10/2023] Open
Abstract
Robust localization of self-reproducing autocatalytic chemistries is a key step in the realization of heritable and evolvable chemical systems. While autocatalytic chemical reaction networks already possess attributes such as heritable self-reproduction and evolvability, localizing functional multispecies networks within complex primitive phases, such as coacervates, has remained unexplored. Here, we show the self-reproduction of the Azoarcus ribozyme system within charge-rich coacervates where catalytic ribozymes are produced by the autocatalytic assembly of constituent smaller RNA fragments. We systematically demonstrate the catalytic assembly of active ribozymes within phase-separated coacervates-both in micron-sized droplets as well as in a coalesced macrophase, underscoring the facility of the complex, charge-rich phase to support these reactions in multiple configurations. By constructing multispecies reaction networks, we show that these newly assembled molecules are active, participating both in self- and cross-catalysis within the coacervates. Finally, due to differential molecular transport, these phase-separated compartments endow robustness to the composition of the collectively autocatalytic networks against external perturbations. Altogether, our results establish the formation of multispecies self-reproducing reaction networks in phase-separated compartments which in turn render transient robustness to the network composition.
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Affiliation(s)
- Sandeep Ameta
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru, Karnataka, India.
- Trivedi School of Biosciences, Ashoka University, Plot No. 2, Rajiv Gandhi Education City, P.O. Rai, Sonepat, Haryana, 131029, India.
| | - Manoj Kumar
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru, Karnataka, India
| | - Nayan Chakraborty
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru, Karnataka, India
| | - Yoshiya J Matsubara
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru, Karnataka, India
| | - Prashanth S
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru, Karnataka, India
| | - Dhanush Gandavadi
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru, Karnataka, India
| | - Shashi Thutupalli
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru, Karnataka, India.
- International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bengaluru, Karnataka, India.
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4
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Baranov MV, Ioannidis M, Balahsioui S, Boersma A, de Boer R, Kumar M, Niwa M, Hirayama T, Zhou Q, Hopkins TM, Grijpstra P, Thutupalli S, Sacanna S, van den Bogaart G. Irregular particle morphology and membrane rupture facilitate ion gradients in the lumen of phagosomes. Biophys Rep (N Y) 2022; 2:100069. [PMID: 36425330 PMCID: PMC9680789 DOI: 10.1016/j.bpr.2022.100069] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/19/2022] [Accepted: 08/08/2022] [Indexed: 06/16/2023]
Abstract
Localized fluxes, production, and/or degradation coupled to limited diffusion are well known to result in stable spatial concentration gradients of biomolecules in the cell. In this study, we demonstrate that this also holds true for small ions, since we found that the close membrane apposition between the membrane of a phagosome and the surface of the cargo particle it encloses, together with localized membrane rupture, suffice for stable gradients of protons and iron cations within the lumen of the phagosome. Our data show that, in phagosomes containing hexapod-shaped silica colloid particles, the phagosomal membrane is ruptured at the positions of the tips of the rods, but not at other positions. This results in the confined leakage at these positions of protons and iron from the lumen of the phagosome into the cytosol. In contrast, acidification and iron accumulation still occur at the positions of the phagosomes nearer to the cores of the particles. Our study strengthens the concept that coupling metabolic and signaling reaction cascades can be spatially confined by localized limited diffusion.
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Affiliation(s)
- Maksim V. Baranov
- Department of Molecular Immunology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, Netherlands
| | - Melina Ioannidis
- Department of Molecular Immunology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, Netherlands
| | - Sami Balahsioui
- Department of Molecular Immunology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, Netherlands
| | - Auke Boersma
- Department of Molecular Immunology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, Netherlands
| | - Rinse de Boer
- Department of Molecular Immunology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, Netherlands
| | - Manoj Kumar
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India
| | - Masato Niwa
- Laboratory of Pharmaceutical and Medicinal Chemistry, Gifu Pharmaceutical University, 1–25–4, Daigaku-nishi, Gifu 201–1196, Japan
| | - Tasuku Hirayama
- Laboratory of Pharmaceutical and Medicinal Chemistry, Gifu Pharmaceutical University, 1–25–4, Daigaku-nishi, Gifu 201–1196, Japan
| | - Qintian Zhou
- Molecular Design Institute, Department of Chemistry, New York University, New York, NY, United States
| | - Terrence M. Hopkins
- Molecular Design Institute, Department of Chemistry, New York University, New York, NY, United States
| | - Pieter Grijpstra
- Department of Molecular Immunology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, Netherlands
| | - Shashi Thutupalli
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India
- nternational Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bangalore, India
| | - Stefano Sacanna
- Molecular Design Institute, Department of Chemistry, New York University, New York, NY, United States
| | - Geert van den Bogaart
- Department of Molecular Immunology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, Netherlands
- Department of Medical Biology and Pathology, University Medical Center Groningen, Groningen, Netherlands
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5
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Banerjee JP, Mandal R, Banerjee DS, Thutupalli S, Rao M. Unjamming and emergent nonreciprocity in active ploughing through a compressible viscoelastic fluid. Nat Commun 2022; 13:4533. [PMID: 35927258 PMCID: PMC9352703 DOI: 10.1038/s41467-022-31984-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2021] [Accepted: 07/08/2022] [Indexed: 11/09/2022] Open
Abstract
A dilute suspension of active Brownian particles in a dense compressible viscoelastic fluid, forms a natural setting to study the emergence of nonreciprocity during a dynamical phase transition. At these densities, the transport of active particles is strongly influenced by the passive medium and shows a dynamical jamming transition as a function of activity and medium density. In the process, the compressible medium is actively churned up - for low activity, the active particle gets self-trapped in a cavity of its own making, while for large activity, the active particle ploughs through the medium, either accompanied by a moving anisotropic wake, or leaving a porous trail. A hydrodynamic approach makes it evident that the active particle generates a long-range density wake which breaks fore-aft symmetry, consistent with the simulations. Accounting for the back-reaction of the compressible medium leads to (i) dynamical jamming of the active particle, and (ii) a dynamical non-reciprocal attraction between two active particles moving along the same direction, with the trailing particle catching up with the leading one in finite time. We emphasize that these nonreciprocal effects appear only when the active particles are moving and so manifest in the vicinity of the jamming-unjamming transition.
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Affiliation(s)
- Jyoti Prasad Banerjee
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences (TIFR), Bangalore, India
| | - Rituparno Mandal
- Institute for Theoretical Physics, Georg-August-Universität Göttingen, 37077, Göttingen, Germany
| | | | - Shashi Thutupalli
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences (TIFR), Bangalore, India. .,International Centre for Theoretical Sciences (TIFR), Bangalore, India.
| | - Madan Rao
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences (TIFR), Bangalore, India.
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6
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Thutupalli S. Depletion-Force Measurements Get Active. Physics 2022. [DOI: 10.1103/physics.15.113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/10/2022]
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7
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Kumar M, Singh A, Del Secco B, Baranov MV, van den Bogaart G, Sacanna S, Thutupalli S. Assembling anisotropic colloids using curvature-mediated lipid sorting. Soft Matter 2022; 18:1757-1766. [PMID: 35072193 DOI: 10.1039/d1sm01517f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
The use of colloid supported lipid bilayers (CSLBs) for assembling colloidal structures has been of recent interest. Here, we use multi-component lipid bilayer membranes formed around anisotropic colloids and show that the curvature anisotropy of the colloids drives a sorting of the lipids in the membrane along the colloids. We then exploit this curvature-sensitive lipid sorting to create "shape-anisotropic patchy colloids" - specifically, we use colloids with six rods sticking out of a central cubic core, "hexapods", for this purpose and demonstrate that membrane patches self-assemble at the tip of each of the six colloidal rods. The membrane patches are rendered sticky using biotinylated lipids in complement with a biotin-binding streptavidin protein. Finally, using these "shape-anisotropic patchy colloids", we demonstrate the directed assembly of colloidal links, paving the way for the creation of heterogeneous and flexible colloidal structures.
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Affiliation(s)
- Manoj Kumar
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India.
| | - Anupam Singh
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India.
| | - Benedetta Del Secco
- Molecular Design Institute, Department of Chemistry, New York University, New York, NY, USA
| | - Maksim V Baranov
- Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, The Netherlands
| | - Geert van den Bogaart
- Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, The Netherlands
| | - Stefano Sacanna
- Molecular Design Institute, Department of Chemistry, New York University, New York, NY, USA
| | - Shashi Thutupalli
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India.
- International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bangalore, India
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8
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Abstract
We study the collective dynamics of groups of whirligig beetles Dineutus discolor (Coleoptera: Gyrinidae) swimming freely on the surface of water. We extract individual trajectories for each beetle, including positions and orientations, and use this to discover (i) a density-dependent speed scaling like v ∼ ρ-ν with ν ≈ 0.4 over two orders of magnitude in density (ii) an inertial delay for velocity alignment of approximately 13 ms and (iii) coexisting high and low-density phases, consistent with motility-induced phase separation (MIPS). We modify a standard active Brownian particle (ABP) model to a corralled ABP (CABP) model that functions in open space by incorporating a density-dependent reorientation of the beetles, towards the cluster. We use our new model to test our hypothesis that an motility-induced phase separation (MIPS) (or a MIPS like effect) can explain the co-occurrence of high- and low-density phases we see in our data. The fitted model then successfully recovers a MIPS-like condensed phase for N = 200 and the absence of such a phase for smaller group sizes N = 50, 100.
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Affiliation(s)
- Harvey L Devereux
- Department of Mathematics, University of Warwick, Coventry CV4 7AL, UK.,Simons Center for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore 560065, India
| | - Colin R Twomey
- Department of Biology, and Mind Center for Outreach, Research and Education, University of Pennsylvania, Philadelphia, PA, USA
| | - Matthew S Turner
- Department of Physics, University of Warwick, Coventry CV4 7AL, UK.,Centre for Complexity Science, University of Warwick, Coventry CV4 7AL, UK.,Department of Chemical Engineering, Kyoto University, Kyoto 615-8510, Japan
| | - Shashi Thutupalli
- Simons Center for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore 560065, India.,International Centre for Theoretical Sciences, Tata Institute for Fundamental Research, Bangalore 560089, India
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9
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Ameta S, Matsubara YJ, Chakraborty N, Krishna S, Thutupalli S. Self-Reproduction and Darwinian Evolution in Autocatalytic Chemical Reaction Systems. Life (Basel) 2021; 11:308. [PMID: 33916135 PMCID: PMC8066523 DOI: 10.3390/life11040308] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2021] [Revised: 03/25/2021] [Accepted: 03/27/2021] [Indexed: 11/18/2022] Open
Abstract
Understanding the emergence of life from (primitive) abiotic components has arguably been one of the deepest and yet one of the most elusive scientific questions. Notwithstanding the lack of a clear definition for a living system, it is widely argued that heredity (involving self-reproduction) along with compartmentalization and metabolism are key features that contrast living systems from their non-living counterparts. A minimal living system may be viewed as "a self-sustaining chemical system capable of Darwinian evolution". It has been proposed that autocatalytic sets of chemical reactions (ACSs) could serve as a mechanism to establish chemical compositional identity, heritable self-reproduction, and evolution in a minimal chemical system. Following years of theoretical work, autocatalytic chemical systems have been constructed experimentally using a wide variety of substrates, and most studies, thus far, have focused on the demonstration of chemical self-reproduction under specific conditions. While several recent experimental studies have raised the possibility of carrying out some aspects of experimental evolution using autocatalytic reaction networks, there remain many open challenges. In this review, we start by evaluating theoretical studies of ACSs specifically with a view to establish the conditions required for such chemical systems to exhibit self-reproduction and Darwinian evolution. Then, we follow with an extensive overview of experimental ACS systems and use the theoretically established conditions to critically evaluate these empirical systems for their potential to exhibit Darwinian evolution. We identify various technical and conceptual challenges limiting experimental progress and, finally, conclude with some remarks about open questions.
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Affiliation(s)
- Sandeep Ameta
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Yoshiya J. Matsubara
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Nayan Chakraborty
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Sandeep Krishna
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Shashi Thutupalli
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
- International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bangalore 560089, India
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10
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Baranov MV, Kumar M, Sacanna S, Thutupalli S, van den Bogaart G. Modulation of Immune Responses by Particle Size and Shape. Front Immunol 2021; 11:607945. [PMID: 33679696 PMCID: PMC7927956 DOI: 10.3389/fimmu.2020.607945] [Citation(s) in RCA: 99] [Impact Index Per Article: 33.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2020] [Accepted: 12/23/2020] [Indexed: 12/12/2022] Open
Abstract
The immune system has to cope with a wide range of irregularly shaped pathogens that can actively move (e.g., by flagella) and also dynamically remodel their shape (e.g., transition from yeast-shaped to hyphal fungi). The goal of this review is to draw general conclusions of how the size and geometry of a pathogen affect its uptake and processing by phagocytes of the immune system. We compared both theoretical and experimental studies with different cells, model particles, and pathogenic microbes (particularly fungi) showing that particle size, shape, rigidity, and surface roughness are important parameters for cellular uptake and subsequent immune responses, particularly inflammasome activation and T cell activation. Understanding how the physical properties of particles affect immune responses can aid the design of better vaccines.
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Affiliation(s)
- Maksim V. Baranov
- Department of Molecular Immunology and Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, Netherlands
| | - Manoj Kumar
- Simons Center for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore, India
| | - Stefano Sacanna
- Molecular Design Institute, Department of Chemistry, New York University, New York, NY, United States
| | - Shashi Thutupalli
- Simons Center for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore, India
- International Centre for Theoretical Sciences, Tata Institute for Fundamental Research, Bangalore, India
| | - Geert van den Bogaart
- Department of Molecular Immunology and Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, Netherlands
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11
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Samhita L, K Raval P, Stephenson G, Thutupalli S, Agashe D. The impact of mistranslation on phenotypic variability and fitness. Evolution 2021; 75:1201-1217. [PMID: 33491193 PMCID: PMC8248024 DOI: 10.1111/evo.14179] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 10/25/2020] [Accepted: 12/20/2020] [Indexed: 01/20/2023]
Abstract
Phenotypic variation is widespread in natural populations, and can significantly alter population ecology and evolution. Phenotypic variation often reflects underlying genetic variation, but also manifests via non-heritable mechanisms. For instance, translation errors result in about 10% of cellular proteins carrying altered sequences. Thus, proteome diversification arising from translation errors can potentially generate phenotypic variability, in turn increasing variability in the fate of cells or of populations. However, the link between protein diversity and phenotypic variability remains unverified. We manipulated mistranslation levels in Escherichia coli, and measured phenotypic variability between single cells (individual-level variation), as well as replicate populations (population-level variation). Monitoring growth and survival, we find that mistranslation indeed increases variation across E. coli cells, but does not consistently increase variability in growth parameters across replicate populations. Interestingly, although any deviation from the wild-type (WT) level of mistranslation reduces fitness in an optimal environment, the increased variation is associated with a survival benefit under stress. Hence, we suggest that mistranslation-induced phenotypic variation can impact growth and survival and has the potential to alter evolutionary trajectories.
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Affiliation(s)
- Laasya Samhita
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India
| | - Parth K Raval
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India
| | - Godwin Stephenson
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India
| | - Shashi Thutupalli
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India.,International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bangalore, India
| | - Deepa Agashe
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India
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12
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Liu G, Patch A, Bahar F, Yllanes D, Welch RD, Marchetti MC, Thutupalli S, Shaevitz JW. Self-Driven Phase Transitions Drive Myxococcus xanthus Fruiting Body Formation. Phys Rev Lett 2019; 122:248102. [PMID: 31322369 DOI: 10.1103/physrevlett.122.248102] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Indexed: 06/10/2023]
Abstract
Combining high-resolution single cell tracking experiments with numerical simulations, we show that starvation-induced fruiting body formation in Myxococcus xanthus is a phase separation driven by cells that tune their motility over time. The phase separation can be understood in terms of cell density and a dimensionless Péclet number that captures cell motility through speed and reversal frequency. Our work suggests that M. xanthus takes advantage of a self-driven nonequilibrium phase transition that can be controlled at the single cell level.
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Affiliation(s)
- Guannan Liu
- Joseph Henry Laboratories of Physics and Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey 08544, USA
| | - Adam Patch
- Department of Physics and Soft and Living Matter Program, Syracuse University, Syracuse, New York 13244, USA
| | - Fatmagül Bahar
- Department of Biology, Syracuse University, Syracuse, New York 13244, USA
| | - David Yllanes
- Department of Physics and Soft and Living Matter Program, Syracuse University, Syracuse, New York 13244, USA
- Instituto de Biocomputación y Física de Sistemas Complejos (BIFI), 50009 Zaragoza, Spain
| | - Roy D Welch
- Department of Biology, Syracuse University, Syracuse, New York 13244, USA
| | - M Cristina Marchetti
- Department of Physics, University of California Santa Barbara, Santa Barbara, California 93106, USA
| | - Shashi Thutupalli
- Simons Center for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore 560065, India
| | - Joshua W Shaevitz
- Joseph Henry Laboratories of Physics and Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey 08544, USA
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13
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Olmi S, Martens EA, Thutupalli S, Torcini A. Intermittent chaotic chimeras for coupled rotators. Phys Rev E Stat Nonlin Soft Matter Phys 2015; 92:030901. [PMID: 26465413 DOI: 10.1103/physreve.92.030901] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2015] [Indexed: 06/05/2023]
Abstract
Two symmetrically coupled populations of N oscillators with inertia m display chaotic solutions with broken symmetry similar to experimental observations with mechanical pendulums. In particular, we report evidence of intermittent chaotic chimeras, where one population is synchronized and the other jumps erratically between laminar and turbulent phases. These states have finite lifetimes diverging as a power law with N and m. Lyapunov analyses reveal chaotic properties in quantitative agreement with theoretical predictions for globally coupled dissipative systems.
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Affiliation(s)
- Simona Olmi
- Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi, Via Madonna del Piano 10, I-50019 Sesto Fiorentino, Florence, Italy
- INFN Sezione Firenze, Via Sansone 1, I-50019 Sesto Fiorentino, Florence, Italy
| | - Erik A Martens
- Department of Biomedical Sciences, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen, Denmark
- Department of Mathematical Sciences, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
- Group of Biophysics and Evolutionary Dynamics, Max Planck Institute for Dynamics and Self-Organization, 37077 Göttingen, Lower Saxony, Germany
| | - Shashi Thutupalli
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
- Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - Alessandro Torcini
- Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi, Via Madonna del Piano 10, I-50019 Sesto Fiorentino, Florence, Italy
- INFN Sezione Firenze, Via Sansone 1, I-50019 Sesto Fiorentino, Florence, Italy
- Aix-Marseille Université, Inserm, INMED UMR 901 and Institut de Neurosciences des Systèmes UMR 1106, 13000 Marseille, France
- Aix-Marseille Université, Université de Toulon, CNRS, CPT, UMR 7332, 13288 Marseille, France
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14
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Thutupalli S, Sun M, Bunyak F, Palaniappan K, Shaevitz JW. Directional reversals enable Myxococcus xanthus cells to produce collective one-dimensional streams during fruiting-body formation. J R Soc Interface 2015; 12:20150049. [PMID: 26246416 PMCID: PMC4535398 DOI: 10.1098/rsif.2015.0049] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2015] [Accepted: 07/09/2015] [Indexed: 01/30/2023] Open
Abstract
The formation of a collectively moving group benefits individuals within a population in a variety of ways. The surface-dwelling bacterium Myxococcus xanthus forms dynamic collective groups both to feed on prey and to aggregate during times of starvation. The latter behaviour, termed fruiting-body formation, involves a complex, coordinated series of density changes that ultimately lead to three-dimensional aggregates comprising hundreds of thousands of cells and spores. How a loose, two-dimensional sheet of motile cells produces a fixed aggregate has remained a mystery as current models of aggregation are either inconsistent with experimental data or ultimately predict unstable structures that do not remain fixed in space. Here, we use high-resolution microscopy and computer vision software to spatio-temporally track the motion of thousands of individuals during the initial stages of fruiting-body formation. We find that cells undergo a phase transition from exploratory flocking, in which unstable cell groups move rapidly and coherently over long distances, to a reversal-mediated localization into one-dimensional growing streams that are inherently stable in space. These observations identify a new phase of active collective behaviour and answer a long-standing open question in Myxococcus development by describing how motile cell groups can remain statistically fixed in a spatial location.
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Affiliation(s)
- Shashi Thutupalli
- Joseph Henry Laboratories of Physics, Princeton University, Princeton, NJ 08544, USA Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, USA
| | - Mingzhai Sun
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
| | - Filiz Bunyak
- Department of Computer Science, University of Missouri, Columbia, MO 65211, USA
| | | | - Joshua W Shaevitz
- Joseph Henry Laboratories of Physics, Princeton University, Princeton, NJ 08544, USA Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
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15
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Abstract
Active emulsions, i.e., emulsions whose droplets perform self-propelled motion, are of tremendous interest for mimicking collective phenomena in biological populations such as phytoplankton and bacterial colonies, but also for experimentally studying rheology, pattern formation, and phase transitions in systems far from thermal equilibrium. For fuelling such systems, molecular processes involving the surfactants which stabilize the emulsions are a straightforward concept. We outline and compare two different types of reactions, one which chemically modifies the surfactant molecules, the other which transfers them into a different colloidal state. While in the first case symmetry breaking follows a standard linear instability, the second case turns out to be more complex. Depending on the dissolution pathway, there is either an intrinsically nonlinear instability, or no symmetry breaking at all (and hence no locomotion).
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Affiliation(s)
- Stephan Herminghaus
- Max-Planck Institute for Dynamics and Self-Organization, Göttingen, Germany.
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16
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Peddireddy K, Kumar P, Thutupalli S, Herminghaus S, Bahr C. Myelin structures formed by thermotropic smectic liquid crystals. Langmuir 2013; 29:15682-15688. [PMID: 24274621 DOI: 10.1021/la4038588] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We report on transient structures, formed by thermotropic smectic-A liquid crystals, resembling the myelin figures of lyotropic lamellar liquid crystals. The thermotropic myelin structures form during the solubilization of a smectic-A droplet in an aqueous phase containing a cationic surfactant at concentrations above the critical micelle concentration. Similar to the lyotropic myelin figures, the thermotropic myelins appear in an optical microscope as flexible tubelike structures growing at the smectic/aqueous interface. Polarizing microscopy and confocal fluorescence microscopy show that the smectic layers are parallel to the tube surface and form a cylindrically bent arrangement around a central line defect in the tube. We study the growth behavior of this new type of myelins and discuss similarities to and differences from the classical lyotropic myelin figures.
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Affiliation(s)
- Karthik Peddireddy
- Max Planck Institute for Dynamics and Self-Organization (MPIDS), 37077 Goettingen, Germany
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17
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Peddireddy K, Jampani VSR, Thutupalli S, Herminghaus S, Bahr C, Muševič I. Lasing and waveguiding in smectic A liquid crystal optical fibers. Opt Express 2013; 21:30233-30242. [PMID: 24514602 DOI: 10.1364/oe.21.030233] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We demonstrate a new class of soft matter optical fibers, which are self-assembled in a form of smectic-A liquid crystal microtubes grown in an aqueous surfactant dispersion of a smectic-A liquid crystal. The diameter of the fibers is highly uniform and the fibers are highly birefringent. They are characterized by a line topological defect in the core of the fiber with an optical axis pointing from the defect core towards the surface. We demonstrate guiding of light along the fiber and Whispering Gallery Mode (WGM) lasing in a plane perpendicular to the fiber. The light guiding as well as the lasing threshold are significantly dependent on the polarization of the excitation beam. The observed threshold for WGM lasing is very low (≈ 75μJ/cm(2)) when the pump beam polarization is perpendicular to the direction of the laser dye alignment and is similar to the lasing threshold in nematic droplets. The smectic-A fibers are soft and flexible and can be manipulated with laser tweezers demonstrating a promising approach for realization of soft photonic circuits.
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18
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Wartel M, Ducret A, Thutupalli S, Czerwinski F, Le Gall AV, Mauriello EMF, Bergam P, Brun YV, Shaevitz J, Mignot T. A versatile class of cell surface directional motors gives rise to gliding motility and sporulation in Myxococcus xanthus. PLoS Biol 2013; 11:e1001728. [PMID: 24339744 PMCID: PMC3858216 DOI: 10.1371/journal.pbio.1001728] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2013] [Accepted: 10/23/2013] [Indexed: 01/16/2023] Open
Abstract
The Myxococcus Agl-Nfs machinery, a type of bacterial transport system, is modular and is seen to also rotate a carbohydrate polymer directionally at the spore surface to assist spore coat assembly. Eukaryotic cells utilize an arsenal of processive transport systems to deliver macromolecules to specific subcellular sites. In prokaryotes, such transport mechanisms have only been shown to mediate gliding motility, a form of microbial surface translocation. Here, we show that the motility function of the Myxococcus xanthus Agl-Glt machinery results from the recent specialization of a versatile class of bacterial transporters. Specifically, we demonstrate that the Agl motility motor is modular and dissociates from the rest of the gliding machinery (the Glt complex) to bind the newly expressed Nfs complex, a close Glt paralogue, during sporulation. Following this association, the Agl system transports Nfs proteins directionally around the spore surface. Since the main spore coat polymer is secreted at discrete sites around the spore surface, its transport by Agl-Nfs ensures its distribution around the spore. Thus, the Agl-Glt/Nfs machineries may constitute a novel class of directional bacterial surface transporters that can be diversified to specific tasks depending on the cognate cargo and machinery-specific accessories. Many living cells use processive cytoskeletal motors to transport proteins and subcellular organelles to specific subcellular sites. In bacteria, this type of transport has yet to be identified and it is generally thought that random protein collisions underlie most biochemical processes. In recent years, our view of the bacterial cell was changed by the discovery of subcellular compartmentalization and a cytoskeleton, suggesting that processive motors might also operate in prokaryotes. We previously characterized a mechanism of intracellular transport that drives cell motility across solid surfaces in the gram-negative bacterium Myxococcus xanthus. Since the transport apparatus was also found in bacterial species that do not move on surfaces, we postulated that intracellular transport underlies other cellular processes in bacteria. Indeed, we show here that the Myxococcus motility motor can be adapted to transport sporulation-specific proteins around the nascent spore surface. Because the transported proteins are linked to the main spore coat, this motion assists the assembly of a protective spore coat. In conclusion, the Myxococcus motility/sporulation transport machinery defines an emerging class of versatile transport systems, suggesting that processive transport has been overlooked and may well orchestrate many processes in bacteria.
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Affiliation(s)
- Morgane Wartel
- Laboratoire de Chimie Bactérienne, CNRS UMR 7283, Aix-Marseille Université, Institut de Microbiologie de la Méditerranée, Marseille, France
| | - Adrien Ducret
- Laboratoire de Chimie Bactérienne, CNRS UMR 7283, Aix-Marseille Université, Institut de Microbiologie de la Méditerranée, Marseille, France
- Department of Biology, Indiana University, Bloomington, Indiana, United States of America
| | - Shashi Thutupalli
- Department of Physics and the Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey, United States of America
| | - Fabian Czerwinski
- Department of Physics and the Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey, United States of America
| | - Anne-Valérie Le Gall
- Laboratoire de Chimie Bactérienne, CNRS UMR 7283, Aix-Marseille Université, Institut de Microbiologie de la Méditerranée, Marseille, France
| | - Emilia M. F. Mauriello
- Laboratoire de Chimie Bactérienne, CNRS UMR 7283, Aix-Marseille Université, Institut de Microbiologie de la Méditerranée, Marseille, France
| | - Ptissam Bergam
- Plateforme de Microscopie, Institut de Microbiologie de la Méditerranée, Marseille, France
| | - Yves V. Brun
- Department of Biology, Indiana University, Bloomington, Indiana, United States of America
| | - Joshua Shaevitz
- Department of Physics and the Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey, United States of America
| | - Tâm Mignot
- Laboratoire de Chimie Bactérienne, CNRS UMR 7283, Aix-Marseille Université, Institut de Microbiologie de la Méditerranée, Marseille, France
- * E-mail:
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19
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Thutupalli S, Herminghaus S. Tuning active emulsion dynamics via surfactants and topology. Eur Phys J E Soft Matter 2013; 36:91. [PMID: 23989755 DOI: 10.1140/epje/i2013-13091-2] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2012] [Revised: 01/23/2013] [Accepted: 07/12/2013] [Indexed: 06/02/2023]
Abstract
We study water-in-oil emulsion droplets, running the Belousov-Zhabotinsky reaction, that form a new type of synthetic active matter unit. These droplets, stabilised by surfactants dispersed in the oil medium, are capable of internal chemical oscillations and self-propulsion. Here we present studies of networks of such self-propelled chemical oscillators and show that the resulting dynamics depend strongly on the topology of the active matter units and their connections. The chemical oscillations can couple via the exchange of promoter and inhibitor type of reaction intermediates across the droplets under precise conditions of surfactant bilayer formation between the droplets. The self-emerging synchronization dynamics are then characterized by the topology of the oscillator networks. Further, we show that the chemical oscillations inside the droplets cause oscillatory speed variations in the motion of individual droplets, extending our previous studies on such swimmers. Finally, we demonstrate that qualitatively new types of self-propelled motion can occur when simple droplet networks, for example two droplets connected by a bilayer, are set into motion. Altogether, these results lead to exciting possibilities in future studies of autonomous active matter.
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Affiliation(s)
- Shashi Thutupalli
- Max Planck Institute for Dynamics and Self-organization, Göttingen, Germany.
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20
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Thutupalli S, Fleury JB, Steinberger A, Herminghaus S, Seemann R. Why can artificial membranes be fabricated so rapidly in microfluidics? Chem Commun (Camb) 2013; 49:1443-5. [PMID: 23321691 DOI: 10.1039/c2cc38867g] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Droplet interface bilayers are a convenient tool to produce and explore lipid membrane properties. We discuss why their formation time in microfluidics can be three to six orders of magnitude faster compared to conventional bulk settings.
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21
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Peddireddy K, Kumar P, Thutupalli S, Herminghaus S, Bahr C. Solubilization of thermotropic liquid crystal compounds in aqueous surfactant solutions. Langmuir 2012; 28:12426-31. [PMID: 22799600 DOI: 10.1021/la3015817] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We study the micellar solubilization of three thermotropic liquid crystal compounds by immersing single drops in aqueous solutions of the ionic surfactant tetradecyltrimethylammonium bromide. For both nematic and isotropic drops, we observe a linear decrease of the drop size with time as well as convective flows and self-propelled motions. The solubilization is accompanied by the appearance of small aqueous droplets within the nematic or isotropic drop. At low temperatures, nematic drops expell small nematic droplets into the aqueous environment. Smectic drops show the spontaneous formation of filament-like structures which resemble the myelin figures observed in lyotropic lamellar systems. In all cases, the liquid crystal drops become completely solubilized, provided the weight fraction of the liquid crystal in the system is not larger than a few percent. The solubilization of the liquid crystal drops is compared with earlier studies of the solubilization of alkanes in ionic surfactant solutions.
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Affiliation(s)
- Karthik Peddireddy
- Max Planck Institute for Dynamics and Self-Organization (MPIDS), 37077 Goettingen, Germany
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22
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van den Bogaart G, Thutupalli S, Risselada JH, Meyenberg K, Holt M, Riedel D, Diederichsen U, Herminghaus S, Grubmüller H, Jahn R. Synaptotagmin-1 may be a distance regulator acting upstream of SNARE nucleation. Nat Struct Mol Biol 2011; 18:805-12. [PMID: 21642968 PMCID: PMC3130798 DOI: 10.1038/nsmb.2061] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2010] [Accepted: 03/17/2011] [Indexed: 12/16/2022]
Abstract
Synaptotagmin-1 triggers Ca2+-sensitive, rapid neurotransmitter release by promoting the interaction of SNARE proteins between the synaptic vesicles and the plasma membrane. How synaptotagmin-1 promotes this interaction is controversial, and the massive increase in membrane fusion efficiency of Ca2+-synaptotagmin-1 has not been reproduced in vitro. However, previous experiments have been performed at relatively high salt concentrations, screening potentially important electrostatic interactions. Using functional reconstitution in liposomes, we show here that at low ionic strength SNARE-mediated membrane fusion becomes strictly dependent on both Ca2+ and synaptotagmin-1. Under these conditions, synaptotagmin-1 functions as a distance regulator: tethering the liposomes too far for SNARE nucleation in the absence of Ca2+, but brings the liposomes close enough for membrane fusion in the presence of Ca2+. These results may explain how the relatively weak electrostatic interactions of synaptotagmin-1 with membranes substantially accelerate fusion.
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Affiliation(s)
- Geert van den Bogaart
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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