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Smokers IB, Visser BS, Slootbeek AD, Huck WTS, Spruijt E. How Droplets Can Accelerate Reactions─Coacervate Protocells as Catalytic Microcompartments. Acc Chem Res 2024; 57:1885-1895. [PMID: 38968602 PMCID: PMC11256357 DOI: 10.1021/acs.accounts.4c00114] [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: 02/22/2024] [Revised: 04/24/2024] [Accepted: 06/03/2024] [Indexed: 07/07/2024]
Abstract
ConspectusCoacervates are droplets formed by liquid-liquid phase separation (LLPS) and are often used as model protocells-primitive cell-like compartments that could have aided the emergence of life. Their continued presence as membraneless organelles in modern cells gives further credit to their relevance. The local physicochemical environment inside coacervates is distinctly different from the surrounding dilute solution and offers an interesting microenvironment for prebiotic reactions. Coacervates can selectively take up reactants and enhance their effective concentration, stabilize products, destabilize reactants and lower transition states, and can therefore play a similar role as micellar catalysts in providing rate enhancement and selectivity in reaction outcome. Rate enhancement and selectivity must have been essential for the origins of life by enabling chemical reactions to occur at appreciable rates and overcoming competition from hydrolysis.In this Accounts, we dissect the mechanisms by which coacervate protocells can accelerate reactions and provide selectivity. These mechanisms can similarly be exploited by membraneless organelles to control cellular processes. First, coacervates can affect the local concentration of reactants and accelerate reactions by copartitioning of reactants or exclusion of a product or inhibitor. Second, the local environment inside the coacervate can change the energy landscape for reactions taking place inside the droplets. The coacervate is more apolar than the surrounding solution and often rich in charged moieties, which can affect the stability of reactants, transition states and products. The crowded nature of the droplets can favor complexation of large molecules such as ribozymes. Their locally different proton and water activity can facilitate reactions involving a (de)protonation step, condensation reactions and reactions that are sensitive to hydrolysis. Not only the coacervate core, but also the surface can accelerate reactions and provides an interesting site for chemical reactions with gradients in pH, water activity and charge. The coacervate is often rich in catalytic amino acids and can localize catalysts like divalent metal ions, leading to further rate enhancement inside the droplets. Lastly, these coacervate properties can favor certain reaction pathways, and thereby give selectivity over the reaction outcome.These mechanisms are further illustrated with a case study on ribozyme reactions inside coacervates, for which there is a fine balance between concentration and reactivity that can be tuned by the coacervate composition. Furthermore, coacervates can both catalyze ribozyme reactions and provide product selectivity, demonstrating that coacervates could have functioned as enzyme-like catalytic microcompartments at the origins of life.
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Affiliation(s)
- Iris B.
A. Smokers
- Institute for Molecules and
Materials, Radboud University, Heyendaalseweg 135, 6523 AJ Nijmegen, The Netherlands
| | - Brent S. Visser
- Institute for Molecules and
Materials, Radboud University, Heyendaalseweg 135, 6523 AJ Nijmegen, The Netherlands
| | - Annemiek D. Slootbeek
- Institute for Molecules and
Materials, Radboud University, Heyendaalseweg 135, 6523 AJ Nijmegen, The Netherlands
| | - Wilhelm T. S. Huck
- Institute for Molecules and
Materials, Radboud University, Heyendaalseweg 135, 6523 AJ Nijmegen, The Netherlands
| | - Evan Spruijt
- Institute for Molecules and
Materials, Radboud University, Heyendaalseweg 135, 6523 AJ Nijmegen, The Netherlands
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Landfield H, Kalamaris N, Wang M. Extreme dependence of dynamics on concentration in highly crowded polyelectrolyte solutions. SCIENCE ADVANCES 2024; 10:eado4976. [PMID: 38959308 PMCID: PMC11221520 DOI: 10.1126/sciadv.ado4976] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2024] [Accepted: 05/30/2024] [Indexed: 07/05/2024]
Abstract
Charge-carrying species, such as polyelectrolytes, are vital to natural and synthetic processes that rely on their dynamic behavior. Through single-particle tracking techniques, the diffusivity of individual polyelectrolyte chains and overall system viscosity are determined for concentrated polylysine solutions. These studies show scaling dependences of D ~ c-6.1 and η ~ c7.2, much stronger than theoretical predictions, drawing the applicability of power law fits into question. Similar trends are observed in concentrated solutions prepared at various pH and counterion conditions. These hindered system dynamics appear universal to polyelectrolyte systems and are attributed to the large effective excluded volumes of polyelectrolyte chains inducing glassy dynamics. The framework of the Vrentas-Duda free-volume theory is used to compare polyelectrolyte and neutral systems. Supported by this theory, excluding counterion mass from total polymer mass results in all environmental conditions collapsing onto a common trendline. These results are applicable to crowded biological systems, such as intracellular environments where protein mobility is strongly inhibited.
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Affiliation(s)
- Harrison Landfield
- Department of Chemical and Biological Engineering, Northwestern University, Evanston, IL 60208, USA
| | - Nicholas Kalamaris
- Department of Chemical and Biological Engineering, Northwestern University, Evanston, IL 60208, USA
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Holkar A, Gao S, Villaseñor K, Lake M, Srivastava S. Quantitative turbidimetric characterization of stabilized complex coacervate dispersions. SOFT MATTER 2024; 20:5060-5070. [PMID: 38743276 DOI: 10.1039/d3sm01761c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2024]
Abstract
Stabilizing complex coacervate microdroplets is desirable due to their various applications, such as bioreactors, drug delivery vehicles, and encapsulants. Here, we present quantitative characterization of complex coacervate dispersion stability inferred by turbidimetry measurements. The stability of the dispersions is shown to be modulated by the concentrations of comb polyelectrolyte (cPE) stabilizers and salt. We demonstrate cPEs as effective stabilizers for complex coacervate dispersions independent of the chemistry or length of the constituent polyelectrolytes, salts, or preparation routes. By monitoring the temporal evolution of dispersion turbidity, we show that cPEs suppress microdroplet coalescence with minimal change in microdroplet sizes over 48 hours, even at salt concentrations up to 300 mM. The number density and average microdroplet size are shown to be controlled by varying the cPE and salt concentrations. Lastly, turbidity maps, akin to binodal phase maps, depict an expansion of the turbid two-phase region and an increase in the salt resistance of the coacervates upon the introduction of cPEs. The coacervate salt resistance is shown to increase by >3×, and this increase is maintained for up to 15 days, demonstrating that cPEs impart higher salt resistance over extended durations.
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Affiliation(s)
- Advait Holkar
- Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, CA 90095, USA.
| | - Shang Gao
- Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, CA 90095, USA.
| | - Kathleen Villaseñor
- Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, CA 90095, USA.
| | - Michael Lake
- NSF BioPACIFIC MIP, University of California, Los Angeles, Los Angeles, CA 90095, USA
- California NanoSystems Institute, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Samanvaya Srivastava
- Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, CA 90095, USA.
- NSF BioPACIFIC MIP, University of California, Los Angeles, Los Angeles, CA 90095, USA
- California NanoSystems Institute, University of California, Los Angeles, Los Angeles, CA 90095, USA
- Institute for Carbon Management, University of California, Los Angeles, Los Angeles, CA 90095, USA
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Wilcox K, Yamagami KR, Roopnarine BK, Linscott A, Morozova S. Effect of Polymer Gel Elasticity on Complex Coacervate Phase Behavior. ACS POLYMERS AU 2024; 4:109-119. [PMID: 38618006 PMCID: PMC11010254 DOI: 10.1021/acspolymersau.3c00027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Revised: 12/07/2023] [Accepted: 12/11/2023] [Indexed: 04/16/2024]
Abstract
Gels are key materials in biological systems such as tissues and may control biocondensate formation and structure. To further understand the effects of elastic environments on biomacromolecular assembly, we have investigated the phase behavior and radii of complex coacervate droplets in polyacrylamide (PAM) networks as a function of gel modulus. Poly-l-lysine (PLL) and sodium hyaluronate (HA) complex coacervate phases were prepared in PAM gels with moduli varying from 0.035 to 15.0 kPa. The size of the complex coacervate droplets is reported from bright-field microscopy and confocal fluorescence microscopy. Overall, the complex coacervate droplet volume decreases inversely with the modulus. Fluorescence microscopy is also used to determine the phase behavior and concentration of fluorescently tagged HA in the complex coacervate phases as a function of ionic strength (100-270 mM). We find that the critical ionic strength and complex coacervate stability are nonmonotonic as a function of the network modulus and that the local gel concentration can be used to control phase behavior and complex coacervate droplet size scale. By understanding how elastic environments influence simple electrostatic assembly, we can further understand how biomacromolecules exist in complex, crowded, and elastic cellular environments.
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Affiliation(s)
- Kathryn
G. Wilcox
- Department of Macromolecular
Science and Engineering, Case Western Reserve
University, Cleveland, Ohio 44106, United States
| | - Kai R. Yamagami
- Department of Macromolecular
Science and Engineering, Case Western Reserve
University, Cleveland, Ohio 44106, United States
| | - Brittany K. Roopnarine
- Department of Macromolecular
Science and Engineering, Case Western Reserve
University, Cleveland, Ohio 44106, United States
| | - Adam Linscott
- Department of Macromolecular
Science and Engineering, Case Western Reserve
University, Cleveland, Ohio 44106, United States
| | - Svetlana Morozova
- Department of Macromolecular
Science and Engineering, Case Western Reserve
University, Cleveland, Ohio 44106, United States
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Staňo R, van Lente J, Lindhoud S, Košovan P. Sequestration of Small Ions and Weak Acids and Bases by a Polyelectrolyte Complex Studied by Simulation and Experiment. Macromolecules 2024; 57:1383-1398. [PMID: 38370910 PMCID: PMC10867894 DOI: 10.1021/acs.macromol.3c01209] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2023] [Revised: 11/27/2023] [Accepted: 11/29/2023] [Indexed: 02/20/2024]
Abstract
Mixing of oppositely charged polyelectrolytes can result in phase separation into a polymer-poor supernatant and a polymer-rich polyelectrolyte complex (PEC). We present a new coarse-grained model for the Grand-reaction method that enables us to determine the composition of the coexisting phases in a broad range of pH and salt concentrations. We validate the model by comparing it to recent simulations and experimental studies, as well as our own experiments on poly(acrylic acid)/poly(allylamine hydrochloride) complexes. The simulations using our model predict that monovalent ions partition approximately equally between both phases, whereas divalent ones accumulate in the PEC phase. On a semiquantitative level, these results agree with our own experiments, as well as with other experiments and simulations in the literature. In the sequel, we use the model to study the partitioning of a weak diprotic acid at various pH values of the supernatant. Our results show that the ionization of the acid is enhanced in the PEC phase, resulting in its preferential accumulation in this phase, which monotonically increases with the pH. Currently, this effect is still waiting to be confirmed experimentally. We explore how the model parameters (particle size, charge density, permittivity, and solvent quality) affect the measured partition coefficients, showing that fine-tuning of these parameters can make the agreement with the experiments almost quantitative. Nevertheless, our results show that charge regulation in multivalent solutes can potentially be exploited in engineering the partitioning of charged molecules in PEC-based systems at various pH values.
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Affiliation(s)
- Roman Staňo
- Faculty
of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna, Austria
- Vienna
Doctoral School in Physics, University of
Vienna, Boltzmanngasse
5, 1090 Vienna, Austria
| | - Jéré
J. van Lente
- Department
of Molecules & Materials, University
of Twente, Drienerlolaan 5, 7522 NB Enschede, The Netherlands
| | - Saskia Lindhoud
- Department
of Molecules & Materials, University
of Twente, Drienerlolaan 5, 7522 NB Enschede, The Netherlands
| | - Peter Košovan
- Department
of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, 128 40 Prague 2, Czech Republic
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Chen S, Wang ZG. Driving force and pathway in polyelectrolyte complex coacervation. Proc Natl Acad Sci U S A 2022; 119:e2209975119. [PMID: 36037377 PMCID: PMC9457374 DOI: 10.1073/pnas.2209975119] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Accepted: 08/01/2022] [Indexed: 11/18/2022] Open
Abstract
There is notable discrepancy between experiments and coarse-grained model studies regarding the thermodynamic driving force in polyelectrolyte complex coacervation: experiments find the free energy change to be dominated by entropy, while simulations using coarse-grained models with implicit solvent usually report a large, even dominant energetic contribution in systems with weak to intermediate electrostatic strength. Here, using coarse-grained, implicit-solvent molecular dynamics simulation combined with thermodynamic analysis, we study the potential of mean force (PMF) in the two key stages on the coacervation pathway for symmetric polyelectrolyte mixtures: polycation-polyanion complexation and polyion pair-pair condensation. We show that the temperature dependence in the dielectric constant of water gives rise to a substantial entropic contribution in the electrostatic interaction. By accounting for this electrostatic entropy, which is due to solvent reorganization, we find that under common conditions (monovalent ions, room temperature) for aqueous systems, both stages are strongly entropy-driven with negligible or even unfavorable energetic contributions, consistent with experimental results. Furthermore, for weak to intermediate electrostatic strengths, this electrostatic entropy, rather than the counterion-release entropy, is the primary entropy contribution. From the calculated PMF, we find that the supernatant phase consists predominantly of polyion pairs with vanishingly small concentration of bare polyelectrolytes, and we provide an estimate of the spinodal of the supernatant phase. Finally, we show that prior to contact, two neutral polyion pairs weakly attract each other by mutually induced polarization, providing the initial driving force for the fusion of the pairs.
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Affiliation(s)
- Shensheng Chen
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125
| | - Zhen-Gang Wang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125
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