Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session S35: Electrostatic Complexation of Proteins and Protein MimicsFocus
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Sponsoring Units: DPOLY Chair: Samanvaya Srivastava, University of California, Los Angeles Room: 507 |
Thursday, March 5, 2020 11:15AM - 11:27AM |
S35.00001: The Effect of Protein Surface Charge Distribution on Protein-Polymer Complexation Sieun Kim, Hursh Sureka, Basak Kayitmazer, Bradley Olsen Charge patches on protein surfaces have been known to play a significant role in the coacervation and complexation of proteins with one another and with polymers; however, quantifying this patchiness has remained elusive. We present a methodology for quantifying the charge patchiness of protein surfaces and measure how the patchiness of a panel of proteins—engineered to have the same charge, but different charge distributions—affects complexation with a variety of polyelectrolytes. The panel complexed most strongly with the strong polycation used, poly(1-methyl-4-vinylpyridinium iodide), with the proteins with the largest patches complexing over a broader range of polymer-protein ratios than those with smaller patches. Only weaker complexation was seen with the other polyelectrolytes screened, which may have been driven by the weak net negative charge of the mutants. However, the mutant with the largest patches was found to form soluble complexes with both of the weak polyanions tested, hyaluronic acid and poly(acrylic acid). A cutoff between 0.25 and 0.3 in the patchiness parameter was predictive for whether the mutants would complex with any of the polymers tested (particularly qP4VP). |
Thursday, March 5, 2020 11:27AM - 11:39AM |
S35.00002: Influence of charge heterogeneity and charge regulation in complexation between proteins and weak polyelectrolytes. Rituparna Samanta, Venkatraghavan Ganesan We discuss the complexation of weakly dissociating proteins in the presence of oppositely charged polyelectrolytes using coarse-grained molecular simulations. We have used singe chain in mean field simulation method with constant pH ensemble in a semi-grand canonical framework to include the charge dissociation effects. Through results (adsorption and bridging) pertaining to one and two proteins and several polyelectrolytes, we compare the influence of charge regulation and charge heterogeneities on proteins. Our results demonstrate that the charge regulation exerts bridging by polymers higher than that due to charge patches. We discuss the influence of different parameters such as polyelectrolyte concentration, number of charge patches, pH etc. |
Thursday, March 5, 2020 11:39AM - 11:51AM |
S35.00003: Coacervate gel composites: Phase behavior and topologically frustrated dynamical hierarchy Di Jia, Murugappan Muthukumar We report the discovery of a novel coacervate gel composite state and experimental results on the phase behavior and dynamics of this state. This state is qualitatively different from the traditional coacervate liquid states composed of oppositely charged macromolecules formed via liquid-liquid phase separation. The cross-linking of one of the components of our system induces a new dynamical state for the oppositely charged guest polymer. In this state, the guest molecule is topologically frustrated exhibiting a hierarchy of internal chain dynamics, and is non-diffusive, although the water content in the coacervate gel is very high. In addition, we find rich phase behaviors as a function of cross-linking of one component, charge stoichiometry, pH, and salt concentration. An interlude of an coacervate-emulsion phase prior to the gel formation and its response to cross-linking at different experimental control variables will be presented. |
Thursday, March 5, 2020 11:51AM - 12:03PM |
S35.00004: SAXS Investigations of Structure and Phase Behavior of Polyelectrolyte–Nanoparticle Assemblies Advait Holkar, Jesse Toledo, Samanvaya Srivastava Aqueuous mixtures of oppositely charged polyelectrolytes (PE) and nanoparticles (NP) self-assemble into dense complexes. This self-assembly forms the basis of diverse phenomena ranging from flocculant action in water treatment, where the PE-NP flocs phase separate and sediment, to DNA compaction around histone proteins into chromatin. Factors such as the PE length, architecture and concentrations; NP charge, morphology and concentrations; and solution conditions (pH and ionic strength) play key roles in directing these PE-NP assemblies. In this presentation, we will delineate fundamental investigations into the phase behavior and structure of polycation-silica NP assemblies using small angle X-ray scattering, turbidimetry and thermogravimetric analysis with systematic variation of PE sizes and flexibility, NP sizes, and a wide range of concentrations of both components. Trends in interparticle spacings and correlations as well as fractal dimensions of assemblies with varying PE and NP concentrations will be discussed, presenting a comprehensive narrative of the hierarchical structure of PE-NP self-assemblies. Near-contact compaction of NPs in the PE-NP assemblies above a critical ratio of PE and NP concentrations will be highlighted. |
Thursday, March 5, 2020 12:03PM - 12:15PM |
S35.00005: Stabilizing Membraneless Polyelectrolyte Complex Coacervates Towards Inherent Coalescence Aman Agrawal, Alamgir Karim Although recent interests in polyelectrolyte coacervates have shown their advanced applications such as microscale bioreactors with enhanced transcription rates, these applications are, however, usually limited to spatially isolated coacervate droplets or those with lipid or polymer membrane because of membraneless droplets’ instability towards coalescence. In this experimental work, we systematically explored the role of the droplet size distribution (~1-10 μm), negative to positive monomer ratio, and salt concentrations in governing the zeta potential and the long-term stability of droplets. We worked with a well-studied coacervate system: PDDA - ATP. Near-uniform size droplets were formed using a PDMS based microfluidic flow-focusing system in the laminar flow (Re<2100). As has been shown earlier, droplets with narrow size distribution had higher stability and coalesced slowly, over a period of several days, as compared to polydisperse droplets which were stable only for minutes to hours before coalescing. This work has an important consequence as this analysis allows us to understand the stability of various phase-separated liquid systems formed in vivo which finds applications ranging from protein storage to neurodegenerative diseases. |
Thursday, March 5, 2020 12:15PM - 12:27PM |
S35.00006: Protein Purification by Complex Coacervation Rachel Kapelner, Allie Obermeyer Proteins are an important class of biomolecules with applications across many industries, including as therapeutics and biocatalysts. Their use in some industries, such as the food and pharmaceutical industries, require a high degree of protein purity for their products. Therefore, a highly selective, yet high throughput and low-cost purification method is of great interest to purify proteins from cell lysate. Complex coacervation, the liquid-liquid phase separation of oppositely charged polyelectrolytes, shows promise as a protein purification technique. Previous work in the field, however, has only addressed separating a protein of interest from a relatively simple mixture. In this work, we demonstrate the utility of complex coacervation as a platform to purify proteins from cell lysate. Using a spectroscopic method, we designed a high throughput approach to screen protein purity and recovery from cell lysate. We were then able to assess how protein and polymer design properties and solution conditions impact protein purity and recovery from cell lysate. |
Thursday, March 5, 2020 12:27PM - 12:39PM |
S35.00007: Effects of therapeutic chemical modifications on polyelectrolyte properties of oligonucleotides Jeffrey Vieregg, Alexander E. Marras, Matthew Tirrell Polyelectrolyte complex micelles (PCMs), core-shell nanoparticles formed by complexation of polyelectrolytes and polyelectrolyte - hydrophilic neutral block copolymers, are an interesting laboratory for studying polyelectrolyte physics. They also provide an attractive solution to the longstanding problem of delivering therapeutic nucleic acids into cells, as nucleic acids are highly charged anions and are efficiently complexed by cationic polyelectrolytes. We recently published a set of structure-property data that provides rules for constructing DNA oligonucleotide PCMs with well-controlled morphology and low polydispersity and have found that they are applicable to several other polyelectrolytes, suggesting the possibility of developing general principles for PCM self-assembly. DNA oligonucleotides are accessible and chemically stable but are not bioactive, motivating investigation of how chemical modifications affect oligonucleotides’ polyelectrolyte properties. Surprisingly, we find that even single atom changes (e.g. DNA to RNA, or phosphate to phosphorothioate) can have large effects on the properties of the resulting PCMs. I will discuss these, and their interpretation, which highlight the need to include chemical information in models of polyelectrolyte complexation. |
Thursday, March 5, 2020 12:39PM - 12:51PM |
S35.00008: From Monomer Sequence to Self-Assembly in Polyelectrolyte Coacervation Gary Min Chiang Ong, Tyler Lytle, Charles Sing Oppositely-charged polyelectrolytes can undergo an associative phase separation known as complex coacervation, forming dense polymer phases that maximize favorable electrostatic interactions. This interaction motif can be harnessed to drive polymer assembly, via the incorporation of opposite charges on pairs of block copolymers. We present a recent theory developed to describe the equilibrium phase behavior of complex coacervation, capable of predicting both the correlated molecular structure of the bulk coacervate phase as well as matching experimental phase diagrams. We incorporate this model into a self-consistent field theory (SCFT) of polyelectrolyte self-assembly to predict phase diagrams, revealing a correspondence between salt concentration in charge-driven assembly and temperature in solvophobicity-driven assembly. We also show the limits of blockiness, mapping out the transition between micro-phase separated and macro-phase separated polymers as a function of the monomer sequence on a polyelectrolyte. |
Thursday, March 5, 2020 12:51PM - 1:03PM |
S35.00009: Sequence-Controlled Complex Coacervation of Random Polyelectrolytes Artem Rumyantsev, Nicholas Jackson, Boyuan Yu, Jeffrey M Ting, Wei Chen, Matthew Tirrell, Juan De Pablo The primary sequence of monomers along a backbone of heteropolymers impacts their physical properties. Random heteropolymers with the sequences following a first-order Markov process arise from statistical copolymerization of different monomers. In this work, we study complex coacervation of oppositely charged, random polyelectrolytes, i.e., polyanions and polycations containing statistically distributed charged and uncharged units. It is shown that increasing blockiness of charged monomers in the primary structure of the random polyelectrolytes favors the formation of dense coacervates. Charge blockiness also improves coacervate salt resistance and increases the width of the two-phase solution region. This effect is due to the enhanced cooperativity of Coulomb interactions between oppositely charged monomers within the coacervate. Our findings demonstrate that the solution phase behavior can be controlled through the design of the Markov monomer sequences, which are governed by the kinetics of statistical copolymerization. |
Thursday, March 5, 2020 1:03PM - 1:39PM |
S35.00010: Concentration and separation of proteins using polyion condensates Invited Speaker: Saskia Lindhoud When oppositely charged macromolecules are mixed in aqueous systems at the right conditions, i.e., ionic strength, mixing ratio, pH, etc., solutions phase separate in a condensed phase which is rich in macromolecules and a dilute phase. The so formed polyion condensate can be liquid-like or solid-like. In both cases proteins can be captured in the condensate phase. This protein partitioning strongly depends on the ratio between the oppositely charged macroions. |
Thursday, March 5, 2020 1:39PM - 1:51PM |
S35.00011: Complex coacervation of polymerized ionic liquids in non-aqueous solvents Minjung Lee, Ryan Hayward The formation of polyelectrolyte complex coacervates within solutions of two oppositely charged polymers is a topic of great recent interest. Studies to date have focused almost exclusively on polyelectrolyte mixtures in water or aqueous solvent mixtures. In this study, polymerized ionic liquids (PILs) were used to investigate the effects of solvent on complex coacervation in non-aqueous solvents. We constructed phase diagrams of PIL mixtures in non-aqueous solvents via experiments using UV-Vis and quantitative 19F-NMR spectroscopy, and found a substantial difference between two solvent systems in terms of the salt resistance, i.e., the concentration of added salt where complex coacervates are destroyed. Through these studies we seek to provide insight into the role of dielectric constant and solvent/polymer interactions on complex coacervation. |
Thursday, March 5, 2020 1:51PM - 2:03PM |
S35.00012: Computational Investigation of Sequence-Controlled Complex Coacervation in Statistical Copolymers Boyuan Yu, Nicholas Jackson, Artem Rumyantsev, Juan De Pablo Control of the monomer sequence of polymeric materials provides a pathway for the design of materials that mimic biomacromolecular complexity. In practice, this control can be achieved by tuning the reaction kinetics of random polymerization of different monomers, where the primary sequence distribution follows a first-order Markov chain. In this work, classical Gibbs ensemble and molecular dynamics simulations are used to explore the phase diagrams of polyelectrolyte coacervates with distinct monomer sequences controlled by a simple model for statistical copolymerization. Our results are summarized in phase diagrams that are in line with our previous theoretical findings and experimental observations including the fact that high charge “blockiness” within the sequence results in denser coacervates. Simulations also explore the important role of salt ion specificity as manifested by excluded volume interactions, and how these effects influence complex coacervate thermodynamics. The results presented in this work provide a deeper understanding of how chemical sequence can be used to control complex coacervation. |
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