Designing Electrostatic Interactions via Polyelectrolyte Monomer Sequence

Abstract

Charged polymers are ubiquitous in biological systems because electrostatic interactions can drive complicated structure formation and respond to environmental parameters such as ionic strength and pH. In these systems, function emerges from sophisticated molecular design; for example, intrinsically disordered proteins leverage specific sequences of monomeric charges to control the formation and function of intracellular compartments known as membraneless organelles. The role of a charged monomer sequence in dictating the strength of electrostatic interactions remains poorly understood despite extensive evidence that sequence is a powerful tool biology uses to tune soft materials. In this article, we use a combination of theory, experiment, and simulation to establish the physical principles governing sequence-driven control of electrostatic interactions. We predict how arbitrary sequences of charge give rise to drastic changes in electrostatic interactions and correspondingly phase behavior. We generalize a transfer matrix formalism that describes a phase separation phenomenon known as “complex coacervation” and provide a theoretical framework to predict the phase behavior of charge sequences. This work thus provides insights into both how charge sequence is used in biology and how it could be used to engineer properties of synthetic polymer systems.

Temperature, Hydrostatic Pressure, and Osmolyte Effects on Liquid–Liquid Phase Separation in Protein Condensates: Physical Chemistry and Biological Implications

“…Knowledge of the LLPS behavior of proteins as af unction of all thermodynamic variables, including pressure, is of directr elevance to recent efforts to designp roteinlike heteropolymer sequences with novel materials properties, including desirableL LPS behaviors. [36,[65][66][67][68][69][70]169] In ab roader technological context,s uch knowledge is also essential in areass uch as protein crystallization (LLPS occurs generally under conditions where the protein is metastablew ith respectt oc rystallization), protein purification, formulation development for therapeutic proteins (including the possibility of operating at industrial scales larger than other relatedt echniques as ultrafiltration, drying,c hromatography,a nd dialysis), and high-pressuref ood processing. [2,3,49,73,74,[196][197][198] It is hoped that the present summary of the initial yetpromising findings on pressure effects on biomolecular condensates will spur more efforts in this exciting area of interdisciplinary research.…”

“…novel materials properties. [36,[65][66][67][68][69][70] Knowledge of the phase behavior of proteins is also essential in areas such as protein purificationa nd long-term storagea sw ella sf or high-pressure food processing. [2,45,49,[71][72][73][74] Taking ab asic step in our endeavor to better understand biomolecular LLPS, our focus here is on the equilibrium thermodynamics for the fundamental physical insights it offers, withoutl osing sight of the fact that biologically functional condensates are, in many respects, highly complex "active liquids" [40,75] regulated by chemical reactions, posttranslational modifications, and other non-equilibrium processes.…”

Patterning Polyelectrolyte Complexes with Alternating Monomer Sequence Distributions

“…Nuclear magnetic resonance (NMR) spectra were acquired on a Bruker AVANCE III HD NMR spectrometer operating at a proton frequency of 600.13 MHz and utilizing a 5mm inverse triple resonance gradient probe tuned to 1 H, 13 C, and 15 N. All samples were dissolved in 0.5 mL D2O and spectra were acquired at 30˚C. A series of 1 H 1D, NOESY, TOCSY, and 1 H, 13 C HSQC spectra were acquired. Typical 1 H 90˚ times were 9.8 µs and the recycle delay was 1 s. In the 1 H 1D spectra, 8 k complex points were acquired over a spectral width of 15 ppm with a resulting acquisition time of 0.91s.…”

“…Typical 1 H 90˚ times were 9.8 µs and the recycle delay was 1 s. In the 1 H 1D spectra, 8 k complex points were acquired over a spectral width of 15 ppm with a resulting acquisition time of 0.91s. In the 2D spectra, 1k complex points were typically taken over 11 ppm in the directly detected dimension (acquisition time 160 ms), while in the indirectly detected dimension 128 complex points were acquired with a 11 ppm spectral width for 1 H in the NOESY, and TOCSY spectra and 140 ppm for the 13 C spectral width in 1 H, 13 C HSQC. Selective TOCSY and NOESY spectra were used to probe the through bond and through space proximity of specific 1 H nuclei.…”

Hydropathy patterning complements charge patterning to describe conformational preferences of disordered proteins

“…Significant previous work has already highlighted the role of sequence charge patterning on the properties of IDPs and important order parameters, such as sequence charge decoration (SCD) and κ, are available to describe such effects. [42][43][44]55,56 Given the success of such strategies, we focus on developing a descriptor for the patterning of uncharged residues. Here we start with an amino-acid specific hydropathy value (λ), 57 normalized to a value between 0 and 1, as the relevant feature to describe or predict a protein's compactness, and equivalently the polymer scaling properties.…”