Effect of salt additives on protein partition in polyethylene glycol–sodium sulfate aqueous two-phase systems

Mechanism of Phase Separation in Aqueous Two-Phase Systems

Liquid-liquid phase separation underlies the formation of membrane-less organelles inside living cells. The mechanism of this process can be examined using simple aqueous mixtures of two or more solutes, which are able to phase separate at specific concentration thresholds. This work presents the first experimental evidence that mesoscopic changes precede visually detected macroscopic phase separation in aqueous mixtures of two polymers and a single polymer and salt. Dynamic light scattering (DLS) analysis indicates the formation of mesoscopic polymer agglomerates in these systems. These agglomerates increase in size with increasing polymer concentrations prior to visual phase separation. Such mesoscopic changes are paralleled by changes in water structure as evidenced by Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) spectroscopic analysis of OH-stretch bands. Through OH-stretch band analysis, we obtain quantitative estimates of the relative fractions of four subpopulations of water structures coexisting in aqueous solutions. These estimates indicate that abrupt changes in hydrogen bond arrangement take place at concentrations below the threshold of macroscopic phase separation. We used these experimental observations to develop a model of phase separation in aqueous media.

Systematic Parameterization of Ion-Surfactant Interactions in Dissipative Particle Dynamics Using Setschenow Coefficients

Dissipative particle dynamics (DPD) simulations of nonionic surfactants with an added salt show that the Setschenow relationship is reproduced; that is, the critical micelle concentration is log-linearly dependent on the added salt concentration. The simulated Setschenow coefficients depend on the DPD bead–bead repulsion amplitudes, and matching to the experimentally determined values provides a systematic method to parameterize the interactions between salt ion beads and surfactant beads. The optimized ion-specific interaction parameters appear to be transferrable and follow the same trends as the empirical Hofmeister series.

Linear Relationships between Partition Coefficients of Different Organic Compounds and Proteins in Aqueous Two-Phase Systems of Various Polymer and Ionic Compositions

Analysis of the partition coefficients of small organic compounds and proteins in different aqueous two-phase systems under widely varied ionic compositions shows that logarithms of partition coefficients for any three compounds or proteins or two organic compounds and one protein are linearly interrelated, although for protein(s) there are ionic compositions when the linear fit does not hold. It is suggested that the established interrelationships are due to cooperativity of different types of solute-solvent interactions in aqueous media. This assumption is confirmed by analysis of distribution coefficients of various drugs in octanol-buffer systems with varied ionic compositions of the buffer. Analysis of the partition coefficients characterizing distribution of variety of drugs between blood and different tissues of rats in vivo reported in the literature showed that the above assumption is correct and enabled us to identify the tissues with the components of which the drug(s) may engage in presumably direct interactions. It shows that the suggested assumption is valid for even complex biological systems.

Salt-containing aqueous two-phase system shows predictable partition of proteins with surface amino acids residues

Aqueous two-phase system (ATPS) containing salts has been used for protein purification and enrichment. However, it is unclear how proteins are partitioned in the top or bottom phases of the system. In this study, we demonstrate that the partition of proteins in salt-containing ATPS (SATPS) depends only on the relation between the protein-surface amino acids and the type of salt using SATPS. The partition coefficients of four proteins changed depending on the kind of salt, according to the Hofmeister series. Interestingly, the partition coefficients of the proteins correlated to those of the combination of the amino acids in the surface of the protein with the correlation coefficients of >0.9. The results suggest that the interaction between the protein surface and aqueous ions plays an indispensable role for the partition of proteins in SATPS that can help in the design of protein partition in ATPS for purification and enrichment.

Aqueous Two-Phase Systems at Large Scale: Challenges and Opportunities

Aqueous two-phase systems (ATPS) have proved to be an efficient and integrative operation to enhance recovery of industrially relevant bioproducts. After ATPS discovery, a variety of works have been published regarding their scaling from 10 to 1000 L. Although ATPS have achieved high recovery and purity yields, there is still a gap between their bench-scale use and potential industrial applications. In this context, this review paper critically analyzes ATPS scale-up strategies to enhance the potential industrial adoption. In particular, large-scale operation considerations, different phase separation procedures, the available optimization techniques (univariate, response surface methodology, and genetic algorithms) to maximize recovery and purity and economic modeling to predict large-scale costs, are discussed. ATPS intensification to increase the amount of sample to process at each system, developing recycling strategies and creating highly efficient predictive models, are still areas of great significance that can be further exploited with the use of high-throughput techniques. Moreover, the development of novel ATPS can maximize their specificity increasing the possibilities for the future industry adoption of ATPS. This review work attempts to present the areas of opportunity to increase ATPS attractiveness at industrial levels.

The solvent side of proteinaceous membrane-less organelles in light of aqueous two-phase systems

Water represents a common denominator for liquid-liquid phase transitions leading to the formation of the polymer-based aqueous two-phase systems (ATPSs) and a set of the proteinaceous membrane-less organelles (PMLOs). ATPSs have a broad range of biotechnological applications, whereas PMLOs play a number of crucial roles in cellular compartmentalization and often represent a cellular response to the stress. Since ATPSs and PMLOs contain high concentrations of polymers (such as polyethylene glycol (PEG), polypropylene glycol (PPG), Ucon, and polyvinylpyrrolidone (PVP), Dextran, or Ficoll) or biopolymers (peptides, proteins and nucleic acids), it is expected that the separated phases of these systems are characterized by the noticeable changes in the solvent properties of water. These changes in solvent properties can drive partitioning of various compounds (proteins, nucleic acids, organic low-molecular weight molecules, metal ions, etc.) between the phases of ATPSs or between the PMLOs and their surroundings. Although there is a sizable literature on the properties of the ATPS phases, much less is currently known about PMLOs. In this perspective article, we first represent liquid-liquid phase transitions in water, discuss different types of biphasic (or multiphasic) systems in water, and introduce various PMLOs and some of their properties. Then, some basic characteristics of polymer-based ATPSs are presented, with the major focus being on the current understanding of various properties of ATPS phases and solvent properties of water inside them. Finally, similarities and differences between the polymer-based ATPSs and biological PMLOs are discussed.

In Aqua Veritas: The Indispensable yet Mostly Ignored Role of Water in Phase Separation and Membrane-less Organelles

Despite the common practice of presenting structures of biological molecules on an empty background and the assumption that interactions between biological macromolecules take place within the inert solvent, water represents an active component of various biological processes. This Perspective addresses indispensable, yet mostly ignored, roles of water in biological liquid-liquid phase transitions and in the biogenesis of various proteinaceous membrane-less organelles. We point out that changes in the structure of water reflected in the changes in its abilities to donate and/or accept hydrogen bonds and participate in dipole-dipole and dipole-induced dipole interactions in the presence of various solutes (ranging from small molecules to synthetic polymers and biological macromolecules) might represent a driving force for the liquid-liquid phase separation, define partitioning of various solutes in formed phases, and define the exceptional ability of intrinsically disordered proteins to be engaged in the formation of proteinaceous membrane-less organelles.

Effects of osmolytes on protein-solvent interactions in crowded environment: Analyzing the effect of TMAO on proteins in crowded solutions

We analyzed the effect of a natural osmolyte, trimethylamine N-oxide (TMAO), on structural properties and conformational stabilities of several proteins under macromolecular crowding conditions by a set of biophysical techniques. We also used the solvent interaction analysis method to look at the peculiarities of the TMAO-protein interactions under crowded conditions. To this end, we analyzed the partitioning of these proteins in TMAO-free and TMAO-containing aqueous two-phase systems (ATPSs). These ATPSs had the same polymer composition of 6.0 wt.% PEG-8000 and 12.0 wt.% dextran-75, and same ionic composition of 0.01 M K/NaPB, pH 7.4. These analyses revealed that there is no direct interaction of TMAO with proteins, suggesting that the TMAO effects on the protein structure in crowded solutions occur via the effects of this osmolyte on solvent properties of aqueous media. The effects of TMAO on protein structure in the presence of polymers were rather complex and protein-specific. Curiously, our study revealed that in highly concentrated polymer solutions, TMAO does not always act to promote further protein folding.

Analyzing the effects of protecting osmolytes on solute–water interactions by solvatochromic comparison method: I. Small organic compounds

Solvent properties of water in aqueous solutions of osmolytes (sorbitol, sucrose, trehalose, and trimethylamine N-oxide (TMAO)) were studied at different concentrations using the solvatochromic comparison method.

Effect of ionic composition on the partitioning of organic compounds in octanol–buffer systems

The ionic composition of octanol–buffer systems might have significant effects on the distribution of organic compounds. Their responses to ionic environments follow the relationships established previously in organic solvent-free aqueous solutions.

Effects of osmolytes on protein–solvent interactions in crowded environments: study of sucrose and trehalose effects on different proteins by solvent interaction analysis

The logarithms of the partition coefficients of proteins in the presence of 0.5 M sucrose and trehalose are linearly interrelated.

Analyzing the effects of protecting osmolytes on solute–water interactions by solvatochromic comparison method: II. Globular proteins

Partitioning of 11 globular proteins was examined in aqueous dextran–PEG–sodium/potassium phosphate buffer (0.01 M K/NaPB, pH 7.4) two-phase systems (ATPSs) containing 0.5 M sorbitol.

Potential application of aqueous two-phase systems and three-phase partitioning for the recovery of superoxide dismutase from a clarified homogenate of Kluyveromyces marxianus

Superoxide dismutase (SOD; EC 1.15.1.1) is an antioxidant enzyme that represents the primary cellular defense against superoxide radicals and has interesting applications in the medical and cosmetic industries. In the present work, the partition behavior of SOD in aqueous two-phase systems (ATPS) (using a standard solution and a complex extract from Kluyveromyces marxianus as sample) was characterized on different types of ATPS (polymer-polymer, polymer-salt, alcohol-salt, and ionic liquid (IL)-salt). The systems composed of PEG 3350-potassium phosphate, 45% TLL, 0.5 M NaCl (315 U/mg, 87% recovery, and 15.1-fold purification) and t-butanol-20% ammonium sulfate (205.8 U/mg, 80% recovery and 9.8-fold purification), coupled with a subsequent 100 kDa ultrafiltration stage, allowed the design of a prototype process for the recovery and partial purification of the product of interest. The findings reported herein demonstrate the potential of PEG-salt ATPS for the potential recovery of SOD.

Origin of salt additive effect on solute partitioning in aqueous polyethylene glycol-8000-sodium sulfate two-phase system

Partitioning of a homologous series of dinitrophenylted (DNP-) amino acids with aliphatic side chains was examined in aqueous polyethylene glycol (PEG)-8000-sodium sulfate two-phase systems (ATPS) with the additives NaSCN, NaClO4, and NaH2PO4 at concentrations varied from 0.025M up to 0.54M. The differences between the relative hydrophobicities and electrostatic properties of the two phases in all ATPS were estimated. Partitioning of adenine, adenosine mono-, di- and tri-phosphates was also examined in all ATPSs, including those with NaCl additive. Partition coefficients for these compounds and for nonionic organic compounds previously reported [L.A. Ferreira, P. Parpot, J.A. Teixeira, L.M. Mikheeva, B.Y. Zaslavsky, J. Chromatogr. A 1220 (2012) 14.] were analyzed in terms of linear solvent regression relationship. The results obtained suggest that the effects of the salts additives are related to their influence on the water structure.

Membrane-free electroextraction using an aqueous two-phase system

We present a method of continuous electroextraction of amino acids using aqueous two phase system in a microchip. The separations occur due to differences in electrophoretic mobility and solvent affinity. The results suggest the possibility of high levels of purification by controlling the electric field across the liquid barrier.

Solvent interaction analysis of intrinsically disordered proteins in aqueous two-phase systems

In an aqueous two-phase system (ATPS), the partitioning of a protein is defined by the differential interactions of the protein with aqueous media in the two phases. Our study shows that partitioning of proteins in a set of ATPSs of different ionic compositions can be used to quantify structural differences between α-synuclein, its variants and several globular proteins. Since application of ATPSs implies the use of high concentrations of two polymers in water when a certain threshold concentration of the polymers is exceeded, and since these levels of polymer concentrations are similar to those commonly used to mimic the effects of macromolecular crowding on proteins, we used circular dichroism spectroscopy to evaluate the structural consequences of placing proteins in solutions with high polymer concentrations and various ionic compositions.