Changes In Electrostatic Interactions Research Articles

Spatioselective Occlusion of Copolymer Nanoparticles within Calcite Crystals Generates Organic-Inorganic Hybrid Materials with Controlled Internal Structures.

Efficient occlusion of particulate additives into a single crystal has garnered an ever-increasing attention in materials science because it offers a counter-intuitive yet powerful platform to make crystalline nanocomposite materials with emerging properties. However, precisely controlling the spatial distribution of the guest additives within a host crystal remains highly challenging. We herein demonstrate a unique, straightforward method to engineer the spatial distribution of copolymer nanoparticles within calcite (CaCO3) single crystals by judiciously adjusting initial [Ca2+] concentration used for the calcite precipitation. More specifically, polymerization-induced self-assembly is employed to synthesize well-defined and highly anionic poly(3-sulfopropyl methacrylate potassium)41-block-poly(benzyl methacrylate)500 [PSPMA41-PBzMA500] diblock copolymer nanoparticles, which are subsequently used as model additives during the growth of calcite crystals. Impressively, such guest nanoparticles are preferentially occluded into specific regions of calcite depending on the initial [Ca2+] concentration. These unprecedented phenomena are most probably caused by dynamic change in electrostatic interaction between Ca2+ ions and PSPMA41 chains based on systematic investigations. This study not only showcases a significant advancement in controlling the spatial distribution of guest nanoparticles within host crystals, enabling the internal structure of composite crystals to be rationally tailored via a spatioselective occlusion strategy, but also provides new insights into biomineralization.

Spatioselective Occlusion of Copolymer Nanoparticles within Calcite Crystals Generates Organic‐Inorganic Hybrid Materials with Controlled Internal Structures

Efficient occlusion of particulate additives into a single crystal has garnered an ever‐increasing attention in materials science because it offers a counter‐intuitive yet powerful platform to make crystalline nanocomposite materials with emerging properties. However, precisely controlling the spatial distribution of the guest additives within a host crystal remains highly challenging. We herein demonstrate a unique, straightforward method to engineer the spatial distribution of copolymer nanoparticles within calcite (CaCO3) single crystals by judiciously adjusting initial [Ca2+] concentration used for the calcite precipitation. More specifically, polymerization‐induced self‐assembly is employed to synthesize well‐defined and highly anionic poly(3‐sulfopropyl methacrylate potassium)41‐block‐poly(benzyl methacrylate)500 [PSPMA41‐PBzMA500] diblock copolymer nanoparticles, which are subsequently used as model additives during the growth of calcite crystals. Impressively, such guest nanoparticles are preferentially occluded into specific regions of calcite depending on the initial [Ca2+] concentration. These unprecedented phenomena are most probably caused by dynamic change in electrostatic interaction between Ca2+ ions and PSPMA41 chains based on systematic investigations. This study not only showcases a significant advancement in controlling the spatial distribution of guest nanoparticles within host crystals, enabling the internal structure of composite crystals to be rationally tailored via a spatioselective occlusion strategy, but also provides new insights into biomineralization.

Graphene as a potential treatment for acute migraine: A computational study

Here, we study the graphene nanosheets with various functional groups including –COOH, -NH2, –COOH-NH2, -OH, and O interacting with calcitonin receptor-like receptor (CLR) in combination with receptor activity-modifying protein (RAMP1). This study uses molecular dynamics (MD) simulations to study the interaction between CLR/RAMP1 and graphene-family planar nanosheets: Gr, Gr-COOH, Gr-NH2, Gr-OH, Gr-O, and Gr-COOH&-NH2. The Ubrogepant was used to validate the results and comparison of the Gr-family performance. The MD simulation data revealed that Gr, Gr-OH, and Gr-COOH interacted with CLR/RAMP1 more intensely, due to changes in electrostatic interactions. Furthermore, the binding affinity of the nanosheets, as well as Ubrogepant toward the protein, have been calculated using docking. Docking analysis with both CLR fragment and CLR/RAMP1revealed similar trends in the interactions where Gr-OH has the strongest affinity in binding to the neuropeptide. The DFT calculations demonstrated a discernible surface polarity hierarchy among the functionalized graphene materials, revealing Gr-O and Gr-OH with the highest surface polarity, followed by Gr-COOH and Gr-NH2, respectively, consistent with our findings. Altogether, our study shows that three candidates; Gr-OH> Gr-COOH> pristine Gr can inhibit CGRPR binding by disrupting the protein’s structure. Significantly, the Gr-family outperformed Ubrogepant as an indicator of its potential anti-migraine applications. The results of this study provide detailed and reliable theoretical guidance for using the graphene family in treating migraine and can assist in the further development of new graphene-based materials.

Electrostatic interactions of enzymes in non-aqueous conditions: insights from molecular dynamics simulations

Electrostatic interactions of enzymes and their effects on enzyme activity and stability are poorly understood in non-aqueous conditions. Here, we investigate the contribution of the electrostatic interactions on the stability and activity of enzymes in the non-aqueous environment using molecular dynamics simulations. Lipase was selected as active and lysozyme as inactive model enzymes in non-aqueous media. Hexane was used as a common non-aqueous solvent model. In agreement with the previous experiments, simulations show that lysozyme has more structural instabilities than lipase in hexane. The number of hydrogen bonds and salt bridges of both enzymes is dramatically increased in hexane. In contrast to the other opinions, we show that the increase of the electrostatic interactions in non-aqueous media is not so favorable for enzymatic function and stability. In this condition, the newly formed hydrogen bonds and salt bridges can partially denature the local structure of the enzymes. For lysozyme, the changes in electrostatic interactions occur in all domains including the active site cleft, which leads to enzyme inactivation and destabilization. Interestingly, most of the changes in electrostatic interactions of lipase occur far from the active site regions. Therefore, the active site entrance regions remain functional in hexane. The results of this study reveal how the changes in electrostatic interactions can affect enzyme stability and activity in non-aqueous conditions. Moreover, we show for the first time how some enzymes, such as lipase, remain active in a non-aqueous environment. Communicated by Ramaswamy H. Sarma

Omicron variant and change of electrostatic interactions between receptor binding domain of severe acute respiratory syndrome coronavirus 2 with the angiotensin-converting enzyme 2 receptor.

BACKGROUNDSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants are currently a new hazard. Since the first appearance of classical SARS-CoV-2 in late 2019, pathogen genetic alterations have continued to occur, and some new hazardous forms have already emerged. The underlying pathophysiological process leading to clinical issue is molecular change caused by genetic mutation. AIMTo determine the change in the interaction between receptor binding domain of omicron variant SARS-CoV-2 and the angiotensin-converting enzyme 2 (ACE2). METHODSThe researchers investigated how alterations in the binding area of the SARS receptor CoV2 interacted electrostatically with the ACE2 receptor. In this report, three important coronavirus disease 2019 variants, beta, delta, and omicron, were investigated. RESULTSAccording to this study, there was a change of electrostatic interactions between the receptor binding domain of SARS-CoV-2 with the ACE2 receptor due to each studied variant. The most change was detected in omicron variant followed by delta variant and beta variant.CONCLUSIONOur results may support the clinical finding that the omicron variant is more transmissible than the wild type and other variants.

Intrinsic defects in primary halide perovskites: A first-principles study of the thermodynamic trends

Defects in halide perovskites play an essential role in determining the efficiency and stability of the optoelectronic devices based on these materials. We present a systematic study of intrinsic point defects in six primary metal halide perovskites, ${\mathrm{MAPbI}}_{3}, {\mathrm{MAPbBr}}_{3}, {\mathrm{MAPbCl}}_{3}, {\mathrm{FAPbI}}_{3}, {\mathrm{CsPbI}}_{3}$, and ${\mathrm{MASnI}}_{3}$ (where MA denotes methylammonium and FA denotes formamidinium), based upon density functional theory calculations. Within a single computational scheme, using the $\text{SCAN}+\text{rVV10}$ functional, we compare the impact of changing anions and cations on the defect formation energies and the charge state transition levels in the six compounds, and identify the physical origins underlying the observed trends. Dominant defects in the lead iodide compounds are the ${A}^{+}$ cation interstitials ($A=\text{Cs}$, MA, FA), charge-compensated by ${\mathrm{I}}^{\ensuremath{-}}$ interstitials or lead $(2\ensuremath{-})$ vacancies. In the lead bromide and lead chloride compounds, halide interstitials are most prominent, and for ${\mathrm{MAPbCl}}_{3}$, the chlorine vacancy also becomes important. These trends can be explained in terms of the changes in electrostatic interactions and chemical bonding upon replacing cations and anions. Defect physics in ${\mathrm{MASnI}}_{3}$ is strongly dominated by tin $(2\ensuremath{-})$ vacancies, promoted by the easy oxidation of the tin. Intrinsically, all compounds are mildly $p$ doped, except for ${\mathrm{MASnI}}_{3}$, which is strongly $p$ doped. All acceptor levels created by defects in the six perovskites are shallow. Some defects, halide vacancies and Pb or Sn interstitials in particular, can create deep donor traps. Although such traps might hamper the electronic behavior of ${\mathrm{MAPbCl}}_{3}$, in bromine- and iodine-based perovskites their equilibrium concentrations are too small to affect the materials' properties.

Experimental and theoretical investigation on the adsorption properties of benzene on graphene surface: Influence of pH and edge effects

Graphene materials, as drug carriers, play an important role in the specific drug delivery system. The drug molecules with aromatic structures can be adsorbed on the surface of graphene in vitro through π-π stacking interaction and released directionally at the lesion under special temperature and pH-value environment. This paper proposes a new experimental method and theoretical model for the purpose to study the effect and mechanism of environmental pH and edge of graphene on the adsorption mechanical properties between graphene and benzene. The experimental results based on atomic force microscope show that the acidic environment is more conducive to the adsorption of benzene on the surface of graphene than the alkaline environment. The adsorption performance of benzene at the center of graphene is better than that at the edge. Moreover, based on experimental results, mechanisms of pH effect and edge effect are revealed by potential function theory. The pH effect is influenced by the change of electrostatic interaction in different pH environments. In addition, edge effect is mainly dominated by van der Waals interaction. This study solves the problem of specific influence mechanism of pH on π-π stacking interaction using mechanical means for the first time, and shows that graphene as a drug carrier has strong pH response characteristics and great application potential.

Electrochemical Sensing of Interactions between DNA and Charged Macrocycles

In this work, we investigated aggregation of native DNA and thiacalix[4]arene derivative bearing eight terminal amino groups in cone configuration using various redox probes on the glassy carbon electrode. It was shown that sorption transfer of the aggregates on the surface of the electrode covered with carbon black resulted in changes in electrostatic interactions and diffusional permeability of the surface layer. Such changes alter the signals of ferricyanide ion, methylene green and hydroquinone as redox probes to a degree depending on their specific interactions with DNA and own charge. Inclusion of DNA in the surface layer was independently confirmed by scanning electron microscopy, electrochemical impedance spectroscopy and experiments with doxorubicin as a model intercalator. Thermal denaturing of DNA affected the charge separation on the electrode interface and the signals of redox probes. Using hydroquinone, less sensitive to electrostatic interactions, made it possible to determine from 10 pM to 1.0 nM doxorubicin (limit of detection 3 pM) after 10 min incubation. Stabilizers present in the commercial medications did not alter the signal. The DNA sensors developed can find future application in the assessment of the complexes formed by DNA and macrocycles as delivery agents for small chemical species.

Molecular mechanism of methyl-dependent and spatial-specific DNA recognition of c-Jun homodimer.

DNA methylation is important in regulation of gene expression and normal development because it alters the interplay between protein and DNA. Experiments have shown that a single 5-methylcytosine at different CpG sites (mCpG) might have different effects on specific recognition, but the atomistic origin and dynamic details are largely unclear. In this work, we investigated the mechanism of monomethylation at different CpG sites in the cognate motif and the cooperativity of full methylation. By constructing four models of c-Jun/Jun protein binding to the 5[Formula: see text]-XGAGTCA-3[Formula: see text] (X represents C or methylated C) motif, we characterized the dynamics of the contact interface using the all-atom molecular dynamics method. Free energy analysis of MM/GBSA suggests that regardless of whether the C12pG13 site of the bottom strand is methylated, the effects from mC25 of the top strand are dominant and can moderately enhance the binding by [Formula: see text] 31 kcal/mol, whereas mC12 showed a relatively small contribution, in agreement with the experimental data. Remarkably, we found that this spatial-specific influence was induced by different regulatory rules. The influence of the mC25 site is mainly mediated by steric hindrance. The additional methyl group leads to the conformational changes in nearby residues and triggers an obvious structural bending in the protein, which results in the formation of a new T-Asn-C triad that enhances the specific recognition of TCA half-sites. The substitution of the methyl group at the mC12 site of the bottom strand breaks the original H-bonds directly. Such changes in electrostatic interactions also lead to the remote allosteric effects of protein by multifaceted interactions but have negligible contributions to binding. Although these two influence modes are different, they can both fine-tune the local environment, which might produce remote allosteric effects through protein-protein interactions. Further analysis reveals that the discrepancies in these two modes are primarily due to their location. Moreover, when both sites are methylated, the major determinant of binding specificity depends on the context and the location of the methylation site, which is the result of crosstalk and cooperativity.

Effect of H2O Molecules on the CO2 Replacement in CH4 Hydrate Behavior by Molecular Simulation

CH₄–CO₂ replacement technology has broad application prospects in reducing CO₂ emission and developing natural gas hydrate (NGH) resources. It is of great significance to study the mechanism of CH₄–CO₂ replacement. In this paper, the effect of H₂O on CH₄–CO₂ displacement behavior is studied by molecular dynamics (MD) simulation and quantum mechanics calculation. The interactions between the host and guest in cages of CH₄ hydrate are calculated using the symmetry-adapted perturbation theory method. The contribution of physical components of binding energy can be determined. The result indicates that the electrostatic interaction of H₂O–H₂O and H₂O–gas is a key factor of the CH₄–CO₂ replacement mechanism. Additionally, the microconfigurations and microstructure properties are analyzed by MD simulation in the systems containing a gas layer (CO₂ or CH₄) and a CH₄ hydrate layer. The results showed that the movement and the arrangement of H₂O molecules influence the hydrate structure due to the interaction of H₂O–gas during the replacement process. The molecular simulation suggests that the change of electrostatic interaction with H₂O molecules could improve the CH₄–CO₂ replacement efficiency, which can be favorable for the investigation of CH₄ replacement technology in NGH with CO₂ injection.

Adsorption of Myoglobin and Corona Formation on Silica Nanoparticles.

The adsorption of proteins from aqueous medium leads to the formation of protein corona on nanoparticles. The formation of protein corona is governed by a complex interplay of protein–particle and protein–protein interactions, such as electrostatics, van der Waals, hydrophobic, hydrogen bonding, and solvation. The experimental parameters influencing these interactions, and thus governing the protein corona formation on nanoparticles, are currently poorly understood. This lack of understanding is due to the complexity in the surface charge distribution and anisotropic shape of the protein molecules. Here, we investigate the effect of pH and salinity on the characteristics of corona formed by myoglobin on silica nanoparticles. We experimentally measure and theoretically model the adsorption isotherms of myoglobin binding to silica nanoparticles. By combining adsorption studies with surface electrostatic mapping of myoglobin, we demonstrate that a monolayered hard corona is formed in low salinity dispersions, which transforms into a multilayered hard + soft corona upon the addition of salt. We attribute the observed changes in protein adsorption behavior with increasing pH and salinity to the change in electrostatic interactions and surface charge regulation effects. This study provides insights into the mechanism of protein adsorption and corona formation on nanoparticles, which would guide future studies on optimizing nanoparticle design for maximum functional benefits and minimum toxicity.

Heparin-Coated Albumin Nanoparticles for Drug Combination in Targeting Inflamed Intestine.

Targeting areas of inflammation offers potential therapeutic and diagnostic benefits by maximizing drug and imaging marker on-target effects while minimizing systemic exposure that can be associated with adverse side effects. This strategy is particularly beneficial in the management of inflammatory bowel disease (IBD). Here an inflammation-targeting (IT) approach based on heparin-coated human serum albumin nanoparticles (HEP-HSA NPs) that utilize the increased intestinal permeability and changes in electrostatic interaction at the site of intestinal inflammation is described. Using small-molecule and biologic drugs as a model for drug combination, the HEP-HSA NPs demonstrate the capacity to load both drugs simultaneously; the dual-drug loaded HEP-HSA NPs exhibit a higher anti-inflammatory effect than both of the single-drug loaded NPs in vitro and selectively bind to inflamed intestine after enema administration in vivo in a murine model of colitis. Importantly, analyses of the physicochemical characteristics and targeting capacities of these NPs indicate that HEP coating modulates NP binding to the inflamed intestine, providing a foundation for future IT-NP formulation development.

Interactions of Chlorella vulgaris and fly ash cenospheres in heat-aided ballasted flotation

Heat-aided ballasted flotation using industrial waste heat is a cost-effective and eco-friendly technology to harvest microalgae from aquatic environment. However, the underlying mechanism of this process is not yet fully understood. This study investigates the interactions between Chlorella vulgaris and fly ash cenospheres in heat-aided ballasted flotation based on the Extended Derjaguin-Landau-Verwey-Overbeek approach. The results indicated that Lifshitz-van der Waals interaction played an important role in the attachment of algal cell on fly ash cenospheres. Furthermore, the Lewis acid-base interaction changed from repulsion to attraction in the system due to heating, which promoted the algal cells to attach on fly ash cenospheres, resulting in a higher harvesting efficiency. However, when the temperature was increased to 90 °C, the Lifshitz-van der Waals interaction was reversed, which resulted in an energy barrier. The total attractive interaction increased with the decrease in pH from 10 to 4, due to changes in electrostatic interaction. After surface modification of fly ash cenospheres, the electrostatic interaction was always attractive in this system at pH of 7 regardless of temperature variations. Finally, according to the experimental results and the Extended Derjaguin-Landau-Verwey-Overbeek analysis, the usage of surface modified fly ash cenospheres for heat-aided ballasted flotation can be advantageous for environmental safety and high efficiency.

Stimuli-responsive adsorption behavior toward heavy metal ions based on comb polymer functionalized magnetic nanoparticles

A novel type of poly(maleic anhydride)-graft-poly(vinyl alcohol) comb polymer functionalized magnetic nanoparticles was specially designed and prepared as an efficient adsorbent with stimuli-responsive reversible adsorption/desorption behavior for the controllable removal of heavy metal ions. The adsorption capacities of comb polymer functionalized magnetic nanoparticles toward Ag+, Ni2+, Cd2+, Pb2+ and Co2+, exhibiting good fits to Langmuir isotherm model and Pseudo-second order kinetic model with correlation coefficients of more than 0.98, were 0.8634, 0.8194, 0.8429, 0.6720 and 0.7682 mmol g−1 respectively, which were 5 times greater than those of linear polymer functionalized magnetic nanoparticles due to the contribution of topology evolution. Furthermore, the uptake rate of comb polymer functionalized magnetic nanoparticles toward Ag+, Ni2+, Cd2+, Pb2+ and Co2+ increased significantly from 21.1%, 17.6%, 18.64%, 16.3% and 15.68% to 92.15%, 89.2%, 90.16%, 83.56% and 84.52% respectively when the solution pH increases from 4 to 7, showing a pH-responsive characteristic, the mechanism of which was elucidated as the pH-driven changes in electrostatic interaction and molecular morphology. Good sustainability and facile reusability were practically reflected by over 80% uptake efficiency after 5 consecutive absorption/desorption cycles. The innovation of this work is that changing molecular topological structure of the polymer can significantly contribute to excellent adsorption capacity and pH responsiveness to remove heavy metal ions in wastewater. The importance of this study is to offer a practical cleaner production process for an attractive adsorbent with stimuli-responsive adsorption behavior and good sustainable application through innovative molecular design.

Reversibly pH-responsive gold nanoparticles and their applications for photothermal cancer therapy

Microenvironment responsive nanomaterials are attractive for therapeutic applications with regional specificity. Here we report pH responsive gold nanoparticles which are designed to aggregate in acidic condition similar to cancer environment and returned to its original disassembled states in a physiological pH. The pH responsive behavior of the particles is derived by change of electrostatic interaction among the particles where attraction and repulsion play a major role in low and high pH of the environment, respectively. Since different electrostatic interaction behavior of the particles in varied pH is induced not by irreversible chemical change but by simple protonation differences, the pH responsive process of assembly and disassembly is totally reversible. The low pH specific aggregation of gold nanoparticles resulted in red shift of plasmonic absorption peak and showed higher photothermal efficacy in acidic pH than in normal physiological pH. The low pH specific photothermal effect with long wave laser irradiation was directly applied to cancer specific photothermal therapy and resulted higher therapeutic effect for melanoma cancer cells than non-pH responsive gold nanoparticles.

Effects of High Pressure Modification on Conformation and Digestibility Properties of Oyster Protein.

To expand the utilization of oyster protein (OP), the effects of high pressure (100 to 500 MPa) on chemical forces, structure, microstructure, and digestibility properties were investigated. High pressure (HP) treatment enhanced the electrostatic repulsion (from −13.3Control to −27.8HP200 mV) between protein molecules and avoided or retarded the formation of protein aggregates. In addition, the HP treated samples showed uniform distribution and small particle size. The changes in electrostatic interaction and particle size contributed to the improvement of solubility (from 10.53%Control to 19.92%HP500 at pH 7). The stretching and unfolding of protein were modified by HP treatment, and some internal hydrophobic groups and -SH groups were exposed. HP treatment modified the secondary structure of OP. The treated samples contained less α-helix and β-sheet structures, whereas the proportions of β-sheet and random coil structures were increased. The treated samples have high digestibility in the stomach (from 26.3%Control to 39.5%HP500) and in the total digestive process (from 62.1%Control to 83.7%HP500). In addition, the total digestive production showed higher percentages of small peptides (<1 kDa) after HP treatment. The protein solubility and digestibility were increased after HP treatment, and high solubility and high digestibility might increase the chance that OP become a kind of protein supplement.

Heat-induced gel formation of a protein-rich extract from the microalga Chlorella sorokiniana

Abstract Microalgae proteins are an underutilized biomass source for foods with unknown technofunctionalities. Heat-induced gel formation was used in this study to investigate the gelation properties of a protein-rich extract from the microalga Chlorella sorokiniana. Gel formation was achieved at a minimum protein concentration of 9.9 g/100 mL and a temperature of 61 °C was necessary to produce a stable gel network. Small-amplitude oscillatory shear measurements revealed that a weak gel was formed with tan δ > 0.1, which was also evident during backward extrusion measurements. The elasticity of the gels increased when the final Tset was increased and a maximum gel elasticity was obtained at Tset = 80 °C and a heating rate of 1 °C min−1. Increasing the heating rate to 5 and 15 °C min−1 negatively affected the gel strength. Additionally, increasing the ionic-strength and increasing or decreasing the pH negatively affected the gel network, which was related to a change in electrostatic interactions. The results obtained showed that it is possible to produce protein gels from water-soluble protein-rich extracts from Chlorella sorokiniana, which may simplify application of protein extracts from this microalga in foods.

Designing Electrostatic Interactions via Polyelectrolyte Monomer Sequence.

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.

Molecular dynamics simulations suggest changes in electrostatic interactions as a potential mechanism through which serine phosphorylation inhibits DNA polymerase β activity

DNA polymerase β is a 39 kDa enzyme that is a major component of Base Excision Repair in human cells. The enzyme comprises two major domains, a 31 kDa domain responsible for the polymerase activity and an 8 kDa domain, which bind ssDNA and has a deoxyribose phosphate (dRP) lyase activity. DNA polymerase β was shown to be phosphorylated in vitro with protein kinase C (PKC) at serines 44 and 55 (S44 and S55), resulting in loss of its polymerase enzymic activity, but not its ability to bind ssDNA. In this study, we investigate the potential phosphorylation-induced structural changes for DNA polymerase β using molecular dynamics simulations. The simulations show drastic conformational changes of the polymerase structure as a result of S44 phosphorylation. Phosphorylation-induced conformational changes transform the closed (active) enzyme structure into an open one. Further analysis of the results points to a key hydrogen bond and newly formed salt bridges as potential drivers of these structural fluctuations. The changes observed with S55/44 and S55 phosphorylation were less dramatic and the integrity of the H-bond was not compromised. Thus the phosphorylation of S44 is the major contributor to structural fluctuations that lead to loss of enzymatic activity.

Interactions and phase behaviors in mixed solutions of κ-carrageenan and myofibrillar protein extracted from Alaska Pollock surimi

In the present work, we provide insight into electrostatic interactions and phase behaviors in mixtures of myofibrillar protein (MP) and κ-carrageenan (KC) of various pHs (8.0–3.0) and biopolymer weight ratios [R, from 1:1 to 20:1; total concentration=0.05% (w/w)] through turbidimetric analysis, dynamic light scattering (DLS) and zeta potential analysis, and optical microscopy. At R=1: 1, critical pH values (i.e., pHc, pHΦ1, and pHΦ2), which indicate phase transitions interrelated to the formation of soluble or insoluble MP-KC complexes, were observed at pH7.6, 6.8, and 3.6, respectively. As the ratio increased, the pHmax shifted from 4.9 to 5.8. A similar trend was observed for the isoelectric point of MP-KC mixtures, as determined by zeta potential measurements. The maximum interaction indicated by the highest turbidity occurred at pHmax=5.3, at a ratio of 5:1, whereas pHc remained constant during acidification. The changes in electrostatic interactions and transformations of phase behaviors accompanying the complex formation and disassociation processes were further supported by particle size distribution analysis and optical microscopic observations of MP-KC mixtures (R=1:1) at different pH values. This work fills the previous lack of studies on phase behaviors of surimi protein and colloidal polysaccharide in liquid system, and lay the foundation to provide a new way to solve problems of interactions between protein and polysaccharide during the processing of surimi products.