Macromolecular Aggregates Research Articles

Effect of low-sodium salt on the physicochemical and rheological properties of wheat flour doughs and their respective gluten

Reducing sodium in cereal products has become a health trend, and low-sodium salt is considered as a promising sodium substitute; however, its technical roles in dough formation have not been well understood. Effects of low-sodium salt on the physicochemical and rheological properties of dough were investigated in the present study compared with that with NaCl and KCl. Addition of low-sodium salt significantly increased stability, development time and extensional area of dough, and reduced water absorption. Wheat gluten extractability and free SH content gradually decreased with low-sodium salt additions increased, indicating that salt affected gluten macromolecular aggregation. Zeta potential measurements indicated that salt promoted the interactions between gluten molecules. Overall, low-sodium salt effectively changed physicochemical and rheological properties of dough in a manner very similar to NaCl and KCl. Therefore, addition of low-sodium salt may be a feasible approach to alleviate high sodium in the process of dough formation.

Hyaluronic acid synthesis, degradation, and crosslinking in equine osteoarthritis: TNF-\u03b1-TSG-6-mediated HC-HA formation

BackgroundTNF-α-stimulated gene 6 (TSG-6) protein, a TNF-α-responsive hyaladherin, possesses enzymatic activity that can catalyze covalent crosslinks of the polysaccharide hyaluronic acid (HA) to another protein to form heavy chain-hyaluronic acid (HC-HA) complexes in pathological conditions such as osteoarthritis (OA). Here, we examined HA synthase and inflammatory gene expression; synovial fluid HA, TNF-α, and viscosity; and TSG-6-mediated HC-HA complex formation in an equine OA model. The objectives of this study were to (1) evaluate the TNF-α-TSG-6-HC-HA signaling pathway across multiple joint tissues, including synovial membrane, cartilage, and synovial fluid, and (2) determine the impact of OA on synovial fluid composition and biophysical properties.MethodsHA and inflammatory cytokine concentrations (TNF-α, IL-1β, CCL2, 3, 5, and 11) were analyzed in synovial fluid from 63 OA and 25 control joints, and HA synthase (HAS1-3), TSG-6, and hyaluronan-degrading enzyme (HYAL2, HEXA) gene expression was measured in synovial membrane and cartilage. HA molecular weight (MW) distributions were determined using agarose gel electrophoresis and solid-state nanopore measurements, and HC-HA complex formation was detected via immunoblotting and immunofluorescence. SEC-MALS was used to evaluate TSG-6-mediated HA crosslinking, and synovial fluid and HA solution viscosities were analyzed using multiple particle-tracking microrheology and microfluidic measurements, respectively.ResultsTNF-α concentrations were greater in OA synovial fluid, and TSG6 expression was upregulated in OA synovial membrane and cartilage. TSG-6-mediated HC-HA complex formation was greater in OA synovial fluid and tissues than controls, and HC-HA was localized to both synovial membrane and superficial zone chondrocytes in OA joints. SEC-MALS demonstrated macromolecular aggregation of low MW HA in the presence of TSG-6 and inter-α-inhibitor with concurrent increases in viscosity.ConclusionsSynovial fluid TNF-α concentrations, synovial membrane and cartilage TSG6 gene expression, and HC-HA complex formation were increased in equine OA. Despite the ability of TSG-6 to induce macromolecular aggregation of low MW HA with resultant increases in the viscosity of low MW HA solutions in vitro, HA concentration was the primary determinant of synovial fluid viscosity rather than HA MW or HC-HA crosslinking. The TNF-α-TSG-6-HC-HA pathway may represent a potential therapeutic target in OA.

Investigation of selected parameters of capillary zone electrophoresis method for analysis of isolates of outer membrane vesicles.

The capillary zone electrophoresis (CZE) has recently been proposed by our group as a novel technique for outer membrane vesicles (OMVs) characterization (J. Chromatography 1621 (2020) 461047). In present work the impact of selected parameters of CZE method on OMVs isolates analysis was assessed. It was shown that the extension of sample injection plug length significantly improves the detectability of macromolecular aggregates in CZE. Moreover, a negligible adsorption of OMVs to both uncoated and polymer-modified (poly(DMA-GMA-MAPS)) capillary walls was proven. Finally, the relaxation effect as well as deformation/polarization of vesicles were demonstrated to affect OMVs electrophoretic mobility. The significance of these findings was discussed.

The CNS/PNS Extracellular Matrix Provides Instructive Guidance Cues to Neural Cells and Neuroregulatory Proteins in Neural Development and Repair.

Background. The extracellular matrix of the PNS/CNS is unusual in that it is dominated by glycosaminoglycans, especially hyaluronan, whose space filling and hydrating properties make essential contributions to the functional properties of this tissue. Hyaluronan has a relatively simple structure but its space-filling properties ensure micro-compartments are maintained in the brain ultrastructure, ensuring ionic niches and gradients are maintained for optimal cellular function. Hyaluronan has cell-instructive, anti-inflammatory properties and forms macro-molecular aggregates with the lectican CS-proteoglycans, forming dense protective perineuronal net structures that provide neural and synaptic plasticity and support cognitive learning. Aims. To highlight the central nervous system/peripheral nervous system (CNS/PNS) and its diverse extracellular and cell-associated proteoglycans that have cell-instructive properties regulating neural repair processes and functional recovery through interactions with cell adhesive molecules, receptors and neuroregulatory proteins. Despite a general lack of stabilising fibrillar collagenous and elastic structures in the CNS/PNS, a sophisticated dynamic extracellular matrix is nevertheless important in tissue form and function. Conclusions. This review provides examples of the sophistication of the CNS/PNS extracellular matrix, showing how it maintains homeostasis and regulates neural repair and regeneration.

Aggregative and structural properties of wheat gluten induced by pectin

Pectin is a common food additive used for enhancing the health benefits of dietary fibers, and is the most structurally and functionally complex polysaccharide, rich in galacturonic acid. In this study, we investigated changes in the aggregative property of gluten, their rheological properties, and secondary structure, as well as in the gluten network, when supplemented by apple pectin. Adding pectin was shown to enhance the macromolecular aggregation of gluten, and improved the rheological properties of dough by inducing a dense network of gluten. The presence of pectin decreased α-helix content but increased β-sheet and β-turn structure of gluten, suggesting that pectin affected the hydration level of gluten, leading to the formation of aggregated β-structures. This study provides a better understanding of pectin functionality in wheat flour dough, and is valuable for guiding in the application of pectin in wheat flour food products.

Improving freeze–thaw stability of soy protein isolate-glucosamine emulsion by transglutaminase glycosylation

This paper studies the improvement of freeze–thaw stability of emulsions by incorporating glucosamine into soy protein isolate (SPI) by using transglutaminase. The occurrence of enzymatic glycosylated SPI reaction is confirmed by SDS-PAGE. Through the measurement of creaming index and oiling off, we find that both soy protein isolate-enzymatic without glucosamine (SPI-E) and glycosylated SPI by transglutaminase (SPI-G) can effectively improve the freeze–thaw stability of emulsions. The analysis of particle size, degree of flocculation and coalescence indicates that macromolecular aggregates were formed because transglutaminase enzyme promoted glycosylation and also promoted the cross-linking of protein and protein or the internal cross-linking of protein. Therefore, the particle size of the SPI-G emulsion before freezing and thawing is larger than that of the SPI emulsion. After freeze–thaw cycles, it can be seen that although the particle size of SPI-G is increasing, it is significantly smaller than that of SPI emulsion after freeze–thaw. According to the optical microscope, it can be seen that the SPI emulsion has obvious aggregation of oil droplets after freeze–thawing, and SPI-G effectively improves oil droplet aggregation.

Targeting Lysosomal Degradation Pathways: New Strategies and Techniques for Drug Discovery.

A series of tools for targeted protein degradation are inspiring scientists to develop new drugs with advantages over traditional small-molecule drugs. Among these tools, proteolysis-targeting chimeras (PROTACs) are most representative of the technology based on proteasomes. However, the proteasome has little degradation effect on certain macromolecular proteins or aggregates, extracellular proteins, and organelles, which limits the application of PROTACs. Additionally, lysosomes play an important role in protein degradation. Therefore, lysosome-induced protein degradation drugs can directly regulate protein levels in vivo, achieve the goal of treating diseases, and provide new strategies for drug discovery. Lysosome-based degradation technology has the potential for clinical translation. In this review, strategies targeting lysosomal pathways and lysosome-based degradation techniques are summarized. In addition, lysosome-based degrading drugs are described, and the advantages and challenges are listed. Our efforts will certainly promote the design, discovery, and clinical application of drugs associated with this technology.

Effect of grape seed power on the structural and physicochemical properties of wheat gluten in noodle preparation system

Noodles were prepared using wheat flour supplemented with 1%, 3%, and 5% grape seed power (GSP). The farinograph properties of wheat flour, the textural properties of the dough, and thermal properties of the gluten were determined. The microstructure was analyzed by scanning electron and atomic force microscopy, and the effects of the addition of GSP on the physicochemical and structural properties (free sulfhydryl content, surface hydrophobic region, and secondary structure) of wheat gluten protein were analyzed. 1% GSP promoted the aggregation of gluten proteins by promoting hydrophobic interactions and hydrogen bonding, thus enhanced the noodle quality. Whereas, 3% and 5% GSP addition disrupted the disulfide bonds between gluten protein molecules and formed macromolecular aggregates linked to gluten proteins through non-covalent bonds and hydrophobic interactions, which prevented the formation of the gluten protein reticulation structure. Our study emphasized the interaction between wheat proteins and GSP in noodle making dough.

Fluorescence correlation spectroscopy to unravel the interactions between macromolecules in wine

In this work, the interaction of wine macromolecules with a bovine serum albumin (BSA) was investigated using fluorescence correlation spectroscopy (FCS). FCS offers the opportunity to study molecular and macromolecular aggregation without disturbing the wine by introducing only very small amounts of fluorescently labelled molecules to the system. It was observed that the diffusion coefficient of fluorescently labelled BSA varies with the addition of wine macromolecules, indicating changes in the protein conformation and the formation of complexes and aggregates. The addition of a wine polysaccharide rhamnogalacturonan II-enriched fraction led to aggregation, while addition of a mannoprotein-enriched fraction exhibited a protective effect on protein aggregation. Proteins strongly interacted with tannins, leading to the precipitation of protein-tannin complexes, while the presence of polysaccharides prevented this precipitation. Finally, the application of FCS was demonstrated in real wines, to investigate the problem of protein haze formation through live monitoring of heat-induced aggregation in wine.

Comparison of carrying mechanism between three fat-soluble vitamins and alpha-lactalbumin: Effects on structure and physicochemical properties of alpha-lactalbumin

This study aims to explore the interaction mechanisms between alpha-lactalbumin (ALa) and three fat-soluble vitamins (VA, VD3 and VE) at pH 7.0 and their impacts on structure and functionality of ALa. Analysis of fluorescence spectroscopy showed that vitamins quenched intrinsic fluorescence of ALa in a static mode and cholecalciferol (VD3) had a higher binding affinity for ALa than Retinol (VA) and alpha-tocopherol (VE). Synchronous fluorescence and three-dimensional fluorescence spectra demonstrated the conformation changes of ALa. Meanwhile, fourier transform infrared spectroscopy manifested that three vitamins induced a transition from α-helix to β-sheet in ALa, and VD3 notably increased its random coil content. Furthermore, a combination of VE with ALa generated macromolecular aggregates, based on particle size results. The addition of VA and VD3 increased zeta potential and surface hydrophobicity of ALa, while VE triggered that of ALa initially increased and then decreased with vitamins ranging from 0 to 0.35 mmol/L. Additionally, molecular simulation suggested that VA and VE had a same binding site in the cleft of ALa, but VD3 bound in a hydrophobic pocket in protein, and their binding driving forces were hydrophobic interaction and hydrogen bond. This study reveals that ALa might be a potentially suitable carrier for delivering vitamins, providing a theoretical basis of interaction between proteins and small molecules.

Morphology of chemically in situ precipitated films of polyaniline on the substrate of cellulose triacetate

Thin films of polyaniline were obtained by chemical oxidation of0,05 Maniline with ammonium peroxydisulfate on the substrate of cellulose triacetate in situ in an aqueous solution of0.5 Mcitric acid (CA).These films on flexible substrate of cellulose triacetate were characterized by UV/VIS, FTIR ATR spectroscopy as well as SEM and atomic force microscopy. With the assistance of scanning electron microscope (SEM) was found that the film of polyaniline on substrate of cellulose triacetate, formed predominantly of macromolecular aggregates of different sizes, which are mainly close in the shape to circle. Detailed analysis of 2D-images of atomic force microscope confirmed, that polyaniline aggregates are preferably in the shape to circle. However, analysis of 3D-images displayed that the aggregates obtained by polyaniline on the surface of cellulose triacetate have an irregular quasi cone-shaped appearance with smooth (polished) sides. Obviously, that the growth of these aggregates occurs from the surface into the solution and when the aniline is consumed, happens smoothing effect of surfaces of these formations. In the films of polyaniline were detected the large cone-shaped localized aggregates of macromolecules of polyaniline. The parameters of thin polyaniline films such as: roughness, root mean square, asymmetry, eccentricity, average maximum height of sample as well as average maximum height and depth of roughness were determined and calculated by atomic force microscopy. As we can see from comparison of the calculated results of determining the thickness of polyaniline film on the matrix substrate with different methods shows their good convergence. The established effective thickness by various methods of polyaniline film is 80 nm. Keywords : polyaniline, cellulose triacetate, films, structure, topology, morphology

Effects of Microphase Separation and Density–Density Correlations in Amorphous Polymer Films

The topology of density fluctuations on the surfaces of amorphous thin films prepared from solutions of some flexible-chain polymers has been studied based on electron microscopy data on submicron and micron scales. It is shown that the microphase-separation effects in the films become stronger with an increase in the initial solution concentrations due to self-organization of macromolecular aggregates (clusters): anisotropy, long-range order, and correlation length ξ of density fluctuations increase. The self-organization is completed with formation of an infinite cluster of particles with a periodically inhomogeneous density, which occupies ~30% of the film surface. The density–density correlation function of this cluster on the ~ξ scale is universal and independent of the polymer composition and molecular weight.

Loss of endocytosis-associated RabGEF1 causes aberrant morphogenesis and altered autophagy in photoreceptors leading to retinal degeneration.

Rab-GTPases and associated effectors mediate cargo transport through the endomembrane system of eukaryotic cells, regulating key processes such as membrane turnover, signal transduction, protein recycling and degradation. Using developmental transcriptome data, we identified Rabgef1 (encoding the protein RabGEF1 or Rabex-5) as the only gene associated with Rab GTPases that exhibited strong concordance with retinal photoreceptor differentiation. Loss of Rabgef1 in mice (Rabgef1-/-) resulted in defects specifically of photoreceptor morphology and almost complete loss of both rod and cone function as early as eye opening; however, aberrant outer segment formation could only partly account for visual function deficits. RabGEF1 protein in retinal photoreceptors interacts with Rabaptin-5, and RabGEF1 absence leads to reduction of early endosomes consistent with studies in other mammalian cells and tissues. Electron microscopy analyses reveal abnormal accumulation of macromolecular aggregates in autophagosome-like vacuoles and enhanced immunostaining for LC3A/B and p62 in Rabgef1-/- photoreceptors, consistent with compromised autophagy. Transcriptome analysis of the developing Rabgef1-/- retina reveals altered expression of 2469 genes related to multiple pathways including phototransduction, mitochondria, oxidative stress and endocytosis, suggesting an early trajectory of photoreceptor cell death. Our results implicate an essential role of the RabGEF1-modulated endocytic and autophagic pathways in photoreceptor differentiation and homeostasis. We propose that RabGEF1 and associated components are potential candidates for syndromic traits that include a retinopathy phenotype.

A major ice component in Pluto’s haze

Pluto, Titan and Triton all have low-temperature environments with an N2, CH4 and CO atmospheric composition in which solar radiation drives an intense organic photochemistry. Titan is rich in atmospheric hazes, and Cassini–Huygens observations showed that their formation is initiated with the production of large molecules through ion-neutral reactions. New Horizons revealed that optical hazes are also ubiquitous in Pluto’s atmosphere, and it is thought that similar haze formation pathways are active in this atmosphere as well. However, we show here that Pluto’s hazes may contain a major organic ice component (dominated by C4H2 ice) from the direct condensation of the primary photochemical products in this atmosphere. This contribution may imply that haze has a less important role in controlling Pluto’s atmospheric thermal balance compared to Titan. Moreover, we expect that the haze composition of Triton is dominated by C2H4 ice. Pluto’s haze could have a major icy component created by the condensation of organic molecules such as C4H2. This is different from Titan whose haze, despite a similar atmospheric composition, is mostly macromolecular aggregates. Triton’s haze, instead, should be dominated by ices, particularly C2H4.

Physical mechanisms of amyloid nucleation on fluid membranes

Biological membranes can dramatically accelerate the aggregation of normally soluble protein molecules into amyloid fibrils and alter the fibril morphologies, yet the molecular mechanisms through which this accelerated nucleation takes place are not yet understood. Here, we develop a coarse-grained model to systematically explore the effect that the structural properties of the lipid membrane and the nature of protein-membrane interactions have on the nucleation rates of amyloid fibrils. We identify two physically distinct nucleation pathways-protein-rich and lipid-rich-and quantify how the membrane fluidity and protein-membrane affinity control the relative importance of those molecular pathways. We find that the membrane's susceptibility to reshaping and being incorporated into the fibrillar aggregates is a key determinant of its ability to promote protein aggregation. We then characterize the rates and the free-energy profile associated with this heterogeneous nucleation process, in which the surface itself participates in the aggregate structure. Finally, we compare quantitatively our data to experiments on membrane-catalyzed amyloid aggregation of α-synuclein, a protein implicated in Parkinson's disease that predominately nucleates on membranes. More generally, our results provide a framework for understanding macromolecular aggregation on lipid membranes in a broad biological and biotechnological context.

Low Ice Adhesion Surfaces Based on Flexible Fluorinated Polymers with a Polynorbornene Backbone.

Realizing icephobic surfaces with low ice adhesion and durability continues to be fascinating as well as challenging. Herein, a norbornene-based fluorinated polymer (NFP) with high flexibility and high tensile strength is designed and fabricated using a fluorinated side chain and a norbornene backbone, displaying low ice shear strength less than 20 kPa and excellent durability. Experimental and theoretical analyses show that the flexibility of the polymer chains and the synergistic macromolecular aggregation of the fluorinated side groups and the norbornene backbone play key roles in the excellent surface icephobic properties of the NFP films. Moreover, we also develop a facile approach to the design of durable icephobic slippery surfaces, which possess remarkable icephobic performance. This study not only sheds light on the relationship between the polymer molecular structure and surface icephobic properties but also provides a new avenue to conveniently realize anti-icing coatings.

Effect of regioregularity and role of heteroatom on the chiral behavior of oligo(heteroalkyl thiophene)s.

Novel optically active oligothiophenes bearing electron-donating chiral side chains have been prepared by synthetic methods suitable to achieve regioregular head-to-tail and head-to-head/tail-to-tail derivatives. In particular, the chiral (S)-(2-methyl)butyl moiety was linked at position 3 of the thiophene ring through heteroatoms, such as S or O, to evaluate its effect on the macro molecular aggregation and, consequently, on the chiroptical properties of the material in the solid state. The materials have been fully characterized and investigated by optical and chiroptical methods upon aggregation both from the solution and as cast films. Compared with the related head-to-tail and head-to-head/tail-to-tail poly(3-alkyl)thiophene derivatives, with the same optically active moiety directly linked to the ring and possessing a higher polymerization degree, the chiroptical properties of the newly synthesized oligomers were significant, or even better, and provided insight into the role of intrachain-interchain interactions between the heteroatom and the thienyl sulfur atom.

Structural basis for high-pressure improvement in depolymerization of interfacial protein from RFRS meat batters in relation to their solubility

High-pressure processing (HPP) can modify the construction of interfacial proteins (IPs) to improve the properties of reduced-fat and reduced-salt (RFRS) meat batters. In this study, the relationship between the construction of IPs and their solubility at fat droplet/water interface in RFRS meat batters with HPP treatments was investigated. When 200 MPa for 2 min was applied, the IPs exhibited the highest solubility due to a high concentration of absorbed myosin with the content of random coil 65.62%, but the particle diameter was in reverse. The microscopy revealed the depolymerization of IPs occurred at low pressure, while macromolecular aggregates were produced as the cross-linking of IPs to some degree at pressure ≥ 200 MPa. This phenomenon was supported by the result of SDS-PAGE and the sulfhydryl of IPs. In conclusion, the HPP induced solubility alteration of IPs was achieved by modifying their construction through adjusting the secondary structures and regulating bond interactions.

Studying Changes in the Electrical Resistance of Elastomers Modified by Carbon Nanotubes during Their Compression, Stretching, and Torsion

Developing “smart” materials with improvement of both structural and functional characteristics is one of the promising areas of materials science. Measuring the electrical resistance of CNT-modified (various mass contents) polymers and, in particular, elastomers when performing several tests (compression, stretching, and torsion) at a constant current is relevant in electrical engineering, mechanical engineering, and the aerospace industry. Changes in the elastomer shape under different types of testing lead to the destruction of macromolecules and the structuring of the material as a whole. Therefore, it is important to study the effect of CNT-based modifying fillers on the elastomer. When compressing, stretching, or twisting the nanomodified elastomer, along with the mutual movement of its macromolecular fragments and aggregates, the modifier particles also move, which generally determines the transport of electrons in the resulting structure and affects the physical and mechanical parameters of the composite material. To conduct studies, elastomers containing different amounts of a CNT-based modifying filler were prepared. To investigate and elucidate the relevant dependences, a measuring system (MS) making it possible to determine the values of electrical resistance of the composite material with different contents of CNTs in the polymer matrix composition exposed to various mechanical loads was constructed. On the basis of the results, it was established that the electrical resistance of the elastomer composites modified with 1.0–2.5 wt % CNTs decreases upon compression from 0 to 100 N, whereas when the compression force ranges from 100 to 350 N, the electrical resistance remains unchanged. When the elastomer composites modified with 2–2.5 wt % CNTs were stretched by 30–40%, the electrical resistance was found to increase from 5 × 103 to 1.9 × 107 Ω.

Structural Transformations in Chemical Modification of the Surface of Polypyromellitimide Films

Electron microscopy data are used to investigate the formation of a submicron layer of a polyamido acid (PAAc) on the surface of polypyromellitimide (PI) film subjected to sequential treatment with aqueous alkali and acid solutions. To analyze the topology of distribution of PAAc macromolecule clusters on the surface of modified PI films, PAAc is decorated with silver chloride nanoparticles. The presence of ordering in the spatial distribution of the ensemble density of decorating nanoparticles is revealed. The degree of order is shown to vary nonmonotonically with the duration of alkaline hydrolysis of PI. This variation is explained by superposition of two processes: the formation of PAAc clusters as a result of a topochemical reaction in the macromolecular PI chains and random cluster-cluster aggregation. The formation of PAAc clusters is centered around periodically alternating microdomains, i.e., dense aggregates of PI molecules. Conditions leading to the formation of the ordered cluster PAAc structure upon modification of PI surface are identified.