Negative Charge Content Research Articles

Fe oxides simultaneously improve stability of Cd and carbon in paddy soil：The underlying influence at aggregate level

Iron (Fe) oxides have a strong adsorption affinity for Cd and organic carbon (SOC). However, under alternate wet-dry (IF) condition,the influences of Fe oxides on the speciation and disrtribution of Cd and SOC in soil aggregates are unkown. In the present study, soils untreated (S), removed (S-Fe) or added (S+Fe) Fe oxide soils were blended with cadmium chloride solution and cultivated for 56 days under different moisture management practices. Compared with the S-Fe soil, the IF treatment increased the contents of Fe oxide-bound SOC (Fe-OC) and Fe/Mn oxide-bound Cd (Fe/Mn-Cd) by 18.5–29.8-fold and 1.45–2.45-fold, repectively, in the S and S+Fe soils, corresponding to a 36 %−42 % increase in the recalcitrant C pool (RCP) and a 53 %−87 % decrease in the exchangeable Cd content. These results could be attributed to soil particle aggregation and Fe redistribution. Fe addition promoted the transfer of Cd/SOC accumulated in microaggregates to macroaggregates and increased the variable negative charge content in macroaggregates and the adsorption capacity of macroaggregates for Cd/SOC. More Cd/SOC accumulated in macroaggregates in Fe oxide-bound form, which reduced the risk of Cd migration and Cd availability and increased the physical protection of SOC. Therefore, Fe oxide has great potential to simultaneously reduce carbon emissions and cadmium toxicity in paddy soil.

Star Polymer Size, Charge Content, and Hydrophobicity Affect their Leaf Uptake and Translocation in Plants.

Determination of how the properties of nanocarriers of agrochemicals affect their uptake and translocation in plants would enable more efficient agent delivery. Here, we synthesized star polymer nanocarriers poly(acrylic acid)-block-poly(2-(methylsulfinyl)ethyl acrylate) (PAA-b-PMSEA) and poly(acrylic acid)-block-poly((2-(methylsulfinyl)ethyl acrylate)-co-(2-(methylthio)ethyl acrylate)) (PAA-b-P(MSEA-co-MTEA)) with well-controlled sizes (from 6 to 35 nm), negative charge content (from 17% to 83% PAA), and hydrophobicity and quantified their leaf uptake, phloem loading, and distribution in tomato (Solanum lycopersicum) plants 3 days after foliar application of 20 μL of a 1g L-1 star polymer solution. In spite of their property differences, ∼30% of the applied star polymers translocated to other plant organs, higher than uptake of conventional foliar applied agrochemicals (<5%). The property differences affected their distribution in the plant. The ∼6 nm star polymers exhibited 3 times higher transport to younger leaves than larger ones, while the ∼35 nm star polymer had over 2 times higher transport to roots than smaller ones, suggesting small star polymers favor symplastic unloading in young leaves, while larger polymers favor apoplastic unloading in roots. For the same sized star polymer, a smaller negative charge content (yielding ζ ∼ -12 mV) enhanced translocation to young leaves and roots, whereas a larger negative charge (ζ < -26 mV) had lower mobility. Hydrophobicity only affected leaf uptake pathways, but not translocation. This study can help design agrochemical nanocarriers for efficient foliar uptake and targeting to desired plant organs, which may decrease agrochemical use and environmental impacts of agriculture.

Ethanol induced the gelation behavior of duck egg whites

In this study, changes in the gel properties, microstructure, and molecular interaction force during the formation of duck egg white (EW) gel induced by ethanol were investigated. Results showed that the viscosity of the EW increased with increasing ethanol concentration and treatment time. The hardness and cohesiveness of the formed gel increased first with prolonged treatment time, then decreased slightly, and finally almost kept stable. The increase in the centrifugal water holding capacity and transformation of immobile and free water into bound water was related to the increasingly compact structure of the gel network. The force that maintained the gel network was mainly ionic bond (~45%) and disulfide bonds (~45%). The hydrogen bond and hydrophobic interaction were extremely low. SDS-PAGE results showed that the ethanol-treated EW proteins were degraded to some extent, but the bands did not significantly change with time. The negative charge content and surface hydrophobicity of the protein increased continuously. The secondary structure of the EW gel showed that the mutual transformation of β-sheet, random coil, α-helix, and β-turn resulted in the good texture characteristics of the gel. The ethanol treatment promoted the disulfide bond cross-linking of the duck EW proteins, and the network structure of the EW gel became increasingly compact, resulting in a series of changes in the water retention and binding water content of the gel. Protein aggregation also occurred, which enhanced the hardness, springiness, and cohesiveness of the duck EW gel.

The Nature's Superviscous Nano-channel: Insight from Big Data-Driven Biophysical Modeling

The nuclear pore complex (NPC) is the unique gateway to the cell nucleus and is primarily filled with intrinsically disordered proteins (IDPs) rich in Phe-Gly (FG) repeat domains. While the microdynamics of these IDPs is still under debate, there is no information and/or consensus about their microrheological properties. Here, we use state-of-the-art computational methods to explore, for the first time, the microrheology of IDPs confined inside the nuclear pore. Our results indicate that the IDPs rich in FG repeat domains show an intriguing rheological behavior, which uniquely stems from the interplay of biophysical factors including hydrophobicity, charge, the ratios of positive and negative charge content to hydrophobicity content, geometrical confinement, chains’ lengths, channel wall permeability, and the chains’ end-tethering. Performing several long-run biophysical simulations of tens of milliseconds, we developed detailed mechanical spectrums of the polymeric meshwork inside the NPC under these physical conditions over a wide range of frequencies. It appears that among these factors, the chains’ end-tethering plays the dominant role in shaping the mechanical spectrum of FG-meshwork, particularly in the low-frequency regime. The frequency-dependent viscosity of the FG-meshwork is reminiscent of pseudo-plasticity, and thus, the FG-repeats form a shear-thinning polymeric meshwork. The meshwork poses a ‘super-viscous’ environment to the inert (non-specific) cargos while behaving as a less viscous liquid for nuclear-transport-factor-bound cargos.

N-terminal Acetylation Stabilizes N-terminal Helicity in Lipid- and Micelle-bound α-Synuclein and Increases Its Affinity for Physiological Membranes

The Parkinson disease protein α-synuclein is N-terminally acetylated, but most in vitro studies have been performed using unacetylated α-synuclein. Binding to lipid membranes is considered key to the still poorly understood function of α-synuclein. We report the effects of N-terminal acetylation on α-synuclein binding to lipid vesicles of different composition and curvature and to micelles composed of the detergents β-octyl-glucoside (BOG) and SDS. In the presence of SDS, N-terminal acetylation results in a slightly increased helicity for the N-terminal ~10 residues of the protein, likely due to the stabilization of N-terminal fraying through the formation of a helix cap motif. In the presence of BOG, a detergent used in previous isolations of helical oligomeric forms of α-synuclein, the N-terminally acetylated protein adopts a novel conformation in which the N-terminal ~30 residues bind the detergent micelle in a partly helical conformation, whereas the remainder of the protein remains unbound and disordered. Binding of α-synuclein to lipid vesicles with high negative charge content is essentially unaffected by N-terminal acetylation irrespective of curvature, but binding to vesicles of lower negative charge content is increased, with stronger binding observed for vesicles with higher curvature. Thus, the naturally occurring N-terminally acetylated form of α-synuclein exhibits stabilized helicity at its N terminus and increased affinity for lipid vesicles similar to synaptic vesicles, a binding target of the protein in vivo. Furthermore, the novel BOG-bound state of N-terminally acetylated α-synuclein may serve as a model of partly helical membrane-bound intermediates with a role in α-synuclein function and dysfunction.

Simulating POPC and POPC/POPG Bilayers: Conserved Packing and Altered Surface Reactivity.

Molecular dynamics (MD) simulation is a popular technique to study bilayer structural properties, but it has not been widely used in mixed bilayers of neutral and charged lipids. Here, we present results from constant temperature and pressure MD simulations of a 2-oleoyl-1-pamlitoyl-sn-glyecro-3-phosphocholine (POPC) bilayer containing 23% 2-oleoyl-1-pamlitoyl-sn-glyecro-3-glycerol (POPG). The simulations were performed using the recently updated CHARMM force field and involved two bilayers of 104 and 416 lipids. A control simulation of a pure POPC bilayer of 128 lipids yielded equilibrium structural properties that compare very well with experimental data. The average equilibrium properties of the mixed bilayer systems were very similar to those of the pure POPC. However, nearly one-half of all the POPG lipids were found to be involved in hydrogen bonding with POPC lipids. Furthermore, the hydration of the mixed bilayer is different from that of the pure POPC, with the former inducing ordering of water molecules at longer distances. Thus, a phospholipid bilayer with ∼23% negative charge content in the liquid crystalline phase differs from its neutral counterpart only at the headgroup.

Spatial Structure and Composition of Polysaccharide−Protein Complexes from Small Angle Neutron Scattering

We use small angle neutron scattering (SANS), with an original analysis method, to obtain both the characteristic sizes and the inner composition of lysozyme-pectin complexes depending on the charge density. Lysozyme is a globular protein and pectin a natural anionic semiflexible polysaccharide with a degree of methylation (DM) 0, 43, and 74. For our experimental conditions (buffer ionic strength I = 2.5 10(-2) mol/L and pH between 3 and 7), the electrostatic charge of lysozyme is always positive (from 8 to 17, depending on pH). The pectin charge per elementary chain segment is negative and can be varied from almost zero to one through the change of DM and pH. The weight molar ratio of lysozyme on pectin monomers is kept constant. The ratio of negative charge content per volume to positive charge content per volume, -/+, is varied between 10 and 0.007. On a local scale, for all charged pectins, a correlation peak appears at 0.2 A(-1) due to proteins clustering inside the complexes. On a large scale, the complexes appear as formed of spherical globules with a well-defined radius of 10 to 50 nm, containing a few thousands proteins. The volume fraction Phi of organic matter within the globules derived from SANS absolute cross sections is around 0.1. The protein stacking, which occurs inside the globules, is enhanced when pectin is more charged, due to pH or DM. The linear charge density of the pectin determines the size of the globules for pectin chains of comparable molecular weights whether it is controlled by the pH or the DM. The radius of the globules varies between 10 and 50 nm. In conclusion, the structure is driven by electrostatic interactions and not by hydrophobic interactions. The molecular weight also has a large influence on the structure of the complexes because long chains tend to form larger globules. This may be one reason why DM and pH are not completely equivalent in our system, because DM0 has a short mass, but this may not be the only one. For very low pectin charge (-/+ = 0.07), globules do not appear and the scattering signals a gel-like structure. We did not observe any beads-on-a-string structure.

Mitochondrial creatine kinase interaction with heterogeneous monolayers: Effect on lipid lateral organization

Our study highlights the tight relationship between protein binding to monolayers and the phase-state of the phospholipids. Interaction of mitochondrial creatine kinase with phospholipidic membranes was analysed using a two-phase monolayer system containing anionic phospholipids under chain mismatch conditions. Monolayers were made up of mixtures of DMPC/DPPG or DPPC/DMPG containing 40% negatively charged phospholipids which is approximately the negative charge content of the mitochondrial inner membrane. Langmuir isotherms of these monolayers showed that they underwent a phase transition from a liquid expanded state to a liquid-condensed phase at about 2 mN/m and 5 mN/m respectively. Interface morphology modifications caused by injection of mtCK under these monolayers at low or high surface pressure were monitored by Brewster angle microscopy. This work provides evidence that the presence at the air/water interface of discrete domains with increased charge density, may lead to difference in partition of soluble proteins such as mtCK, interacting with the lipid monolayer. Conversely these proteins may help to organize charged phospholipid domains in a membrane.

Arabino-Galactan Proteins from Pistacia lentiscus var. chia: isolation, characterization and biological function

Arabino-Galactan Proteins (AGPs) were isolated from Chios mastic gum (CMG) by using a buffer containing 0.1 M NaCl, 20 mM Tris-HCl, pH 7.5. Protein analytical methods, combined with specific procedures for carbohydrate characterization, indicated the presence of highly glycosylated protein backbone. In particular, staining by Yariv reagent of the electrophoretically separated molecules revealed the existence of arabinose and galactose and such a modification is characteristic for AGPs. After experiments involving extensive dialysis of the isolated extracts against water and atomic absorption, there was evidence of the existence of zinc ions that are probably covalently bound to the AGPs. By using anion-exchange chromatography, capillary electrophoresis, colorimetric methods and GC-MS, it was found that the extracts were separated into three major populations (A, B, and C), which were consistent with their respective negative charge content namely, uronic acid. The characterization of neutral sugars that was investigated with GC-MS showed the existence of arabinose and galactose in different amounts for each group. Experiments concerning the inhibition of growth of Helicobacter pylori in the presence of AGPs, as is shown for other CMG constituents, showed that the extracts of at least 1.4 g CMG affected the viability of the bacterium. There is no evidence as to whether the AGPs provoke abnormal morphologies of H. pylori, as is reported for the total CMG, or for O-glycans that possess terminal alpha1, 4-linked N-acetylglucosamine and are expressed in the human gastric mucosa; this has to be further investigated.

Hidrólise seletiva de carboxiamidas de resíduos de asparagina e glutamina em colágeno: preparação e caracterização de matrizes aniônicas para uso como biomateriais

This work describes the selective hydrolysis of carboxyamide groups of asparagine and glutamine of collagen matrices for the preparation of negatively charged collagen biomaterials. The reaction was performed in the presence of chloride and sulfate salts of alkaline and alkaline earth metals in aqueous dimethylsulfoxide solution and, selectively hydrolysis of carboxyamide groups of collagen matrices was promoted without cleavage of the peptide bond. The result is a new collagen material with controlled increase in negative charge content. Although triple helix secondary structure of tropocollagen was preserved, significative changes in thermal stabilities were observed in association with a new pattern of tropocollagen macromolecular association, particularly in respect microfibril assembly, thus providing at physiological pH a new type of collagen structure for biomaterial preparation, characterized by different charge and structural contents .

The measurement of negative charge content in cartilage using a colloid titration technique

A colloid titration technique has been used to determine the sulfate and carboxylate content of various glycosaminoglycans and has been validated by comparing the results with data obtained using well-established techniques. The method has been applied to the measurement of the negative charge content of cartilage slices at various depths from the articular surface and to the determination of sulfate and carboxylate contents in bovine nasal septa. Titrations of nasal septa were performed on milled cartilage, on cartilage digested with papain and on proteoglycans purified by cesium chloride gradient centrifugation of guanidinium chloride extracts. The sulfate content was similar for all three preparations (0.5 μeq per milligram dry cartilage). However, the carboxylate content determined on milled cartilage was 40% higher than that obtained for cartilage digested with papain or for purified proteoglycans; this implies the possible contribution of carboxyl groups from structural glycoproteins present in the extracellular matrix. The carboxylate content determined on purified proteoglycans was in excellent agreement with values calculated from chemical analyses.

Microspectrophotometric quantitation of glycosaminoglycans in articular cartilage sections stained with Safranin O.

A new microspectrophotometric method was developed for quantitation of glycosaminoglycans with Safranin O dye in articular cartilage matrix. From histological sections molar extinction coefficient of Safranin O was determined and used to measure the dye content of the sections. The amount of glycosaminoglycans was determined with depth of bovine articular cartilage by both gas chromatography and thin layer chromatography to calculate the fixed negative charge content. Comparison between the results revealed that binding of Safranin O to glycosaminoglycan polyanions was stoichiometric and showed minimal nonspecific staining. The method provides an accurate technique for quantitation and localization of fixed negative charge content of glycosaminoglycans in the articular cartilage matrix. Specific enzyme digestions enable detection of separate glycosaminoglycans.