Size and shape of the repetitive domain of high molecular weight wheat gluten proteins. I. Small-angle neutron scattering

Biomass Separators as a "Lifesaver" for Safe and Long-Life Lithium Metal Batteries

The growth of lithium dendrites and the shuttle of polysulfides in lithium metal batteries (LMBs) have hindered their development. In LMBs, the cathode and anode are separated by a separator, although this does not solve the battery's issues. The use of biomass materials is widespread for modifying the separator due to their porous structure and abundant functional groups. LMBs perform more electrochemically when lithium ions are deposited uniformly and polysulfide shuttling is reduced using biomass separators. In this review, we analyze the growth of lithium dendrite and the shuttle of polysulfide in LMBs, summarize the types of biomass separator materials and the mechanisms of action (providing mechanical barriers, promoting uniform deposition of metal ions, capturing polysulfides, shielding polysulfide). The prospect of developing new separator materials from the perspective of regulating ion transport and physical sieving efficiency as well as the application of advanced technologies such as synchrotron radiation to characterize the mechanism of action of biomass separators is also proposed.

Dissecting the Disulfide Linkage of the N-Terminal Domain of HMW 1Dx5 and Its Contributions to Dough Functionality

The N-terminal domain of HMW-GS 1Dx5 (1Dx5-N) contains three cysteine residues (Cys10, Cys25, Cys40), which are the basis of gluten network formation through disulfide bonds. Disulfide linkage in 1Dx5-N was dissected by site-directed mutagenesis and LC-MS/MS, and its contributions to structural and conformational stability of 1Dx5-N and dough functionality were investigated by circular dichroism, intrinsic fluorescence, surface hydrophobicity determination, size exclusion chromatography, nonreducing/reducing SDS-PAGE, atomic force microscopy, and farinographic analysis. Results showed that Cys10 and Cys40 of 1Dx5-N were the active sites for intermolecular linkage. Meanwhile, Cys40 also exhibited the ability to form intrachain disulfide linkage with Cys25. Moreover, Cys10 and Cys40 played a functionally important role in maintaining the structural and conformational stability and high surface hydrophobicity of the N-terminal domain of HMW-GS, which in turn facilitated the formation of HMW polymers and massive disulfide linkage of HMW-GS through hydrophobic interaction. Additionally, the 1Dx5-N mutants in which Cys were replaced by serine (Ser) presented different effects on dough functionality, while only the C25S mutant produced positive effects compared with wild type 1Dx5-N. Na₂CO₃-induced β-elimination of cystine might occur in glutenin without heating, which would make it much easier to reduce the nutritional quality of flour products by the cost of lysine. Therefore, these results give a deep understanding of the disulfide linkage of the N-terminal domain of HMW-GS and its functional importance, which will provide a practical guide to effectively generate a superior HMW-GS allele by artificial mutagenesis.

The soluble recombinant N-terminal domain of HMW 1Dx5 and its aggregation behavior

This study seeks to clarify and determine the fundamental properties of N-terminal domain of high molecular weight glutenin subunits (HMW-GS) 1Dx5 (1Dx5-N). 1Dx5-N was expressed in E. coli and its solubility was measured by spectrophotometry. Effects of edible salts (NaCl, Na₂CO₃), disulfide bond reductant dithiothreitol (DTT) and hydrophobic interactions of denaturant sodium dodecyl sulfonate (SDS) on 1Dx5-N polymer were investigated by native polyacrylamide gelelectrophoresis (PAGE), nonreducing/reducing SDS-PAGE, intrinsic fluorescence, size exclusion chromatography (SEC), dynamic light scattering (DLS) and circular dichroism (CD). Results showed that 1Dx5-N formed a soluble aggregate in aqueous solutions by native-PAGE, clarifying the role of N-terminal of HMW-GS in the insolubility of the whole subunits. Meanwhile, the hydrophobic interaction was more potent in promoting the aggregation of 1Dx5-N in aqueous solutions from the results of SEC, DLS and CD. Edible salts, NaCl and Na₂CO₃, could improve the polymer formation of 1Dx5-N through disulfide bonds. Moreover, Na₂CO₃ at high concentrations (>200mM) greatly favored polymer formation by disulfide bonds, and it induced other types of cross-links between amino acids in 1Dx5-N according to nonreducing/reducing SDS-PAGE and fluorescence spectrum. Moreover, the formation of covalent bonds was reinforced by hydrophobic interactions between 1Dx5-N. Therefore, these results provide much novel information on the N-terminal domain of HMW-GS to facilitate the understanding of its functional properties in wheat flour.

Shape Persistence of Polyproline II Helical Oligoprolines

Oligoprolines are commonly used as molecular scaffolds. Past studies on the persistence length of their secondary structure, the polyproline II (PPII) helix, and on the fraction of backbone cis amide bonds have provided conflicting results. We resolved this debate by studying a series of spin-labeled proline octadecamers with EPR spectroscopy. Distance distributions between an N-terminal Gd(III) -DOTA (DOTA=1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) label and a nitroxide label at one of five evenly spaced backbone sites allowed us to discriminate between the flexibility of the PPII helix and the cis amide contributions. An upper limit of 2 % cis amide bonds per residue was found in a 7:3 (v/v) water/glycerol mixture, whereas cis amides were not observed in trifluoroethanol. Extrapolation of Monte Carlo models from the glass transition to ambient temperature predicts a persistence length of ≈3-3.5 nm in both solvents. The method is generally applicable to any type of oligomer for which the persistence length is of interest.

Effect of frozen storage on molecular weight, size distribution and conformation of gluten by SAXS and SEC-MALLS

In this study, the effects of frozen (−18 °C) storage time on molecular weight, size distribution, conformation, free amino groups and free sulfhydryl groups of gluten were studied by small-angle X-ray scattering (SAXS), multi-angle laser light scattering (MALLS) in conjunction with a size exclusion chromatography (SEC) and spectrophotometrically. The results showed that the gluten dissolved in 50 mM acetic acid appeared to be similar to quasi-spherical of the chain conformation and the slope of theconformation plot decreased during the storage. Both the molecular weight and radius of gyration of the frozen gluten decreased with the storage time showing a depolymerization in the high molecular weight fraction of gluten (10⁵ Da ~ 10⁹ Da). Therefore, at constant molecular weight the change of the chain conformation did not show a clear correlation with the storage time. The free amino groups content changed little and the free sulfhydryl groups content of the gluten increased from 9.8 μmol/g for the control to 12.87 μmol/g for 120-day-stored gluten, indicating that the water redistribution and ice recrystallization lead to the breakage of the disulphide bonds and may be one of the reasons for the depolymerization of gluten polymer.

Structure and morphology of wheat gluten films: from polymeric protein aggregates toward superstructure arrangements

Evaluation of structure and morphology of extruded wheat gluten (WG) films showed WG protein assemblies elucidated on a range of length scales from nano (4.4 Å and 9 to 10 Å, up to 70 Å) to micro (10 μm). The presence of NaOH in WG films induced a tetragonal structure with unit cell parameters, a = 51.85 Å and c = 40.65 Å, whereas NH(4)OH resulted in a bidimensional hexagonal close-packed (HCP) structure with a lattice parameter of 70 Å. In the WG films with NH(4)OH, a highly polymerized protein pattern with intimately mixed glutenins and gliadins bounded through SH/SS interchange reactions was found. A large content of β-sheet structures was also found in these films, and the film structure was oriented in the extrusion direction. In conclusion, this study highlights complexities of the supramolecular structures and conformations of wheat gluten polymeric proteins in biofilms not previously reported for biobased materials.

Structure of algal-born phenolic polymeric adhesives

Adhesive materials extracted from the brown alga Fucus serratus are composed of phenolic polymer, alginate, and CaCl2. The phenolic polymer undergoes an oxidation reaction in the presence of bromoperoxidase, KI, and H2O2. The nanostructure of the adhesive was investigated using small angle X-ray scattering, light scattering, and cryo- transmission electron microscopy experiments. These have shown that the phenolic polymer undergoes self-assembly and forms flexible chain-like objects. Oxidation or adding alginate does not alter this structure. However, once calcium ions are added, a rigid network is formed. Presumably, this network is responsible for the cohesive strength of the glue.

Incorporating intermicellar interactions in the fitting of SANS data from cationic wormlike micelles

Small-angle neutron scattering (SANS) from cationic wormlike micellar solutions composed of hexadecyltrimethylammonium bromide (CTABr) and hexadecylpyridinium bromide (CPyBr) in deuterated water was studied at 40 degrees C as a function of surfactant and salt concentrations. Two scattering functions of semiflexible chains incorporating excluded volume effects, with and without the intermicellar interactions, were used in SANS data model fitting. Two needed changes were made in the well-accepted models. Extensive and systematic SANS data analysis suggests the robustness of these corrected scattering functions when the intermicellar interactions are included. The influence of the headgroups and ionic strength on the contour length and micellar flexibility of these two systems was demonstrated on the basis of the quantitative structural information obtained from the model fitting. Micellar flexibility was found to depend on surfactant concentration, even when intermicellar interactions were taken into account, despite predictions to the contrary.

Cloning, bacterial expression, purification and structural characterization of N-terminal-repetitive domain of gamma-Gliadin

The gene encoding the repetitive domain located in the N-terminal half of gamma-Gliadin from wheat endosperm has been subcloned into a thioredoxin expression system (pET102/D-Topo). It was over-expressed as fusion protein with thioredoxin in Escherichia coli. Thioredoxin was removed by enterokinase cleavage or by acid cleavage at the respective engineered recognition sites. The soluble N-terminal half of gamma-Gliadin was purified by affinity and reverse-phase chromatography. While, the enterokinase cleavage leaded to only one species detectable by mass spectroscopy, the acid cleavage resulted in a three different length polypeptides, due to the presence of the same number of acid cleavage sites. The secondary structure of the purified protein domain was analysed by circular dichroism, showing an spectral shape common to a Poly(Pro) II conformation. The spectrum is dominated by a large negative peak centred around 201 nm and a broad shoulder centred around 225 nm. Also, the temperature denaturation process was studied. The differences observed in the spectra show two main tendencies, the increment of the shoulder intensity, and the drop of the intensity of the peak around 201. When the sample was cooled down, the change on intensity of the shoulder around 225 was completely reversible and that around the 201 nm peak reached a reversibility of 90%. Such structure and thermal behaviour are characteristic of the repetitive domains of the wheat prolamins.