A high resolution (1)H magic angle spinning NMR study of a high-M(r) subunit of wheat glutenin

Comprehensive amino acid composition analysis of seed storage proteins of cereals and legumes: identification and understanding of intrinsically disordered and allergenic peptides

The seed storage proteins of cereal and legumes are the primary source of amino acids which are required for sustaining the nitrogen and carbon demands during germination and growth. Humans derive most of their dietary proteins from storage proteins in form of a wide variety of foods, for consumption. The amino acid content of most of these proteins is biased and the need for this biasness is not understood. The high abundance of proline, glutamine, and cysteine in cereals makes the gluten fraction viscoelastic. The cereal proteins have less charge and legume proteins have more charge on them. Their non-polar amino acid distribution has large variations. These characteristics are strongly responsible for the partial and complete unfolding of several domains of the storage proteins. Many of the storage proteins share a highly conserved structural feature within the cupin superfamily spread across all kingdoms of life. The intrinsically disordered viscoelastic proteins help in making dough which is vital for the quality of bread. Unfolded regions harbor more immunogenic sequences and cause food-related allergies and intolerance. We have discussed these properties in terms of comparison of cereal and legume storage protein sequences and allergy. Our study supports the findings that large disordered regions contain allergen-representative peptides. Interestingly, a high number of allergen-representative peptides were cleavable by digestive enzymes. Furthermore, unfolded storage proteins mimic microbial immunogens to induce a memory immune response. Results findings can be used to guide the understanding of immunological characteristics of storage proteins and may assist in treatment decisions for food allergy.Communicated by Ramaswamy H. Sarma.

Gluten proteins: Enzymatic modification, functional and therapeutic properties

Glutens are potential proteins with multifunctional therapeutic effects. Their covalence network structures with and without protease inhibitors are expected to enhance or to serve further properties and further technological points such as increased bioactive surfaces, gelatinization, gelation and pasting properties. The depletion of the allergic peptide sequences of gluten proteins comprising sometimes protease inhibitors are valid via the enzymatic ingestion using proteolytic enzymes that might enhance these functional and technological processes by producing active peptides having osmoregulation and regular glass transitions, surface activity for coating and encapsulation properties. In addition to further therapeutic functions such as immunoregulatory, antithrombin and opioidal activities, particularly in eradicating most of the free radicals, suppressing diabetes Mellitus II complications and inhibiting angiotensin converting enzyme cardiovascular growth diseases.

Influence of epichlorohydrin modification on structure and properties of wheat gliadin films

The present study was to examine influence of epichlorohydrin (ECH) modification on structure and properties of glycerol-plasticized wheat gliadin films casting from ethanol/water (70/30 v/v) solution. The modified films were characterized using proton nuclear magnetic resonance ((1)H NMR), Fourier transformation infrared (FTIR) spectra, dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). Water resistance (moisture absorption MA, water vapor permeability WVP, and weight loss in water WLW), tensile mechanical properties (Young's modulus E, tensile strength sigma(b), and elongation at break epsilon(b)), and thermal decomposition behavior were evaluated in relation to ECH content. Experimental results revealed that ECH modification gave rise to marked reduction in WLW and significant improvements in E and sigma(b), which were accompanied by slight variations in MA, WVP, and thermal decomposition temperature. The improvements of E and sigma(b) were related to the formation of a partially cross-linked protein network even though the modification led to reductions in percentages of the hydrogen bonded NH groups and the beta-sheet structure.

Wheat-Gluten-Based Natural Polymer Nanoparticle Composites

A series of wheat-gluten-based nanocomposites were produced by dispersing Cloisite-30B nanoclay particles into plasticized wheat gluten systems under thermal processing conditions. The exfoliation of the nanoparticles as confirmed by wide-angle X-ray diffraction and transmission electron microscopy has resulted in significant enhancement of the mechanical properties for both deamidated proteins and vital gluten systems under 50% relative humidity (RH). Such strength improvement was also pronounced for wheat gluten (WG) systems under a high humidity condition (RH = 85%). A similar level of further strength enhancement was obtained for the WG systems that had been strengthened by blending with poly(vinyl alcohol) (PVA) and cross-linking with glyoxal. Although the nanoclay modifier, a quaternary ammonium, caused an additional plasticization to the materials, the interactions between the gluten matrix and the nanoparticles were predominant in all of these nanocomposites. A solid-state NMR study indicated that the polymer matrix in all of these nanocomposites displayed a wide distribution of chain mobilities at a molecular level (less than 1 nm). The interactions between the nanoparticles and the natural polymer matrix resulted in motional restriction for all components in the mobile phases including lipid, plasticizers, and plasticized components, although no significant influence from the nanoparticles was obtained in the mobility of the rigid phases (unplasticized components). On a scale of 20-30 nm, the deamidated protein systems tended to be homogeneous. The small domain size of the matrix resulted in modifications of the spin-lattice relaxation of these systems via spin diffusion. The residual starch seemed to remain in a relatively larger domain size in WG systems. The nanoparticles could enhance the miscibility between the starch and the other components in the WG nanocomposite, but such miscibility enhancement did not occur in the WG/PVA blend and the cross-linked system. These polymer matrixes were still heterogeneous on a scale of 20-30 nm.

13C and 1H solid state NMR investigation of hydration effects on gluten dynamics

The effect of hydration on the molecular dynamics of soft wheat gluten was investigated by solid state NMR. For this purpose, we recorded static and MAS 1H spectra and SPE, CP, and other selective 13C spectra under MAS and dipolar decoupling conditions on samples of dry and H(2)O and D(2)O hydrated gluten. Measurements of carbon-proton CP times and several relaxation times (proton T(1), T(1rho) and T(2), and carbon T(1)) were also performed. The combination of these techniques allowed both site-specific and domain-averaged motional information to be obtained in different characteristic frequency ranges. Domains with different structural and dynamic behaviour were identified and the changes induced by hydration on the dynamics of different domains could be monitored. The proton spin diffusion process was exploited to get information on the degree of mixing among different gluten domains. The results are consistent with the "loop and train" model proposed for hydrated gluten.

The identification of plant derived structures in humic materials using three-dimensional NMR spectroscopy

Here we demonstrate the application of 3-D NMR spectroscopy to structural studies of humic substances, the most abundant of organic compounds on earth. The increased spectral dispersion provided by the additional dimension is proven to be highly advantageous in separating the overlapping signals observed in 2-D spectra. Assignments of the major aliphatic structures and selected aromatic moieties are given as examples. We find that in a forest soil fulvic acid the major aliphatic materials are likely derived from leaf cuticles and further demonstrate that lignin signatures can be identified among the aromatic species. Once identified from the 3-D spectra, these structures can be assigned using the partial information available in 2-D, and in some cases, in the 1-D spectra. These signals are demonstrated to be characteristic to given samples of natural organic matter, and the case is made for their use as indicators of terrestrial biomarkers in mixtures of compounds with unknown origins.

Study of wheat high molecular weight 1Dx5 subunit by (13)C and (1)H solid-state NMR. II. Roles of nonrepetitive terminal domains and length of repetitive domain

This work follows a previous article that addressed the role of disulfide bonds in the behavior of the 1Dx5 subunit upon hydration. Here the roles of nonrepetitive terminal domains present and the length of the central repetitive domain in the hydration of 1Dx5 are investigated. This was achieved by comparing the hydration behavior of suitable model samples determined by (13)C- and (1)H-NMR: an alkylated 1Dx5 subunit (alk1Dx5), a recombinant 58-kDa peptide corresponding to the central repetitive domain of 1Dx5 (i.e., lacking the terminal domains), and two synthetic peptides (with 6 and 21 amino acid residues) based on the consensus repeat motifs of the central domain. The (13)C cross-polarization and magic angle spinning (MAS) experiments recorded as a function of hydration gave information about the protein or peptide fractions resisting plasticization. Conversely, (13)C single pulse excitation and (1)H-MAS gave information on the more plasticized segments. The results are consistent with the previous proposal of a hydrated network held by hydrogen-bonded glutamines and possibly hydrophobic interactions. The nonrepetitive terminal domains were found to induce water insolubility and a generally higher network hindrance. Shorter chain lengths were shown to increase plasticization and water solubility. However, at low water contents, the 21-mer peptide was characterized by higher hindrance in the megahertz and kilohertz frequency ranges compared to the longer peptide; and a tendency for a few hydrogen-bonded glutamines and hydrophobic residues to remain relatively hindered was still observed, as for the protein and large peptide. It is suggested that this ability is strongly dependent on the peptide primary structure.

Study of high molecular weight wheat glutenin subunit 1Dx5 by 13C and 1H solid-state NMR spectroscopy. I. Role of covalent crosslinking

This work describes a carbon and proton solid-state NMR study of the hydration of a high molecular weight wheat glutenin subunit, 1Dx5. The effect of the presence of disulfide bonds on the hydration behavior of the subunit is investigated by a comparison of the unalkylated and alkylated forms of the protein. Hydration induces partial plasticization of the protein so that some segments become more mobile than others. The 13C cross-polarization and magic-angle spinning (MAS) spectra of the samples in the dry state and at two hydration levels (approximately 40 and approximately 65% D2O) were used to monitor the protein fraction resisting plasticization (trains). Conversely, 13C single pulse excitation and 1H-MAS experiments were used to gain information on the more plasticized segments (loops). The molecular motion of the two protein dynamic populations was further characterized by 13C T1 and 1H T(1rho), T2, and T1 relaxation times. The results suggest that hydration leads to the formation of a network held by a cooperative action of hydrogen bonded glutamines and some hydrophobic interactions. The looser protein segments are suggested to be glycine- and glutamine-rich segments. The primary structure is therefore expected to significantly determine the proportion of trains and loops in the network. The presence of disulfide bonds was observed to promote easier plasticization of the protein and the formation of a more mobile network, probably involving a higher number of loops and/or larger loops.

2D(13)C-(13)C MAS NMR correlation spectroscopy with mixing by true (1)H spin diffusion reveals long-range intermolecular distance restraints in ultra high magnetic field

An improved 2D (13)C-(13)C CP(3) MAS NMR correlation experiment with mixing by true (1)H spin diffusion is presented. With CP(3), correlations can be detected over a much longer range than with direct (1)H-(13)C or (13)C-(13)C dipolar recoupling. The experiment employs a (1)H spin diffusion mixing period tau(m) sandwiched between two cross-polarization periods. An optimized CP(3) sequence for measuring polarization transfer on a length scale between 0.3 and 1.0 nm using short mixing times of 0.1 ms < tau(m) < 1 ms is presented. For such a short tau(m), cross talk from residual transverse magnetization of the donating nuclear species after a CP can be suppressed by extended phase cycling. The utility of the experiment for genuine structure determination is demonstrated using a self-aggregated Chl a/H(2)O sample. The number of intramolecular cross-peaks increases for longer mixing times and this obscures the intermolecular transfer events. Hence, the experiment will be useful for short mixing times only. For a short tau(m) = 0.1 ms, intermolecular correlations are detected between the ends of phytyl tails and ring carbons of neighboring Chl a molecules in the aggregate. In this way the model for the structure, with stacks of Chl a that are arranged back to back with interdigitating phytyl chains stretched between two bilayers, is validated.