Wenlung Chen

Chemical composition, physical properties, and antioxidant activities of yam flours as affected by different drying methods

Yams (the tubers of the Dioscorea spp.), consumed and regarded as medicinal food in traditional Chinese herbal medicine, are seasonal foods and easily deteriorate during storage. It is of great importance to prolong the storage of yams for supplying in the off-season and without losing nutritional functionality. Three varieties of yams, Dioscorea alata (cultivars of Tai-Nung no. 2 and Ta-Shan) and D. purpurea (cultivar of Ming-Chien), were made into flours by freeze-drying, hot air-drying, and drum-drying in this report. The proximate compositions and physical properties, as well as antioxidant activities, of yam flours were determined. While drying methods showed significant effects on the moisture contents of yam flours, they had no marked effects on other components of yam flours. Colour attributes and physical properties were all affected by drying methods to different extents. While freeze-drying usually preserved more antioxidant activity of the yam flours, yam flours made of different yam varieties showed different antioxidant mechanisms.

Induction of amyloid fibrils by the C-terminal fragments of TDP-43 in amyotrophic lateral sclerosis.

TAR DNA-binding protein 43 (TDP-43) has been identified as the major ubiquitinated aggregates in the inclusion bodies in the patients of amyotrophic lateral sclerosis (ALS) since 2006 and become a crucial culprit for ALS and related motor neuron diseases. Recent literature has further indicated that the major components of these aggregates are hyper-phosphorylated TDP-43 C-terminus. In an effort to clarify the conformational and physical properties of its disordered C-terminal domain, we have synthesized several peptide fragments and shown that only D1 within D1-4 can form twisted fibrils with a cross section of approximately 11 nm in width under the incubation of phosphate buffer. In contrast, the D2-4 peptides all formed amorphous aggregates, showing different aggregation propensities. In addition to D1, two pathological mutant peptides, A315T and G294A, can also form fibrils that share similar shape and morphology with neuronal cytoplasmic inclusions. We propose that the residues with this region (287-322), which contains myriads of glycine repeats, may contribute significantly to the fiber formation as well as aggregation propensity. Moreover, from the conformational characterizations of D1, A315T, and G294A with EM, CD, fluorescence, and Raman spectroscopy, we found that all three peptides formed an amyloid structure, providing insights into the nature of its aggregation vis a vis the other fragments in the C-terminus of TDP-43.

Dietary vitamin E supplementation affects tissue lipid peroxidation of hybrid tilapia, Oreochromis niloticus x O. aureus

A feeding trial was conducted to evaluate the effects of dietary vitamin E contents on the growth, ascorbate induced iron-catalyzed lipid peroxidation in post-mortem muscle and liver tissue, and Raman spectral changes in lens of juvenile hybrid tilapia (Oreochromis niloticus x O. aureus). Experimental fish were fed practical diets supplemented with 0, 50, 100, 200, 450 and 700 mg alpha-tocopheryl acetate/kg diet for 14 weeks. There was no significant difference in weight gain, feed conversion ratio and protein efficiency ratio among fish fed test diets (P>0.05). Protein content of fish fed diet containing the lowest vitamin E level was the lowest (P<0.05) among all groups. No difference was found in other body constituents among test fish (P>0.05). The thiobarbituric acid-reactive substances produced by iron-catalyzed lipid peroxidation in muscle and liver tissue of fish fed the diet without alpha-tocopheryl acetate supplementation were significantly (P<0.05) greater than those from fish fed diets containing higher levels of alpha-tocopheryl acetate. Dietary vitamin E supplementation increased the antioxidant capability of tilapia tissues against lipid peroxidation. Further, dietary vitamin E supplementation also influenced the lens cortical membrane structure of tilapia.

A simple and direct isolation of whey components from raw milk by gel filtration chromatography and structural characterization by Fourier transform Raman spectroscopy

A simple and economical method to isolate whey protein from fresh raw milk is developed by serial defatting, casein eliminating, lactose removing, and separating by gel filtration chromatography. Four major whey components, including immunoglobulin (Ig), bovine serum albumin (BSA), beta-lactoglobulin (beta-Lg) and alpha-lactalbumin (alpha-Lac), and a non-protein of low molecular mass ( approximately 1.7 kDa) but strong absorbance at 280 nm, are detected simultaneously. The small non-protein molecule is rich in aromatic amino acids and thiol groups as supported by the structural characterization with near infrared Fourier transform Raman spectroscopy (FT-Raman). FT-Raman results show that the secondary structure of Ig is dominated by anti-parallel beta-pleated sheet; BSA is mainly in alpha-helix; both beta-form and unordered structure are important in beta-Lg; while alpha-Lac is mostly in alpha-helix coupling with random coil. Differences in the Raman profile for each whey component reflect their intrinsic compositional differences and distinct spatial arrangement. The S-S linkages diverging around 510-540 cm(-1) indicate that the conformation of disulfide bonds in each whey components is different, which may be responsible for their diversified behaviors in solubility, rheological and functional properties.

Structural Analysis of Triacylglycerols and Edible Oils by Near-Infrared Fourier Transform Raman Spectroscopy

Fourier transform Raman spectroscopy was employed for structural analysis of triacylglycerols and edible oils. Raman spectra sensitively reflected structural changes in oils. Even slight structural fluctuation between triacylglycerols and free fatty acids led to obvious differences in Raman bands as shown by C–O–C stretching from 800 to 1000 cm−1 and the band at 1742 cm−1. Structural difference in geometric isomers was easily distinguished as proved by C = C stretching at 1655 cm−1 (cis) shifting to 1668 cm−1 (trans) and by =C–H in-plane bending at 1266 cm−1 in cis disappearing in the trans isomer. Raman intensity at 1266, 1302, and 1655 cm−1 changed concomitantly with the change of double-bond content in oils. It showed that FT-Raman was capable of precisly reflecting the content of double bonds in oils. A linear correlation with high consistency between the Raman intensity ratio (v1655/v1444) and the iodine value was obtained for commercial oils. Based on the results, FT-Raman spectroscopy proved itself a simple and rapid technique for oil analysis since each measurement could be directly completed in 3 min without any sample modifications.

The influence of pathological mutations and proline substitutions in TDP-43 glycine-rich peptides on its amyloid properties and cellular toxicity.

TAR DNA-binding protein (TDP-43) was identified as the major ubiquitinated component deposited in the inclusion bodies in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U) in 2006. Later on, numerous ALS-related mutations were found in either the glycine or glutamine/asparagine-rich region on the TDP-43 C-terminus, which hinted on the importance of mutations on the disease pathogenesis. However, how the structural conversion was influenced by the mutations and the biological significance of these peptides remains unclear. In this work, various peptides bearing pathogenic or de novo designed mutations were synthesized and displayed their ability to form twisted amyloid fibers, cause liposome leakage, and mediate cellular toxicity as confirmed by transmission electron microscopy (TEM), circular dichroism (CD), Thioflavin T (ThT) assay, Raman spectroscopy, calcein leakage assay, and cell viability assay. We have also shown that replacing glycines with prolines, known to obstruct β-sheet formation, at the different positions in these peptides may influence the amyloidogenesis process and neurotoxicity. In these cases, GGG308PPP mutant was not able to form beta-amyloid, cause liposome leakage, nor jeopardized cell survival, which hinted on the importance of the glycines (308–310) during amyloidogenesis.

Conformational switch of polyglutamine-expanded huntingtin into benign aggregates leads to neuroprotective effect

The abundant accumulation of inclusion bodies containing polyglutamine-expanded mutant huntingtin (mHTT) aggregates is considered as the key pathological event in Huntington’s disease (HD). Here, we demonstrate that FKBP12, an isomerase that exhibits reduced expression in HD, decreases the amyloidogenicity of mHTT, interrupts its oligomerization process, and structurally promotes the formation of amorphous deposits. By combining fluorescence-activated cell sorting with multiple biophysical techniques, we confirm that FKBP12 reduces the amyloid property of these ultrastructural-distinct mHTT aggregates within cells. Moreover, the neuroprotective effect of FKBP12 is demonstrated in both cellular and nematode models. Finally, we show that FKBP12 also inhibit the fibrillization process of other disease-related and aggregation-prone peptides. Our results suggest a novel function of FKBP12 in ameliorating the proteotoxicity in mHTT, which may shed light on unraveling the roles of FKBP12 in different neurodegenerative diseases and developing possible therapeutic strategies.

Structural characterization of dioscorin, the major tuber protein of yams, by near infrared Raman spectroscopy

As very little is known about the molecular structure of dioscorin, the major storage protein of yam tuber, we report here FT-Raman spectroscopic investigation of this yam protein isolated from D. alata L., for the first time. According to a series of purification and identification by ion-exchange chromatography, gel chromatography, SDS-PAGE, and MALDI-TOF-MS, it shows that the major storage protein is made up of dioscorin A (M.W. ~33 kDa) and dioscorin B (M.W. ~31 kDa). Raman spectral results indicate that the secondary structure of dioscorin A is major in α-helix, while dioscorin B belongs to anti-parallel β- sheet. It also shows that the microenvironment of major amino acids including tyrosine, phenylalanine, tryptophan, and methionine, and cysteine exhibit explicit differences between these two components. The conformation of disulfide bonding in dioscorin A predominates in Gauche-Gauche-Trans form, while Gauche-Gauche-Gauche and Trans-Gauche-Trans share the conformation in dioscorin B. Structural resemblance between dioscorin A and crude yam proteins implies that dioscorin A exhibits structural preference even though its content is lower than dioscorin B.

Structural Characterization of Functional Compositions Isolated from Dioscorea Purpurea (Cultivar of Ming-Chien) by Raman Spectroscopy

The structure of functional compositions isolated from D. purpurea (Cultivar of Ming-Chien) was characterized by FT-Raman. After serial isolation and purification, functional compositions of D. purpurea including allantoin, anthocyanin, β-carotene, lecithin, and dioscorin were identified. The shiny crystalline of allantoin was stable enough to tolerate with dramatic change in pH as evidenced by the consistency of FT-Raman spectra. Spectroscopic results indicated that anthocyanin was responsible for the distinguished purple coloration in D. purpurea. A very small quantity of egg-yolklike compound extracted by hexane was identified as a mixture of β-carotene and lecithin Raman stretching of amide I at 1668 cm-1 and amide III at 1241 cm-1 indicated that the structure of dioscorin, the major storage protein in yams, was mostly in anti-parallel β−sheet. And a slightly conformational difference in the protein structure was detected when the protein was treated with acetone and alcohol, respectively

Solid-state NMR analysis of steroidal conformation of 17α- and 17β-estradiol in the absence and presence of lipid environment

Solid-state {(1)H}(13)C cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopy has been applied to 17β-estradiol (E2) and 17α-estradiol (E2α), to analyze the steroidal ring conformations of the two isomers in the absence and presence of lipids at the atomic level. In the absence of lipid, the high-resolution (13)C NMR signals of E2 in a powdered form show only singlet patterns, suggesting a single ring conformation. In contrast, the (13)C signals of E2α reveal multiplet patterns with splittings of 20-300Hz, implying multiple ring conformations. In the presence of a mimic of the lipid environment, made by mixing 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC) in a molar ratio 3:1, E2 and E2α revealed multiplet patterns different from those seen in the absence of lipids, indicating that the two isomers adopt multiple conformations in the lipid environment. In this work, on the basis of chemical shift isotropy and anisotropy analysis, we demonstrated that E2 and E2α prefer to adopt multiple steroidal ring conformations in the presence of a lipid environment, distinct from that observed in solution phase and powdered form.