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Biomedical subjects

Zhihong Cheng

Publications and source records attributed to Zhihong Cheng.

11 recordsLinked to original sources
PubMed2006

Structural and functional insights into the human Upf1 helicase core.

Nonsense-mediated mRNA decay (NMD) is an mRNA surveillance pathway that recognizes and degrades aberrant mRNAs containing premature stop codons. A critical protein in NMD is Upf1p, which belongs to the helicase super family 1 (SF1), and is thought to utilize the energy of ATP hydrolysis to promote transitions in the structure of RNA or RNA-protein complexes. The crystal structure of the catalytic core of human Upf1p determined in three states (phosphate-, AMPPNP- and ADP-bound forms) reveals an overall structure containing two RecA-like domains with two additional domains protruding from the N-terminal RecA-like domain. Structural comparison combined with mutational analysis identifies a likely single-stranded RNA (ssRNA)-binding channel, and a cycle of conformational change coupled to ATP binding and hydrolysis. These conformational changes alter the likely ssRNA-binding channel in a manner that can explain how ATP binding destabilizes ssRNA binding to Upf1p.

Adenosine Diphosphate↗
PubMed2006

Effects of solid-state enzymatic treatments on the antioxidant properties of wheat bran.

This study evaluated the potential of solid-state enzyme treatments to release insoluble bound antioxidants such as phenolic acids from wheat bran, thereby improving its extractable and potentially bioaccessible antioxidant properties including scavenging capacities against peroxyl (ORAC), ABTS cation, DPPH and hydroxyl radicals, total phenolic contents, and phenolic acid compositions. Investigated enzyme preparations included Viscozyme L, Pectinex 3XL, Ultraflo L, Flavourzyme 500L, Celluclast 1.5L, and porcine liver esterase. Results showed significant dose-dependent increases in extractable antioxidant properties for some enzyme preparations, and Ultraflo L was found to be the most efficient enzyme, able to convert as much as 50% of the insoluble bound ferulic acid in wheat bran to the soluble free form. The effect of moisture content on these solid-state enzyme reactions was also evaluated and found to be dependent on enzyme concentration. These data suggest that solid-state enzyme treatments of wheat bran may be a commercially viable post-harvest procedure for improving the bioaccessibility of wheat antioxidants.

Antioxidants↗
PubMed2006

High-throughput relative DPPH radical scavenging capacity assay.

A high-throughput relative 2,2-diphenyl-1-picryhydrazyl (DPPH) radical scavenging capacity (RDSC) assay was developed and validated in the present study. This RDSC assay is easy to perform and has acceptable accuracy (90-110% recovery), precision [3.9-7.0% pooled relative standard deviation (RSD)], and reproducibility (2.2 and 3.5% interday and intraday RSD). This assay reports the RDSC values for antioxidant samples, which make it possible to compare the DPPH radical scavenging capacities of antioxidants determined in different laboratories. The RDSC assay may be conducted in aqueous alcohol and acetone for hydrophilic antioxidants or in the organic solvents for lipophilic antioxidants without solubilizing agents, which makes it possible to directly compare the radical scavenging capacities of hydrophilic and lipophilic antioxidants. In addition, the high-throughput RDSC assay could be utilized for EC50 value estimation. The high-throughput RDSC assay may be used for screening and investigating potential natural antioxidants.

Antioxidants↗
PubMed2006

Effects of postharvest treatment and heat stress on availability of wheat antioxidants.

This research evaluated the effects of postharvest treatment and heat stress on the availability of wheat antioxidants using Ankor and Trego wheat varieties. The grain, bran, and 40-mesh bran samples of both Ankor and Trego wheat were kept at 25, 60, and 100 degrees C for 9 days. Samples taken at day 0, 1, 2, 3, 5, and 9 were extracted with pure ethanol and examined for antioxidant properties including the scavenging activity against peroxyl (ORAC), cation ABTS, and 2,2-diphenyl-1-picryhydrazyl (DPPH.) radicals, as well as total phenolic content (TPC) and phenolic acid composition. Both heat stress and postharvest treatment significantly altered the antioxidant properties of wheat grain fractions. The ORAC values of Ankor bran and corresponding 40-mesh bran samples kept at 100 degrees C for 9 days reduced to 61 and 40% of that at day 0 on a per dry weight basis, respectively, while the ORAC values of the grain samples showed no significant change. The overall loss of DPPH. scavenging capacity was 38 and 100% for the bran and 40-mesh Ankor bran samples, respectively, and was 47 and 60% in the bran and 40-mesh Trego bran samples, respectively, whereas no reduction was detected in the grain samples under the same heat stress. Heat stress and postharvest treatment had similar effects on ABTS.+ scavenging capacities and TPC values of grain and fractions of both varieties. These data suggest that whole grain as opposed to its fractions is a preferred form of long-term storage for better preserving natural antioxidants and that the reduction of the particle size may accelerate the loss of natural antioxidants in wheat bran during storage and thermal processing but may enhance the releasable amount of wheat antioxidants from bran.

Agriculture↗
PubMed2006

Chemical compositions, antioxidant capacities, and antiproliferative activities of selected fruit seed flours.

Seed flours from black raspberry, red raspberry, blueberry, cranberry, pinot noir grape, and chardonnay grape were examined for their total fat content, fatty acid composition, total phenolic content (TPC), total anthocyanin content (TAC), radical scavenging capacities against the peroxyl (ORAC) and stable DPPH radicals, chelating capacity against Fe(2+), and antiproliferative activities using the HT-29 colon cancer cell line. Significant levels of fat were detected in the fruit seed flours and their fatty acid profiles may differ from those of the respective seed oils. Cranberry seed flour had the highest level of alpha-linolenic acid (30.9 g/100 g fat) and the lowest ratio of n-6/n-3 fatty acids (1.2/1). The ORAC value of the chardonnay seed flour was 1076.4 Trolox equivalents mumol/g flour, and its TPC was 186.3 mg gallic acid equivalents/g flour. These values were 3-12 times higher than the other tested fruit seed flours. Furthermore, the ORAC value was significantly correlated to the TPC under the experimental conditions (P < 0.05). These fruit seed flours also differed in their TAC values and Fe(2+)-chelating capacities. In addition, black raspberry, cranberry, and chardonnay grape seed flour extracts were evaluated for their antiproliferative effects using HT-29 colon cancer cells. All three tested seed flour extracts significant inhibited HT-29 cell proliferation. The data from this study suggest the potential of developing the value-added use of these fruit seed flours as dietary sources of natural antioxidants and antiproliferative agents for optimal human health.

Anthocyanins↗
PubMed2005

Crystal structure and functional analysis of DEAD-box protein Dhh1p.

The control of mRNA translation and degradation are critical for proper gene expression. A key regulator of both translation and degradation is Dhh1p, which is a DEAD-box protein, and functions both to repress translation and enhance decapping. We describe the crystal structure of the N- and C-terminal truncated Dhh1p (tDhh1p) determined at 2.1 A resolution. This reveals that, like other DEAD-box proteins, tDhh1p contains two RecA-like domains, although with a unique arrangement. In contrast to eIF4A and mjDEAD, in which no motif interactions exist, in Dhh1p, motif V interacts with motif I and the Q-motif, thereby linking the two domains together. Electrostatic potential mapping combined with mutagenesis reveals that motifs I, V, and VI are involved in RNA binding. In addition, trypsin digestion of tDhh1p suggests that ATP binding enhances an RNA-induced conformational change. Interestingly, some mutations located in the conserved motifs and at the interface between the two Dhh1 domains confer dominant negative phenotypes in vivo and disrupt the conformational switch in vitro. This suggests that this conformational change is required in Dhh1 function and identifies key residues involved in that transition.

Amino Acid Sequence↗
PubMed2005

Identification of volatile basic components in tobacco by headspace liquid-phase microextraction coupled to matrix-assisted laser desorption/ionization with Fourier transform mass spectrometry.

A method incorporating headspace liquid-phase microextraction (HS-LPME) coupled to matrix-assisted laser desorption/ionization (MALDI) with Fourier transform mass spectrometry (FTMS) was established to analyze volatile basic components in tobacco. The sample preparation volume for MALDI-MS was compatible with the volume of the solvent microdrop in the HS-LPME procedure. The pH and the polarity of the solvent for HS-LPME were adjusted by choice of the MALDI matrix and matrix additive. Based on the elemental composition and tandem mass spectrometry information, 25 volatile nitrogenous compounds in tobacco were detected and identified. The approach is fast and sensitive, and has the potential for automation for high-throughput analysis. This approach offers an alternative method for analysis of trace volatile organic compounds in complex samples.

Gas Chromatography-Mass Spectrometry↗
PubMed2005

Anti-inflammatory activities of aqueous extract from Radix Ophiopogon japonicus and its two constituents.

To provide some pharmacological evidence for its clinical use in inflammatory diseases, anti-inflammatory effect of the aqueous extract from Radix Ophiopogon japonicus (ROJ-ext), a traditional Chinese herb, was examined in mouse and rat models. ROJ-ext significantly inhibited xylene-induced ear swelling and carrageenan-induced paw edema in mice when given orally at doses of 25 and 50 mg/kg. Moreover, ROJ-ext also remarkably suppressed carrageenan-induced pleural leukocyte migration in rats and zymosan A-evoked peritoneal total leukocyte and neutrophil migration in mice, while had no obvious effect on pleural prostaglandin E2 level. Furthermore, two active compounds were isolated from ROJ-ext and identified as ruscogenin and ophiopogonin D. As the results, ROJ-ext, ruscogenin and ophiopogonin D dose-dependently reduced phorbol-12-myristate-13-acetate (PMA)-induced adhesion of HL-60 cells to ECV304 cells, with IC50 of 42.85 microg/ml, 7.76 nmol/l and 1.38 nmol/l, respectively. However, they showed no inhibitory effect on PMA-induced cyclooxygense-2 (COX-2) mRNA expression in ECV304 cells. Ruscogenin and ophiopogonin D also notably decreased zymosan A-induced peritoneal leukocyte migration, in comparison with ROJ-ext. These results demonstrate that ROJ-ext presents remarkable anti-inflammatory activity and ruscogenin and ophiopogonin D are two of its active components, which supported its traditional use in the treatment of various diseases associated with inflammation.

Aconitum↗
PubMed2004

Crystal structure of Ski8p, a WD-repeat protein with dual roles in mRNA metabolism and meiotic recombination.

Ski8p is a WD-repeat protein with an essential role for the Ski complex assembly in an exosome-dependent 3'-to-5' mRNA decay. In addition, Ski8p is involved in meiotic recombination by interacting with Spo11p protein. We have determined the crystal structure of Ski8p from Saccharomyces cerevisiae at 2.2 A resolution. The structure reveals that Ski8p folds into a seven-bladed beta propeller. Mapping sequence conservation and hydrophobicities of amino acids on the molecular surface of Ski8p reveals a prominent site on the top surface of the beta propeller, which is most likely involved in mediating interactions of Ski8p with Ski3p and Spo11p. Mutagenesis combined with yeast two-hybrid and GST pull-down assays identified the top surface of the beta propeller as being required for Ski8p binding to Ski3p and Spo11p. The functional implications for Ski8p function in both mRNA decay and meiotic recombination are discussed.

Amino Acid Sequence↗
PubMed2002

[Regulated expression of insulin gene in non-beta cell].

OBJECTIVE: To engineer 293 cells to an artificial beta cell line which secrets insulin in response to stimulation by doxycycline. METHODS: A recombined expression vector, pTRE2mINS, which contained both of the tetracycline response element and proinsulin gene, was constructed. This vector was co-transfected with plasmid pTK-Hyg encoding hygromycin in the tet293 cells, which express the reverse tetracycline-controlled transactivator stably. Following hygromycin screening, the survived cells expressing insulin were selected and enriched. Then, doxycycline one of tetracycline derivatives, was used to control the expression of insulin in these cells. At the levels of mRNA and protein, the regulating effect of doxycycline in culture medium on the expression of proinsulin gene was estimated respectively with Northern blotting, RT-PCR, and radioimmunoassay. RESULTS: Of the 28 hygromycin resistant cell strains, we selected one cell strain secreting insulin not only automatically, but in response to stimulation by doxycycline was selected. The cells secreted insulin at the rate of 9.7 U/24 h/1.0 x10(6) cells without doxycy cline treatment, and the amount of secreted insulin increased to 241.0 U/24 h/1.0 x 10(6) cells (25-fold) in the presence of doxycycline(1 000 ng/ml). I insulin secretion was induced by doxycycline in a dose dependent manner. CONCLUSION: Human proinsulin gene was transfected successfully and expressed efficiently in 293 cells, and the expression was modulated by tetracycline and its derivatives, improving the accuracy, safety, and reliability for the gene therapy of diabetes mellitus.

Cell Line↗