Kong-Hung Sze

Effects of dissolved oxygen, pH, and anions on the 2,3-dichlorophenol degradation by photocatalytic reaction with anodic TiO2 nanotube films

In this study, the highly-ordered TiO(2) nanotube (TNT) arrays on titanium sheets were prepared by an anodic oxidation method. Under UV illumination, the TNT films demonstrated the higher photocatalytic activity in terms of 2,3-dichlorophenol (2,3-DCP) degradation in aqueous solution than the conventional TiO(2) thin films prepared by a sol-gel method. The effects of dissolved oxygen (DO) and pH on the photocatalytic degradation of 2,3-DCP were investigated. The results showed that the role of DO in the 2,3-DCP degradation with the TNT film was significant. It was found that 2,3-DCP in alkaline solution was degraded and dechlorinated faster than that in acidic solution whereas dissolved organic carbon removal presented an opposite order in dependence of pH. In the meantime, some main intermediate products from 2,3-DCP degradation were identified by a (1)H NMR technique to explore a possible degradation pathway. A major intermediate, 2-chlororesorcinol, was identified from the 2,3-DCP decomposition as a new species compared to the findings in previous reports. Photocatalytic deactivation was also evaluated in the presence of individual anions (NO(3)(-), Cl(-), SO(4)(2-), and H(2)PO(4)(-)). The inhibition degree of photocatalytic degradation of 2,3-DCP caused by these anions can be ranked from high to low as SO(4)(2-)>Cl(-)>H(2)PO(4)(-)>NO(3)(-). The observed inhibition effect can be attributed to the competitive adsorption and the formation of less reactive radicals during the photocatalytic reaction.

Gradient and sensitivity enhancement of 2D TROSY with water flip-back, 3D NOESY-TROSY and TOCSY-TROSY experiments

AbstractPreviously we demonstrated a sensitivity enhancement of the original TROSY experiment by a factor of

Interaction between trichosanthin, a ribosome-inactivating protein, and the ribosomal stalk protein P2 by chemical shift perturbation and mutagenesis analyses

\sqrt 2

Mapping the binding site for the GTP-binding protein Rac-1 on its inhibitor RhoGDI-1

by the use of the sensitivity enhanced TROSY (en-TROSY) scheme. Here, we develop a gradient and sensitivity enhanced TROSY experiment (gs-TROSY), which is designed to select magnetization transfer pathways that suppress spectral artifacts and reduce the number of required phase cycles while having minimal loss of sensitivity. Both of these experimental methods (en-TROSY and gs- TROSY) have been combined with a water flip-back scheme which provides a further increase in sensitivity for labile NH groups by avoiding water saturation. We also apply these TROSY schemes to 3D NOESY-TROSY and 3D TOCSY-TROSY experiments.

A Rigidifying Salt-Bridge Favors the Activity of Thermophilic Enzyme at High Temperatures at the Expense of Low-Temperature Activity.

Publisher Summary This chapter describes exchange processes and determination of ligand conformation and protein-ligand contacts. Nuclear magnetic resonance (NMR) spectroscopy can provide information on many different aspects of protein-ligand interactions, ranging from the determination of the complete structure of a protein-ligand complex to focusing on selected features of the interactions between the ligand and protein by using reporter groups on the ligand or the protein. In addition to the structural information, dynamic, kinetic, and thermodynamic aspects of ligand binding are presented. Early analysis of ligand binding focused on measurements of relaxation times, chemical shifts, and coupling constants, which gave relatively limited, though valuable, structural information. The first step in any study of protein-ligand interactions by NMR is to establish to which region of exchange the spectrum corresponds (or, more correctly, the resonances of interest, because different resonances can show different exchange behavior).

Goldfish spexin: solution structure and novel function as a satiety factor in feeding control

Trichosanthin (TCS) is a type I ribosome-inactivating protein that inactivates ribosome by enzymatically depurinating the A4324 at the α-sarcin/ricin loop of 28S rRNA. We have shown in this and previous studies that TCS interacts with human acidic ribosomal proteins P0, P1 and P2, which constitute the lateral stalk of eukaryotic ribosome. Deletion mutagenesis showed that TCS interacts with the C-terminal tail of P2, the sequences of which are conserved in P0, P1 and P2. The P2-binding site on TCS was mapped to the C-terminal domain by chemical shift perturbation experiments. Scanning charge-to-alanine mutagenesis has shown that K173, R174 and K177 in the C-terminal domain of TCS are involved in interacting with the P2, presumably through forming charge–charge interactions to the conserved DDD motif at the C-terminal tail of P2. A triple-alanine variant K173A/R174A/K177A of TCS, which fails to bind P2 and ribosomal stalk in vitro, was found to be 18-fold less active in inhibiting translation in rabbit reticulocyte lysate, suggesting that interaction with P-proteins is required for full activity of TCS. In an analogy to the role of stalk proteins in binding elongation factors, we propose that interaction with acidic ribosomal stalk proteins help TCS to locate its RNA substrate.

Trapping of Phenylacetaldehyde as a Key Mechanism Responsible for Naringenin’s Inhibitory Activity in Mutagenic 2-Amino-1-methyl-6-phenylimidazo [4,5-b]Pyridine Formation

Acrolein (ACR) and 4-hydroxy-trans-2-nonenal (HNE) are two cytotoxic lipid-derived alpha,beta-unsaturated aldehydes which have been implicated as causative agents in the development of carbonyl stress-associated pathologies. In this study, 21 natural polyphenols were screened to identify effective scavenging agents of ACR and/or HNE in simulated physiological conditions. It was found that flavan-3-ols, theaflavins, cyanomaclurin, and dihydrochalcones effectively trapped ACR and HNE by working as sacrificial nucleophiles. The most effective one was phloretin, which quenched up to 99.6% ACR in 90 min and 90.1% HNE in 24 h. Subsequent LC-MS/MS analysis showed that these effective polyphenols formed adducts with ACR and HNE. A major adduct formed from phloretin and ACR was purified, and its structure was characterized by LC-MS and NMR spectroscopy as diACR-conjugated phloretin. The chemical nature of interactions between ACR and polyphenols was proposed as the Michael addition reaction of phloretin to the C horizontal lineC double bond of ACR, followed by the formation of hemiacetal between the hydroxyl group in the A ring of phloretin and the C horizontal lineO carbonyl group in ACR, thus yielding more stable products. Findings of the present study highlighted certain classes of polyphenols as promising sequestering agents of alpha,beta-unsaturated aldehydes to inhibit or restrain carbonyl stress-associated diseases.

The biosynthetic pathway for a thousand-year-old natural food colorant and citrinin in Penicillium marneffei

BACKGROUND Members of the Rho family of small GTP-binding proteins, such as Rho, Rac and Cdc42, have a role in a wide range of cell responses. These proteins function as molecular switches by virtue of a conformational change between the GTP-bound (active) and GDP-bound (inactive) forms. In addition, most members of the Rho and Rac subfamilies cycle between the cytosol and membrane. The cytosolic guanine nucleotide dissociation inhibitors, RhoGDIs, regulate both the GDP/GTP exchange cycle and the membrane association/dissociation cycle. RESULTS We have used NMR spectroscopy and site-directed mutagenesis to identify the regions of human RhoGDI-1 that are involved in binding Rac-1. The results emphasise the importance of the flexible regions of both proteins in the interaction. At least one specific region (residues 46-57) of the flexible N-terminal domain of RhoGDI, which has a tendency to form an amphipathic helix in the free protein, makes a major contribution to the binding energy of the complex. In addition, the primary site of Rac-1 binding on the folded domain of RhoGDI involves the beta4-beta5 and beta6-beta7 loops, with a slight movement of the 3(10) helix accompanying the interaction. This binding site is on the same face of the protein as the binding site for the isoprenyl group of post-translationally modified Rac-1, but is distinct from this site. CONCLUSIONS Isoprenylated Rac-1 appears to interact with three distinct sites on RhoGDI. The isoprenyl group attached to the C terminus of Rac-1 binds in a pocket in the folded domain of RhoGDI. This is distinct from the major site on this domain occupied by Rac-1 itself, which involves two loops at the opposite end to the isoprenyl-binding site. It is probable that the flexible C-terminal region of Rac-1 extends from the site at which Rac-1 contacts the folded domain of RhoGDI to allow the isoprenyl group to bind in the pocket at the other end of the RhoGDI molecule. Finally, the flexible N terminus of RhoGDI-1, and particularly residues 48-58, makes a specific interaction with Rac-1 which contributes substantially to the binding affinity.