Structural and Molecular Basis of the Catalytic Mechanism of Geranyl Pyrophosphate C6-Methyltransferase: Creation of an Unprecedented Farnesyl Pyrophosphate C6-Methyltransferase

Prenyl pyrophosphate methyltransferases enhance the structural diversity of terpenoids. However, the molecular basis of their catalytic mechanisms is poorly understood. In this study, using multiple strategies, we characterized a geranyl pyrophosphate (GPP) C6-methyltransferase, BezA. Biochemical analysis revealed that BezA requires Mg²⁺ and solely methylates GPP. The crystal structures of BezA and its complex with S-adenosyl homocysteine were solved at 2.10 and 2.56 Å, respectively. Further analyses using site-directed mutagenesis, molecular docking, molecular dynamics simulations, and quantum mechanics/molecular mechanics calculations revealed the molecular basis of the methylation reaction. Importantly, the function of E170 as a catalytic base to complete the methylation reaction was established. We also succeeded in switching the substrate specificity by introducing a W210A substitution, resulting in an unprecedented farnesyl pyrophosphate C6-methyltransferase.     

Biomolecule-Assisted Synthesis of Hierarchical Multilayered Boehmite and Alumina Nanosheets for Enhanced Molybdenum Adsorption

The effective utilization of various biomolecules for creating a series of mesoporous boehmite (γ-AlOOH) and gamma-alumina (γ-Al₂O₃) nanosheets with unique hierarchical multilayered structures is demonstrated. The nature and concentration of the biomolecules strongly influence the degree of the crystallinity, the morphology, and the textural properties of the resulting γ-AlOOH and γ-Al₂O₃ nanosheets, allowing for easy tuning. The hierarchical γ-AlOOH and γ-Al₂O₃ multilayered nanosheets synthesized by using biomolecules exhibit enhanced crystallinity, improved particle separation, and well-defined multilayered structures compared to those obtained without biomolecules. More impressively, these γ-AlOOH and γ-Al₂O₃ nanosheets possess high surface areas up to 425 and 371 m² g⁻¹, respectively, due to their mesoporous nature and hierarchical multilayered structure. When employed for molybdenum adsorption toward medical radioisotope production, the hierarchical γ-Al₂O₃ multilayered nanosheets exhibit Mo adsorption capacities of 33.1–40.8 mg g⁻¹. The Mo adsorption performance of these materials is influenced by the synergistic combination of the crystallinity, the surface area, and the pore volume. It is expected that the proposed biomolecule-assisted strategy may be expanded for the creation of other 3D mesoporous oxides in the future.     

Effect of Fiber Orientation on Nonlinear Damping and Internal Microdeformation in Short-Fiber-Reinforced Natural Rubber

Experimental Techniques - Nonlinear damping with respect to vibration amplitude is particularly important in mechanical dynamics. The addition of short fibers to damping materials is considered to...     

Cyclically near‐resolvable 4‐cycle systems of 2Kv

Fu and Mishima [J. Combin. Des. 10 (2002), pp. 116–125] have utilized the extended Skolem sequence to prove that there exists a 1‐rotationally resolvable $4$‐cycle system of $2K_v$ if and only if $v\equiv 0$ (mod $4$). In this paper, the existence of a cyclically near‐resolvable $4$‐cycle system is discussed, and it is shown that there exists a cyclically near‐resolvable $4$‐cycle system of $2K_v$ if and only if $v\equiv 1$ (mod $4$).     

SiO2/TiO2/Sb2O5/graphite carbon ceramic conducting material: preparation, characterization, and its use as an electrochemical sensor

SiO₂/TiO₂/graphite (STG) electrically conducting material, prepared by the sol–gel processing method, was used as substrate base for the chemical immobilization of Sb(V) by formation of the Ti–O–Sb linkage. The surface modified material, STGSb, was characterized by X-ray photoelectron spectroscopy and scanning electronic microscopy coupled to energy dispersive spectroscopy. The results showed the Sb(V) homogeneously dispersed on the STG matrix surface, with no phase segregation or isolated pure oxide domains. An electrode prepared with the STGSb material was used to adsorb the electroactive cationic dye meldola blue. The modified electrode, STGSb/MB, presented good performance toward electrocatalytic oxidation of the coenzyme β-NADH (nicotinamide adenine dinucleotide). The electrode was shown to be very stable and allowed the electrochemical detection of NADH at low electrode potential (−0.14 V), which is an interesting feature of the system since in this potential range it is possible to minimize surface fouling and electrode passivation. The support material (STGSb) has proven to have great potential to be applied in the construction of various new electrochemical sensors based on cationic dyes presenting redox properties.     

Characterization of iron dinitrosyl species formed in the reaction of nitric oxide with a biological Rieske center

Reactions of nitric oxide with cysteine-ligated iron-sulfur cluster proteins typically result in disassembly of the iron-sulfur core and formation of dinitrosyl iron complexes (DNICs). Here we report the first evidence that DNICs also form in the reaction of NO with Rieske-type [2Fe-2S] clusters. Upon treatment of a Rieske protein, component C of toluene/o-xylene monooxygenase from Pseudomonas sp. OX1, with an excess of NO(g) or NO-generators S-nitroso-N-acetyl-D,L-pencillamine and diethylamine NONOate, the absorbance bands of the [2Fe-2S] cluster are extinguished and replaced by a new feature that slowly grows in at 367 nm. Analysis of the reaction products by electron paramagnetic resonance, M?ssbauer, and nuclear resonance vibrational spectroscopy reveals that the primary product of the reaction is a thiolate-bridged diiron tetranitrosyl species, [Fe(2)(μ-SCys)(2)(NO)(4)], having a Roussin's red ester (RRE) formula, and that mononuclear DNICs account for only a minor fraction of nitrosylated iron. Reduction of this RRE reaction product with sodium dithionite produces the one-electron-reduced RRE, having absorptions at 640 and 960 nm. These results demonstrate that NO reacts readily with a Rieske center in a protein and suggest that dinuclear RRE species, not mononuclear DNICs, may be the primary iron dinitrosyl species responsible for the pathological and physiological effects of nitric oxide in such systems in biology.     

Development and validation of an on-line two-dimensional reversed-phase liquid chromatography-tandem mass spectrometry method for the simultaneous determination of prostaglandins E(2) and F(2alpha) and 13,14-dihydro-15-keto prostaglandin F(2alpha) levels in human plasma

We developed and validated an on-line reverse-phase two-dimensional LC/MS/MS (2D-LC/MS/MS) system for simultaneous determination of the levels of prostaglandin (PG) E(2) as well as PGF(2alpha) and its metabolite 13,14-dihydro-15-keto PGF(2alpha) (F(2alpha)-M) in human plasma. Analytes were extracted by a three-step solid-phase extraction. Samples were then analyzed by on-line 2D-LC/MS/MS with electrospray ionization in negative mode. The 2D-LC system is composed of two reverse-phase analytical columns with a trapping column linking the two analytical columns. While an acidic buffer was used for both separation dimensions, differing organic solvents were employed for each dimension: methanol for the first and acetonitrile for the second to increase resolving power. The 2D-LC/MS/MS method was highly selective and sensitive with a significantly lower limit of quantitation (0.5 pg/mL for PGE(2) and 2.5 pg/mL for PGF(2alpha) and F(2alpha)-M, respectively). Linearity of the 2D-LC/MS/MS system was demonstrated for the calibration ranges of 0.5-50 pg/mL for PGE(2) and 2.5-500 pg/mL for PGF(2alpha) and F(2alpha)-M, respectively. Acceptable precision and accuracy were obtained throughout the calibration curve ranges. This highly selective and sensitive method was successfully utilized to determine the endogenous levels of PGE(2), PGF(2alpha), and F(2alpha)-M in plasma samples from six (four male and two female) normal volunteers. The mean concentrations for each analyte were 0.755 pg/mL for PGE(2), 5.70 pg/mL for PGF(2alpha) and 9.48 pg/mL for F(2alpha)-M.     

Charge-transfer host system composed of 9,10-bis(3,5-dihydroxyphenyl)anthracene and methylviologen

By using 9,10-bis(3,5-dihydroxyphenyl)anthracene as an electron donor and 1,1′-dimethyl-4,4′-bipyri-dinium dichloride as an electron acceptor, a spontaneously resolved charge-transfer (CT) complex is formed. This CT complex can include n-alkyl alcohol molecules as guests, and the DRS of this CT complex change with the type of component guest molecules.