Insight into an Oxidative DNA-Cleaving DNAzyme: Multiple Cofactors, the Catalytic Core Map and a Highly Efficient Variant.

An oxidative DNA-cleaving DNAzyme (PL) employs a double-cofactor model "X/Cu2+" for catalysis. Herein, we verified that reduced nicotinamide adenine dinucleotide (NADH), flavin mononucleotide, cysteine, dithiothreitol, catechol, resorcinol, hydroquinone, phloroglucinol, o-phenylenediamine, 3,3',5,5'-tetramethylbenzidine, and hydroxylamine acted as cofactor X. According to their structural similarities or fluorescence property, we further confirmed that reduced nicotinamide adenine dinucleotide phosphate (NADPH), 2-mercaptoethanol, dopamine, chlorogenic acid, resveratrol, and 5-carboxyfluorescein also functioned as cofactor X. Superoxide anions might be the commonality behind these cofactors. We subsequently determined the conservative change of individual nucleotides in the catalytic core under four different cofactor X. The nucleotides A4 and C5 are highly conserved, whereas the conservative levels of other nucleotides are dependent on the types of cofactor X. Moreover, we observed that the minor change in the PL's secondary structure affects electrophoretic mobility. Finally, we characterized a highly efficient variant T3G and converted its double-cofactor NADH/Cu2+ to sole-cofactor NADH.

The Triple Roles of Glutathione for a DNA-Cleaving DNAzyme and Development of a Fluorescent Glutathione/Cu2+-Dependent DNAzyme Sensor for Detection of Cu2+ in Drinking Water.

Pistol-like DNAzyme (PLDz) is an oxidative DNA-cleaving catalytic DNA with ascorbic acid as cofactor. Herein, glutathione was induced into the reaction system to maintain reduced ascorbic acid levels for higher efficient cleavage. However, data indicated that glutathione played triple roles in PLDz-catalyzed reactions. Glutathione alone had no effect on PLDz, and showed inhibitory effect on ascorbic acid-induced PLDz catalysis, but exhibited stimulating effect on Cu2+-promoted self-cleavage of PLDz. Further analysis of the effect of glutathione/Cu2+ on PLDz indicated that H2O2 played a key role in PLDz catalysis. Finally, we developed a fluorescent Cu2+ sensor (PL-Cu 1.0) based on the relationship between glutathione/Cu2+ and catalytic activity of PLDz. The fluorescent intensity showed a linear response toward the logarithm concentration of Cu2+ over the range from 80 nM to 30 µM, with a detection limit of 21.1 nM. PL-Cu 1.0 provided only detection of Cu2+ over other divalent metal ions. Ca2+ and Mg2+ could not interfere with Cu2+ detection even at a 1000-fold concentration. We further applied PL-Cu 1.0 for Cu2+ detection in tap and bottled water. Water stored in copper taps overnight had relatively high Cu2+ concentrations, with a maximum 22.3 µM. Trace Cu2+ (52.2 nM) in deep spring was detected among the tested bottled water. Therefore, PL-Cu 1.0 is feasible to detect Cu2+ in drinking water, with a practical application.

New cofactors and inhibitors for a DNA-cleaving DNAzyme: superoxide anion and hydrogen peroxide mediated an oxidative cleavage process.

Herein, we investigated the effects of new cofactors and inhibitors on an oxidative cleavage of DNA catalysis, known as a pistol-like DNAzyme (PLDz), to discuss its catalytic mechanism. PLDz performed its catalytic activity in the presence of ascorbic acid (AA), in which Cu2+ promoted, whereas Fe2+ significantly inhibited the catalytic function. Since Fe2+/AA-generated hydroxyl radicals are efficient on DNA damage, implying that oxidative cleavage of PLDz had no relation with hydroxyl radical. Subsequently, we used Fe2+/H2O2 and Cu2+/H2O2 to identify the role of hydroxyl radicals in PLDz catalysis. Data showed that PLDz lost its activity with Fe2+/H2O2, but exhibited significant cleavage with Cu2+/H2O2. Because Fe2+/H2O2 and Cu2+/H2O2 are popular reagents to generate hydroxyl radicals and the latter also produces superoxide anions, we excluded the possibility that hydroxyl radical participated in oxidative cleavage and confirmed that superoxide anion was involved in PLDz catalysis. Moreover, pyrogallol, riboflavin and hypoxanthine/xanthine oxidase with superoxide anion and hydrogen peroxide generation also induced self-cleavage of PLDz, where catalase inhibited but superoxide dismutase promoted the catalysis, suggesting that hydrogen peroxide played an essential role in PLDz catalysis. Therefore, we proposed a catalytic mechanism of PLDz in which superoxide anion and hydrogen peroxide mediated an oxidative cleavage process.