5-Hydroxy-CTP for Orf135 Protein Hydrolysis Activity Assay[1]
This protocol is adapted from research data and provided for reference only. Adjustments may be necessary based on specific experimental requirements.
1. Reagent Preparation: Dissolve 5-Hydroxy-CTP in water to prepare a stock solution of appropriate concentration (e.g., 5μM working solution); Prepare 20mM Tris-HCl buffer (pH 8.5); Prepare 10mM MgCl₂ solution; Prepare 80μg/ml bovine serum albumin (BSA) solution; Prepare 8mM dithiothreitol (DTT) solution; Prepare 10% glycerol solution; Prepare an anion-exchange HPLC column (TSK-GEL DEAE-2SW, 4.6mm × 250mm) and the corresponding mobile phase (50mM phosphate buffer, pH=7.0, containing 20% acetonitrile and 1mM EDTA).
2. Orf135 Protein Preparation: Clone the E. coli orf135 gene into the pGEX-6P-1 glutathione S-transferase (GST) fusion protein expression vector, and transform it into E. coli BL21 strain for expression. Purify the GST-Orf135 fusion protein through ammonium sulfate precipitation, glutathione Sepharose 4B affinity column chromatography, and gel filtration column chromatography. Remove the GST tag using protease and eliminate GST via a glutathione Sepharose 4B column to obtain recombinant Orf135 protein.
3. Pyrophosphatase Activity Assay: In a standard reaction mixture (100μl), add 20mM Tris-HCl (pH=8.5), 10mM MgCl₂, 80μg/ml BSA, 8mM DTT, 10% glycerol, and 5μM 5-Hydroxy-CTP substrate. Pre-incubate the mixture at 30°C for 2 minutes, add an appropriate amount of Orf135 protein (e.g., 0.2pmol for 5-Hydroxy-CTP assay), and incubate at 30°C for 5 minutes.
4. Reaction Termination and Product Analysis: Add 120μl of 10mM EDTA to terminate the reaction. Inject all samples into a anion-exchange column, and elute isocratically with 50mM phosphate buffer (pH=7.0), 20% acetonitrile, and 1mM EDTA at a flow rate of 1ml/min. Detect using an HPLC detection system at UV wavelength, and quantify nucleoside triphosphates and their hydrolyzed products (monophosphates) by measuring the UV absorbance peak area.
Precautions:
(1) The optimal pH for 5-Hydroxy-CTP hydrolysis is 8.5, and the optimal Mg²⁺ activation constant is 1.2mM. The experiment should be conducted at 30°C.
(2) For your safety and health, please wear a lab coat and disposable gloves during operation.
References:
[1] Fujikawa K, Kasai H. The oxidized pyrimidine ribonucleotide, 5-hydroxy-CTP, is hydrolyzed efficiently by the Escherichia coli recombinant Orf135 protein. DNA Repair (Amst). 2002 Jul 17;1(7):571-6. |
