Assay of DNA methyltransferase 1 activity based on uracil-specific excision reagent digestion induced G-quadruplex...

DNA methylation catalyzed by DNA methyltransferase plays an important role in many biological processes including gene transcription, genomic imprinting and cellular differentiation. Herein, a novel and effective electrochemical method for the assay of DNA methyltransferase 1(DNMT1) activity has been successfully developed by using uracil-specific excision reagent (USER) induced G-quadruplex formation. Briefly, double stranded DNA containing the recognition sequence of DNMT1 is immobilized on the electrode. Among them, one strand (DNA S1) contains G-rich sequence and a cytosine base, while the supplement strand (DNA S2) cotains C-rich sequence and a methylated cytosine. Through the activity of DNMT1, the hemimethylated CG recognition sequence of the double stranded DNA are methylated and DNA S2 strand is cleaved and removed after the subsequently treatment with EpiTect fast bisulfite conversion kits and USER, leaving the DNA S1 to form the G-quadruplex-hemin DNAzyme for signal amplification. Under optimal-conditions, the method shows wide linear range of 0.1-40 U mL^-1 with a detection limit of 0.06 U mL^-1. Furthermore, the inhibition assay study demonstrates that SGI-1027 can inhibit the DNMT 1 activity with the IC50 values of 6 μM in the presence of 160 μM S-adenosylmethionine. Since this method can detect human DNMT1 activity effectively and has successfully been applied in complex biological samples, it may have great potential in the applications in DNA methylation related clinical practices and biochemical researches.