DNA methyltransferase activity assay based on visible light-activated photoelectrochemical biosensor

DNA methylation has important roles in gene regulation and relates to some diseases, especially cancers. Because DNA methylation is catalyzed by DNA methyltransferases (MTase), it is important to detect the activity of DNA MTase. In this work, we developed a novel visible light-activated photoelectrochemical (PEC) biosensor for DNA MTase activity assay, whereby bismuth oxyiodide (BiOI) nanoflake was synthesized as photoactive electrode material, M. SssI MTase as methylation reagent and methyl binding domain protein (MBD1 protein) as methylation recognition element. After cytosine methylation event occurred at the site of 5'-CG-3', it could be probed by MBD1 protein and this protein could be combined tightly with methylated cytosine, which would lead to a decreased photocurrent due to the hindrance towards electron donor transferring to electrode surface by huge-volume protein. The decreased photocurrent was proportional to M. SssI MTase concentration from 0.1 to 50 unit/mL with the detection limit of 0.035 unit/mL (S/N=3). This detection limit was lower than that in some previous reports. This PEC biosensor showed high selectivity and good reproducibility for M. SssI MTase assay. Moreover, this method was successfully applied also to screen DNA MTase inhibitors, indicating that this PEC biosensor could be an alternative platform in anti-cancer pharmaceuticals discovery.