Ultrasensitive DNA methyltransferase activity sensing and inhibitor evaluation with highly photostable upconversion nanoparticle transducer

Fluorescence turn-off strategy for sensitive detection of DNA methyltransferase activity based on DNA-templated gold nanoclusters

DNA methylation results in a variety of human diseases and the DNA methylation process is mediated by DNA methyltransferases, which have therefore become potential targets for disease treatment. In this study, a turn-off nanogold biological probe system was successfully created for determining the activity of DNA methyltransferases (M.SssI MTase). A dumbbell-shaped DNA probe with a site-recognizable region of M. SssI MTase and a fluorescent signal probe based on a DNA-templated gold nanocluster (DNA-AuNC) probe combined for the quantitative detection of M. SssI MTase. This dumbbell-shaped DNA probe was methylated by M. SssI MTase, and the dumbbell-shaped DNA probe with a methyl group was recognized by an endonuclease (GlaI) and cleaved into hairpin DNA. The dGTP was added to the 3'-OH terminus of hairpin DNA fragments in the presence of terminal deoxynucleotidyl transferase (TdT), and the hairpin DNA was extended with a G-rich sequence that can be used as an inactivation probe. When the inactivation probe was combined with the signal probe, the fluorescent signal disappeared due to the photoinduced electron transfer effect. Methyltransferase activity was then detected based on the turn-off principle of the fluorescence signal from the DNA-AuNCs. The bioprobe enabled sensitive detection of M. SssI MTase with a detection limit of 0.178 U mL^-1 and good specificity. The bioprobe demonstrated good detection efficiency in both human serum and cell lysates, and its unique fluorescence turn-off mechanism provided good resistance to interference, thus increasing its potential application in complex biological samples. Moreover, it is suitable for screening and assessing the inhibitory activity of M. SssI MTase inhibitors, and therefore has significant potential for disease diagnosis and drug discovery.

Ratiometric Electrochemical Biosensing of Methyltransferase Activity

In this work, a novel ratiometric electrochemical readout platform was proposed and developed for the fast and flexible analysis of M.SssI methyltransferase (MTase) activity. In this platform, two hairpin DNAs (H1 and H2) were designed. H1 contains the palindromic sequence of 5′-CCGG-3′ in its stem which could be methylated and hybridize with H2 labeled by methylene blue (MB) as one of the signal reporters on a gold electrode (GE) in the presence of M.SssI MTase. Additionally, a specific immunoreaction was introduced by conjugating an anti-5-methylcytosine antibody, a DNA CpG methylation recognition unit, with 1,3-ferrocenedicarboxylic acid (Fc) as the second signal reporter. The results showed that when the Fc tag approaches, the MB tag was far from the gold electrode surface, resulting in a decrease in the oxidation peak current of MB (IMB) and an increase in the oxidation peak current of Fc (IFc). The ratiometric electrochemical method above shows the linear range of detection was 0 U/mL 40 U/mL with a detection limit of 0.083 U/mL (the mean signal of blank measures þ3s).

Protein-Mediated Fluorescence Resonance Energy Transfer (P-FRET) Probe: Fabrication and Hydroxyl Radical Detection

Fluorescent probes based on fluorescence resonance energy transfer (FRET) are highly promising for diverse bioapplications. The key to constructing FRET probes is to confine the donor and acceptor within a sufficiently close distance. However, the commonly used covalent linkage often requires elaborate design and complex organic synthesis, and sometimes causes changes in the fluorescence properties of the donor and acceptor. Inspired by the binding between small molecules and protein in nature, herein, we propose a protein-mediated strategy to fabricate FRET probe. In such protein-mediated FRET (P-FRET) probe, protein acts as a carrier to simultaneously confine donor and acceptor in its cavity. As a proof of concept, we use bovine serum albumin (BSA) as a model protein, coumarin derivative as a donor and hydroxyl radical (·OH)-responsive dye fluorescein as an acceptor. Through a series of investigations, including binding parameters, fluorescence properties and detection performance, we prove that the construction of P-FRET probe is simple and feasible and the detection is sensitive. Our P-FRET strategy will provide new insights for the design of FRET probes.