Autonomous exonuclease III-assisted isothermal cycling signal amplification: a facile and highly sensitive fluorescence DNA glycosylase activity assay.

One common form of DNA damage is the oxidation of guanine to 8-oxo-7,8-dihydroguanine (8-oxoG), which can be carcinogenic. Human 8-oxoguanine DNA glycosylase (hOGG1) is a key base excision repair (BER) enzyme that repairs 8-oxoG, and the expression level of hOGG1 is closely related to many types of human cancers. Herein, a novel and highly sensitive fluorescence biosensing platform for hOGG1 activity detection has been constructed based on autonomous exonuclease III (Exo III)-assisted signal amplification. Two hairpin probes (HP1 and HP2) are ingeniously designed. In the presence of hOGG1, HP1 is cleaved at the 8-oxoG site, and the stem is subsequently digested by Exo III, releasing the trigger DNA fragment (tDNA1). Successively, tDNA1 partially hybridizes with HP2 to initiate the Exo III-assisted cycling cleavage to release another trigger DNA fragment (tDNA2), which in turn triggers the cycling cleavage of DNA fluorescence probe (FP). Therefore, large amount of fluorophore fragments are released, leading to a significantly amplified fluorescence signal toward hOGG1 activity detection. A directly measured detection limit down to 0.001 U/mL is obtained, which is much lower than that of the approaches reported in literature. In addition to high sensitivity and good selectivity, the as-proposed strategy also exhibits the advantages of isothermal experimental condition, simplicity, and convenience. Furthermore, the Exo III-assisted autonomous cycling cleavage approach we proposed here is a universal sensing strategy and has great potential in assays of many other biological analytes.