Acidic Extracellular pH-Activated Allosteric DNA Nanodevice for Fluorescence Imaging of APE1 Activity in Tumor Cells.

Allostery is a phenomenon where the binding of a ligand at one allosteric site influences the affinity for another ligand at an active site. Different from orthosteric regulation, it allows for more precise control of biomolecular activity and enhances the stability of the molecules. Inspired by allosteric regulation of natural molecules, we present a Y-shaped allosteric DNA nanodevice, termed YssAP, that was pH-responsive and functionalized with the AS1411 aptamer for accurate fluorescence imaging of human apurinic/apyrimidinic endonuclease (APE1) activity in tumor cells. With rational design, YssAP could not be cut by APE1, and Cy5 was in the proximity of BHQ2, leading to suppressed signal emission. In contrast, since acidic pH acted as an allosteric effector, YssAP underwent a conformational change into an activated DNA probe (YdsAP) at acidic extracellular pH. After entering the tumor cell via the specific recognition of AS1411 aptamer, the overexpressed APE1 in the tumor cell cut the AP site on YdsAP. Cy5 moved far away from BHQ2, resulting in a strong signal output. Compared with the direct construction of the APE1 substrate, allosteric DNA nanodevices have more accurate imaging effects, which can be precisely adjusted by changing the switching state. We anticipate that this strategy will be applied in the screening of APE1 inhibitors and precise tumor diagnosis.