Ligand-Directed Caging Enables the Control of Endogenous DNA Alkyltransferase Activity with Light inside Live Cells.

The control of endogenous protein activity with light inside live cells is helpful for the high spatiotemporal probing of their dynamic roles. Herein, we report the first small-molecule-ligand-directed caging approach to control the endogenous human O 6 -alkylguanine-DNA alkyltransferase (AGT) activity with light, and the caged AGT is constructed from the native intracellular AGT. The photo-responsive O 6 -benzylguanine derivative O 6 -NBG3 is developed to site-specifically cage the AGT's catalytic cysteine residue, and the light irradiation on-demand restores AGT's activity in vitro, in bacteria, and in mammalian cells. With O 6 -NBG3, the alkylated AGT is dealkylated for the first time to recover the DNA repair activity in breast cancer MCF-7 cells by the dose-dependent light irradiation. This decaging strategy enables the localized modulation of endogenous AGT activity with high temporal precision without genetic engineering, which holds great potential for therapeutic applications.