Allele-Specific Chemical Rescue of Histone Demethylases Using Abiotic Cofactors.

Closely related protein families evolved from common ancestral genes present a significant hurdle in developing member- and isoform-specific chemical probes, owing to their similarity in fold and function. In this piece of work, we explore an allele-specific chemical rescue strategy to activate a "dead" variant of a wildtype protein using synthetic cofactors and demonstrate its successful application to the members of the alpha-ketoglutarate (αKG)-dependent histone demethylase 4 (KDM4) family. We show that a mutation at a specific residue in the catalytic site renders the variant inactive toward the natural cosubstrate. In contrast, αKG derivatives bearing appropriate stereoelectronic features endowed the mutant with native-like demethylase activity while remaining refractory to a set of wild type dioxygenases. The orthogonal enzyme-cofactor pairs demonstrated site- and degree-specific lysine demethylation on a full-length chromosomal histone in the cellular milieu. Our work offers a strategy to modulate a specific histone demethylase by identifying and engineering a conserved phenylalanine residue, which acts as a gatekeeper in the KDM4 subfamily, to sensitize the enzyme toward a novel set of αKG derivatives. The orthogonal pairs developed herein will serve as probes to study the role of degree-specific lysine demethylation in mammalian gene expression. Furthermore, this approach to overcome active site degeneracy is expected to have general application among all human αKG-dependent dioxygenases.