DogMask: A Genetically Encoded Switch for Conditional Protein Conjugation.

Protein conjugation enables the modular assembly of functional proteins but is largely incompatible with stimulus-responsive platforms due to spontaneous reactivity. Here, we present DogMask, a genetically encoded platform that achieves input-triggered protein conjugation by autoinhibiting a spontaneous conjugation platform, DogCatcher, with a competitive inhibitor mask. DogMask exhibits no detectable background conjugation and rapid activation in response to distinct inputs-including clinically relevant proteases and a photocleavable non-standard amino acid variant achieving 70% cleavage efficiency, exceeding prior benchmarks-properties enabling robust intracellular control of transcription, RNA editing, and enzyme reconstitution, with both substantially reduced background and enhanced response relative to inducible dimerization systems.