Small Molecule Control of Protein Function through Staudinger Reduction

Using small molecules to control the function of proteins in live cells with complete specificity is highly desirable, but challenging. Here we report a small molecule switch that can be used to control protein activity. The approach uses a phosphine-mediated Staudinger reduction to activate protein function. Genetic encoding of an ortho-azidobenzyloxycarbonyl amino acid using a pyrrolysyl tRNA synthetase/tRNA(CUA) pair in mammalian cells enables the site-specific introduction of a small molecule-removable protecting group into the protein of interest. Strategic placement of this group renders the protein inactive until deprotection through a bioorthogonal Staudinger reduction delivers the active, wild-type protein. This developed methodology was applied to the conditional control of several cellular processes, including bioluminescence (luciferase), fluorescence (EGFP), protein translocation (nuclear localization sequence), DNA recombination (Cre), and gene editing (Cas9).