A Metabolic Alkene Reporter for Spatiotemporally Controlled Imaging of Newly Synthesized Proteins in Mammalian Cells

The nonsymmetrical spatial distribution of newly synthesized proteins in animal cells plays a central role in many cellular processes. Here, we report that a simple alkene tag, homoallylglycine (HAG), was co-translationally incorporated into a recombinant protein as well as endogenous, newly synthesized proteins in mammalian cells with high efficiency. In conjunction with a photoinduced tetrazole-alkene cycloaddition reaction ("photoclick chemistry"), this alkene tag further served as a bioorthogonal chemical reporter both for the selective protein functionalization in vitro and for a spatiotemporally controlled imaging of the newly synthesized proteins in live mammalian cells. This two-step metabolic alkene tagging-photocontrolled chemical functionalization approach may offer a potentially useful tool to study the role of spatiotemporally regulated protein synthesis in mammalian cells.