Biotin as a Reactive Handle to Selectively Label Proteins and DNA with Small Molecules

Biotin is a common functional handle for bioconjugation to proteins and DNA, but its uses are limited to protein-containing conjugation partners such as streptavidin and derivatives thereof. Recently, oxaziridine reagents were developed that selectively conjugate the thioether of methionines on the surface of proteins, a method termed redox-activated chemical tagging (ReACT). These reagents generate sulfimide linkages that range in stability depending on the solvent accessibility and substitutions on the oxaziridine. Here we show that oxaziridine reagents react rapidly with the thioether in biotin to produce sulfimide products that are stable for more than 10 d at 37 °C. This method, which we call biotin redox-activated chemical tagging (BioReACT), expands the utility of biotin labeling and enables a predictable and stable chemical conjugation to biomolecules without the need to screen for a suitable methionine conjugation site. We demonstrate the versatility of this approach by producing a fluorescently labeled antibody, an antibody-drug conjugate, and a small molecule-conjugated oligonucleotide. We anticipate that BioReACT will be useful to rapidly introduce biorthogonal handles into biomolecules using biotin, a functional group that is widespread and straightforward to install.