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Affinity Bioorthogonal Chemistry (ABC) Tags for Site-selective Conjugation, On-resin Protein-Protein Coupling, and Purification of Protein Conjugates.

The site-selective functionalization of proteins has broad application in chemical biology, but can be limited when mixtures result from incomplete conversion or the formation of protein containing side products. It is shown here that when proteins are covalently tagged with pyridyl-tetrazines, the Ni-IDA resins commonly used for His-tags can be directly used for protein affinity purification. These Affinity Bioorthogonal Chemistry tags (ABC-tags) serve a dual role by enabling affinity-based protein purification through metal chelation and still maintain their rapid kinetics in bioorthogonal reactions. ABC-tagging can be applied in conjunction with a range of site-selective bioconjugation methods, and is demonstrated for a range of proteins tagged at the C-terminus, N-terminus or at internal positions. ABC-tagged proteins can also be purified from complex mixtures including cell lysate. Importantly, the combination of siteselective conjugation and clean-up with ABC-tagged proteins also allows for facile on-resin reactions for cleanly preparing proteinprotein conjugates in minutes.