Site-selective protein modification via peptide-directed proximity catalysis

Proximity catalysis exploits ligand-binding for localised, catalytic protein modification. In this work, we introduce catalyst-functionalised peptides as versatile ligands for this approach. Through the functionalisation of target-binding peptides with pyridinium oximes catalysts, we show that model proteins can be site-selectively modified with a variety of N-acyl-N-alkylsulfonamide reagents, to introduce common functionalities including fluorophores and affinity handles to the protein surface. Critically, we show that simple changes to the peptide-catalyst structure, moving the pyridinium oxime from N- to C-terminus, alter the site of modification. This opens up possibilities to develop peptide libraries for a particular target protein, and subsequently tuning the modification site for a given application.