Enzymatic Peptide and Protein Bromination: The BromoTrp Tag.

Bio-orthogonal reactions for modification of proteins and unprotected peptides are of high value in chemical biology. The combination of enzymatic halogenation with transition metal catalysed cross-coupling provides a feasible approach for modification of proteins and unprotected peptides. Using a semi-rational protein engineering approach, variants of the tryptophan 6-halogenase Thal were identified that enable efficient bromination of peptides with a C-terminal tryptophan residue. The substrate scope was explored using di-, tri-, and tetrapeptide arrays leading to the identification of an optimized peptide tag we named BromoTrp tag. This tag was introduced into three model proteins. Preparative scale post-translational bromination was possible with only a single cultivation and purification step using the brominating E. coli coexpression systemBrocoli. Pd-catalysed Suzuki-Miyaura cross-coupling of the bromoarene was achieved using Pd nanoparticle catalysts at 37 °C, highlighting the rich potential of this strategy for bioorthogonal functionalization and conjugation.