Figure 1. The evolution of a methionine-selective protein functionalization strategy.

(a) Existing protein functionalization tactics, and the potential for methionine-selective bioconjugation; R = peptide or protein, R¹ = various organic groups, R² = aryl or ester group (b) Functionalized hypervalent iodine reagents enable methionine-selective protein modification, leading to methionine-based bioorthogonal protein diversification. X = leaving group; R³ = functional payload.