OPA-based bifunctional linker for protein labeling and profiling.

Lysine residues have been considered as a routine conjugating site for protein chemical labeling and modification. The commercially available lysine-labeling agents have several limitations in labeling efficiency, stability, and cost. To pursue alternative protein lysine-labeling strategies, herein, we report the development of an ortho-phthalaldehyde (OPA)-based bifunctional linker suitable for protein chemical labeling and profiling. Among three designed OPA-based bifunctional linkers, OPA-NH-alkyne 5 was proved to be optimal for protein labeling with minimal protein turbidity. We further demonstrated OPA-NH-alkyne 5 was applicable for immediate capture of protein or proteome chemical labeling.