Inert Complexes Unlock Ligand-Accelerated Transition-Metal Catalysis on Proteins.

Area of Science:

• Protein chemistry
• Catalysis
• Bioconjugation

Background:

• Traditional metal catalysis on proteins requires high metal loadings, leading to non-catalytic conditions and potential protein damage.
• Developing truly catalytic metal-based reactions on proteins is crucial for advancing protein engineering and post-translational modification.

Purpose of the Study:

• To develop inert metal-ligand complexes for efficient, substoichiometric ligand-accelerated catalysis (LAC) on proteins.
• To demonstrate the utility of these complexes in key protein modification reactions.

Main Methods:

• Screening of metal-ligand complexes for stability and inertness in protein environments.
• Utilizing bathocuproine disulfonic acid disodium salt (BCS) with nickel (Ni-BCS) and copper (Cu-BCS) for protein catalysis.
• Investigating reaction mechanisms using in situ intermediates and assessing catalyst efficiency and protein integrity.

Main Results:

• Ni-BCS enabled efficient depropargylation of GFP-ProcLys at 5 mol% catalyst with a turnover number (TON) of ≈20, surpassing previous methods.
• Cu-BCS facilitated copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) on proteins at 10 mol% with minimal residual copper and no protein oxidation.
• Mechanistic studies revealed an in situ Ni-H intermediate mediating various protein transformations.

Conclusions:

• Biologically inert metal-ligand complexes, particularly Ni-BCS and Cu-BCS, enable robust and efficient LAC on proteins under substoichiometric conditions.
• This approach overcomes limitations of traditional metal catalysis on proteins, expanding the scope of post-translational mutagenesis.
• A rational ligand-design framework for protein-level transition-metal catalysis has been established, advancing protein chemistry.