Exploring the Potential of Ultrafast Arylation for Capping Cysteine Residues with Fixed Charge Modifications.

Area of Science:

• Proteomics and Mass Spectrometry
• Chemical Biology
• Protein Chemistry

Background:

• Cysteine (Cys) modification is crucial in proteomics for peptide generation and mass spectrometry (MS) identification.
• Electrophilic Cys arylation is less common than other blocking strategies.
• A novel reagent, CAP4, enables rapid and selective electrophilic Cys arylation.

Purpose of the Study:

• To investigate the fragmentation behavior of Cys residues modified with CAP4 under different MS conditions (HCD and ETD).
• To evaluate the utility of CAP4 in a bottom-up proteomics workflow.
• To compare CAP4 modification efficiency and outcomes against a standard method (iodoacetamide).

Main Methods:

• Electrophilic arylation of Cysteine residues using N-methyl-2-methylsulfonylpyridinium (CAP4).
• Analysis of CAP4-modified peptides using higher-energy collisional dissociation (HCD) and electron-transfer dissociation (ETD) in mass spectrometry.
• Bottom-up proteomics workflow using a model protein mixture with CAP4 and iodoacetamide modifications.

Main Results:

• CAP4 modification introduces a fixed charge, influencing fragmentation pathways in both HCD and ETD.
• Observed abundant side chain losses in HCD and formation of a charge-state dependent beta radical in ETD.
• Achieved comparable sequence coverage and modified peptide identification using CAP4 (5 min) versus iodoacetamide (1 h).

Conclusions:

• CAP4 modification significantly impacts peptide fragmentation, offering unique insights into dissociation mechanisms.
• Despite fragmentation influence, CAP4 is effective for rapid Cys modification in bottom-up proteomics.
• CAP4 presents a viable, fast alternative to iodoacetamide for enhancing Cys-containing peptide identification in MS-based proteomics.