Mass spectrometry-based strategies for protein disulfide bond identification

The formation of disulfide bonds is critical for stabilizing protein structures and maintaining protein functions. It is important to understand the linkages between multiple cysteine residues within a protein. In this review, the analytical approaches using mass spectrometry (MS) for disulfide linkage assignment are classified and discussed. Enzymatic digestion under appropriate conditions followed by various MS detection strategies remains the primary method for cysteine linkage analysis. In-source decay (ISD) and electron transfer dissociation (ETD) have been used to generate significant peptide signals that indicate the identities of peptides involved in disulfide bonds. In addition, chemical labeling and software algorithms were also developed to facilitate the automation of disulfide bond analysis. For proteins with complex disulfide structure, methods involving partial reduction coupled with differential alkylation were demonstrated to be useful. In the past two decades, MS has become one of the most valuable tools for protein disulfide bond analysis. It provides irreplaceable information including the peptide backbone sequences as well as the cysteine connection pattern when coupling with appropriate sample preparations. The related approaches with their unique features can be applied for different aims such as structural characterization or functional studies of proteins.