Radical Stability Directs Electron Capture and Transfer Dissociation of β-Amino Acids in Peptides

We report on the characteristics of the radical-ion-driven dissociation of a diverse array of beta-amino acids incorporated into alpha-peptides, as probed by tandem electron-capture and electron-transfer dissociation (ECD/ETD) mass spectrometry. The reported results demonstrate a stronger ECD/ETD dependence on the nature of the amino acid side chain for beta-amino acids than for their alpha-form counterparts. In particular, only aromatic (e.g., beta-Phe), and to a substantially lower extent, carbonyl-containing (e.g., beta-Glu and beta-Gln) amino acid side chains, lead to N-C-beta bond cleavage in the corresponding beta-amino acids. We conclude that radical stabilization must be provided by the side chain to enable the radical-driven fragmentation from the nearby backbone carbonyl carbon to proceed. In contrast with the cleavage of backbones derived from alpha-amino acids. ECD of peptides composed mainly of beta-amino acids reveals a shift in cleavage priority from the N-C-beta to the C-alpha-C bond. The incorporation of CH2 groups into the peptide backbone may thus drastically influence the backbone charge solvation preference. The characteristics of radical-driven beta-amino acid dissociation described herein are of particular importance to methods development, applications in peptide sequencing, and peptide and protein modification (e.g., deamidation and isomerization) analysis in life science research. mainly of beta-amino acids reveals a shift in cleavage priority from the N-C-beta to the C-alpha-C bond. The incorporation of CH2 groups into the peptide backbone may thus drastically influence the backbone charge solvation preference. The characteristics of radical-driven beta-amino acid dissociation described herein are of particular importance to methods development, applications in peptide sequencing, and peptide and protein modification (e.g., deamidation and isomerization) analysis in life science research.