73 research outputs found
The combination of electron capture dissociation and fixed charge derivatization increases sequence coverage for O-glycosylated and O-phosphorylated peptides
Hydrogen Bonding Constrains Free Radical Reaction Dynamics at Serine and Threonine Residues in Peptides
Free radical-initiated peptide sequencing (FRIPS) mass spectrometry derives advantage from the introduction of highly selective low-energy dissociation pathways in target peptides. An acetyl radical, formed at the peptide N-terminus via collisional activation and subsequent dissociation of a covalently attached radical precursor, abstracts a hydrogen atom from diverse sites on the peptide, yielding sequence information through backbone cleavage as well as side-chain loss. Unique free-radical-initiated dissociation pathways observed at serine and threonine residues lead to cleavage of the neighboring N-terminal C_α–C or N–C_α bond rather than the typical Cα–C bond cleavage observed with other amino acids. These reactions were investigated by FRIPS of model peptides of the form AARAAAXAA, where X is the amino acid of interest. In combination with density functional theory (DFT) calculations, the experiments indicate the strong influence of hydrogen bonding at serine or threonine on the observed free radical chemistry. Hydrogen bonding of the side-chain hydroxyl group with a backbone carbonyl oxygen aligns the singly occupied π orbital on the β-carbon and the N–C_α bond, leading to low-barrier β-cleavage of the N–C_α bond. Interaction with the N-terminal carbonyl favors a hydrogen-atom transfer process to yield stable c and z• ions, whereas C-terminal interaction leads to effective cleavage of the C_α–C bond through rapid loss of isocyanic acid. Dissociation of the C_α–C bond may also occur via water loss followed by β-cleavage from a nitrogen-centered radical. These competitive dissociation pathways from a single residue illustrate the sensitivity of gas-phase free radical chemistry to subtle factors such as hydrogen bonding that affect the potential energy surface for these low-barrier processes
Electron capture in spin-trap capped peptides. An experimental example of ergodic dissociation in peptide cation-radicals
On the survival of peptide cations after electron capture: Role of internal hydrogen bonding and microsolvation
Comparative dissociation of peptide polyanions by electron impact and photo-induced electron detachment
Hydrogen Bonding Constrains Free Radical Reaction Dynamics at Serine and Threonine Residues in Peptides
Electron capture in charge-tagged peptides. Evidence for the role of excited electronic states
Nonergodicity in electron capture dissociation investigated using hydrated ion nanocalorimetry
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