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Leveraging Electron Transfer Dissociation for Site Selective Radical Generation: Applications for Peptide Epimer
Yana A Lyon1, Gregory Beran1, Ryan R Julian2
1Department of Chemistry, University of California-Riverside, 501 Big Springs Road, Riverside, CA, 92521, USA.
Journal of the American Society for Mass Spectrometry
|April 5, 2017
Summary
A new electron-transfer dissociation (ETD) method uses electronic excitation to cleave carbon-iodine bonds, enabling novel peptide fragmentation. This pathway aids in identifying peptide isomers and epimers without lasers.
Area of Science:
- Mass Spectrometry
- Analytical Chemistry
- Chemical Physics
Background:
- Traditional electron-transfer dissociation (ETD) produces c/z ions, side-chain losses, and disulfide bond scission via complex fragmentation pathways.
- Photodissociation experiments have previously utilized homolytic cleavage of carbon-iodine bonds.
Purpose of the Study:
- To report a novel dissociation pathway in ETD involving homolytic cleavage of carbon-iodine bonds.
- To explore the utility of this pathway for peptide analysis, particularly isomer and epimer identification.
Main Methods:
- Utilizing electronic excitation in ETD experiments to induce homolytic cleavage of carbon-iodine bonds.
- Observing loss of iodine and hydrogen iodide (HI) as primary fragmentation events.
- Employing additional collisional activation to enhance HI loss and radical-directed dissociation.
Main Results:
- A novel ETD pathway yielding homolytic carbon-iodine bond cleavage was discovered, distinct from traditional ETD fragmentation.
- Both loss of iodine and loss of hydrogen iodide (HI) were observed.
- Collisional activation significantly enhanced HI loss, suggesting a role for arginine side chains in electron storage and peptide radical formation.
- Radical-directed dissociation was observed after collisional activation of HI loss products, proving useful for isomer and epimer identification.
Conclusions:
- The novel ETD pathway offers a laser-free alternative to photodissociation for cleaving carbon-iodine bonds.
- This method provides a new tool for detailed peptide analysis, including the differentiation of isomers and epimers.
- The mechanism likely involves electron storage in the arginine side chain, leading to peptide radical formation and subsequent dissociation.