Salt-Bridged Peptide Anion Gaseous Structures Enable Efficient Negative Ion Electron Capture Dissociation

Area of Science:

• Mass Spectrometry
• Analytical Chemistry
• Biochemistry

Background:

• Electron attachment to gaseous peptide anions enables novel tandem mass spectrometry (MS/MS) techniques.
• Negative ion electron capture dissociation (niECD) was proposed to require gaseous zwitterionic structures.
• Electron capture must occur at or be directed by a positively charged site.

Purpose of the Study:

• To further evaluate the zwitterion mechanism for niECD.
• To investigate the structural requirements for effective niECD.
• To assess the role of zwitterionic structures and salt-bridge formation in niECD efficiency.

Main Methods:

• Performing niECD on derivatized peptides designed to alter zwitterionic structure formation.
• Systematic study of synthetic peptides with varying zwitterion propensity.
• Traveling-wave ion mobility-mass spectrometry (TWIMS-MS) to analyze gas-phase structures.

Main Results:

• Introduction of fixed positive charges, guanidino, or sulfonate groups rescued niECD ability in refractory peptides.
• niECD efficiency decreased with decreasing zwitterion propensity across five peptide sets.
• TWIMS-MS revealed an inverse correlation between collision cross sections and niECD efficiency, indicating compact salt-bridged structures are necessary.

Conclusions:

• The zwitterion mechanism is strongly supported by the rescue of niECD ability through derivatization.
• Effective niECD requires both zwitterionic structures and compact, salt-bridged conformations in the gas phase.
• These findings provide critical insights into the structural prerequisites for niECD in peptide analysis.