The effect of fixed charge modifications on electron capture dissociation

Area of Science:

• Mass spectrometry
• Chemical physics
• Biochemistry

Background:

• Amyloid beta peptides are implicated in neurodegenerative diseases.
• Electron capture dissociation (ECD) is a powerful technique for peptide sequencing.
• The role of radicals in ECD fragmentation mechanisms is not fully understood.

Purpose of the Study:

• To investigate the influence of fixed charge tags on electron capture dissociation (ECD) of amyloid beta peptides.
• To elucidate the role of H* radicals and the free-radical cascade (FRC) mechanism in peptide ion fragmentation.
• To explore alternative dissociation pathways beyond H* transfer in ECD.

Main Methods:

• Electron capture dissociation (ECD) was performed on modified amyloid beta peptides (20-29 and 25-35).
• 2,4,6-Trimethylpyridinium (TMP) was used as a fixed charge tag to modulate radical behavior.
• Analysis of backbone and side-chain cleavages, and fragment ion abundances.

Main Results:

• Fixed charge tags significantly influenced backbone and side-chain cleavages in ECD.
• Increased number and proximity of charge tags generally reduced backbone cleavages and increased side-chain cleavages.
• Observation of c and z* ions in doubly labeled peptides suggests pathways beyond simple H* transfer.
• Internal fragment ions indicate the FRC mechanism is relevant for linear peptides too.

Conclusions:

• The number and location of fixed charge groups critically affect peptide fragmentation in ECD.
• H* transfer is important for NC(alpha) bond cleavage, but other radical migration pathways also exist.
• The free-radical cascade mechanism plays a role in the backbone cleavage of linear amyloid beta peptides during ECD.