The mobile proton in polyalanine peptides.

Area of Science:

• Physical Chemistry
• Biophysical Chemistry
• Mass Spectrometry

Background:

• Polyalanine peptides exist in distinct helical and globule conformations.
• Understanding peptide conformational dynamics is crucial for protein folding and function.

Purpose of the Study:

• To investigate the temperature-dependent conformational changes of protonated polyalanine peptides using ion mobility.
• To determine the temperature at which proton mobility occurs within these peptides.
• To explore the relationship between peptide conformation and fragmentation patterns.

Main Methods:

• High-temperature ion mobility measurements using a drift tube.
• Analysis of conformational peak shifts and broadening as a function of temperature.
• Observation of peptide dissociation and fragmentation patterns.

Main Results:

• At room temperature, peptides exhibit distinct helix and globule peaks, which merge at higher temperatures, indicating rapid interconversion.
• Proton mobility is suggested to occur around 450 K due to intramolecular proton transfer during helix/globule transitions.
• Peptide fragmentation correlates with helical conformation, with helix formation facilitating dissociation by pooling protons at the C-terminus.

Conclusions:

• Protonated polyalanine peptides undergo temperature-induced conformational transitions and proton mobility.
• Helix formation in larger peptides promotes dissociation via proton pooling.
• An antiparallel helical dimer is observed and can be dissociated via collisional energy.