Membrane Interactions Drive Hydrogen-Bond Dynamics in the pH-Low Insertion Peptide (pHLIP)

Area of Science:

• Biophysics
• Chemical Physics
• Molecular Biology

Background:

• The pH Low Insertion Peptide (pHLIP) is a model for studying peptide-membrane interactions.
• Intermediate structures of pHLIP during folding and insertion are poorly understood.
• The relationship between environment, membrane interactions, and local dynamics needs characterization.

Purpose of the Study:

• Investigate pHLIP's secondary structure and local environments during pH-induced membrane insertion.
• Characterize intermediate states and dynamics of pHLIP in phospholipid bilayers.
• Elucidate the relationship between environmental factors and pHLIP's structural dynamics.

Main Methods:

• Ultrafast two-dimensional infrared (2D IR) spectroscopy to probe structure and H-bond dynamics.
• Amide I 2D IR spectroscopy for peptide backbone analysis.
• Molecular dynamics (MD) simulations for detailed structural and dynamic insights.

Main Results:

• A dynamic shift in pHLIP occurs between pH 6.5 and 6.0.
• The alpha-helical transition happens between pH 6.0 and 5.8, above the insertion pH.
• Faster dynamics during the transition suggest hydrogen bond network disruptions.

Conclusions:

• The findings support a 'fold-then-insert' mechanism for pHLIP.
• pHLIP's structural transitions are pH-dependent and distinct from insertion.
• Understanding these dynamics provides insight into peptide-membrane interactions.