Site-Specific Peptide Probes Detect Buried Water in a Lipid Membrane

Area of Science:

• Biophysics
• Membrane protein structure and dynamics
• Spectroscopy

Background:

• Transmembrane peptides possess polar residues that may influence the membrane's electrostatic environment and promote hydration.
• Understanding peptide hydration within the membrane core is crucial for elucidating membrane transport mechanisms.

Purpose of the Study:

• To develop and apply a nonperturbative method for probing peptide backbone hydration at specific depths within a lipid bilayer.
• To investigate the hydration environment of an amphiphilic pH-low insertion peptide within a membrane model.

Main Methods:

• Utilized site-specific isotope labeling to tag peptide backbone atoms.
• Employed ultrafast two-dimensional infrared (2D IR) spectroscopy to detect subtle changes in peptide hydration.
• Integrated spectral modeling with molecular dynamics (MD) simulations for in-depth analysis of spectroscopic data.

Main Results:

• The pH-low insertion peptide exists in a heterogeneous environment within the membrane.
• Significant backbone hydration was observed for nonpolar residues adjacent to charged residues.
• A leucine residue, 1 nm into the hydrophobic core, showed up to ~20% hydrogen-bonded populations, indicating substantial water interaction.

Conclusions:

• The study presents a novel strategy for mapping hydration within transmembrane peptides.
• Polar residues within transmembrane peptides can facilitate water molecule transport into the hydrophobic membrane core.
• These findings have implications for understanding water permeation and peptide behavior in biological membranes.