Alpha-helical hydrophobic polypeptides form proton-selective channels in lipid bilayers

Area of Science:

• Biophysics
• Membrane Biology
• Biochemistry

Background:

• Proton translocation is vital for cellular energy processes but its mechanism is not fully understood.
• Hydrophobic alpha-helices are theorized to facilitate ion transport across lipid bilayers.

Purpose of the Study:

• To investigate if hydrophobic alpha-helices, specifically polyamino acids, can form low-energy pathways for proton translocation.
• To model functional proton channels found in biological membranes.

Main Methods:

• Incorporation of polyamino acids (poly-L-alanine, poly-L-leucine) into liposomes and planar lipid membranes.
• Measurement of proton and potassium permeability coefficients.
• Analysis of lipid and amino acid content.
• Fourier transform infrared spectroscopy to determine peptide conformation.
• Single-channel recording to assess conductive events.

Main Results:

• Long-chain poly-L-alanine and poly-L-leucine significantly increased liposome proton permeability (5-7 fold) without affecting potassium permeability.
• Planar lipid membranes with these polyamino acids showed a 10-30 fold increase in proton-conducting events.
• Poly-L-leucine exhibited higher conductivity than poly-L-alanine due to larger event amplitudes and frequencies.
• Channel-like activity demonstrated switching between conductive and non-conductive states.

Conclusions:

• Hydrophobic polyamino acids form proton-conducting defects in lipid bilayers.
• These findings support the hypothesis that alpha-helical bundles can facilitate proton translocation.
• The study provides a model for understanding proton channel function in biological systems.