Raman Microscopy Investigation of GLP-1 Peptide Association with Supported Phospholipid Bilayers

Area of Science:

• Biophysics
• Membrane Biology
• Spectroscopy

Background:

• Biological processes like cell signaling involve peptides interacting with membrane receptors.
• Glucagon-like peptide-1 (GLP-1) is a membrane-active incretin peptide crucial for biological functions.
• Understanding peptide-membrane interactions is key to deciphering cellular mechanisms.

Purpose of the Study:

• To adapt confocal Raman microscopy for quantifying unlabeled GLP-1 in supported phospholipid bilayers.
• To determine the equilibrium constant and maximum surface coverage of GLP-1 association with lipid bilayers.
• To investigate structural changes in the lipid bilayer upon GLP-1 intercalation.

Main Methods:

• Utilized confocal Raman microscopy to measure Raman scattering intensity of unlabeled GLP-1 relative to the lipid bilayer.
• Deposited supported phospholipid bilayers on the interior surfaces of wide-pore porous silica particles.
• Generated an adsorption isotherm by varying GLP-1 solution concentration to determine binding parameters.

Main Results:

• Quantified populations of unlabeled GLP-1 within supported phospholipid bilayers using Raman spectroscopy.
• Determined that maximum GLP-1 coverage is limited by bilayer accommodation, not peptide size.
• Observed structural changes in the bilayer, including increased acyl-chain order, upon GLP-1 intercalation.
• Found unlabeled GLP-1 has a 3-fold greater affinity for the lipid bilayer compared to fluorescently labeled GLP-1.

Conclusions:

• Confocal Raman microscopy is effective for quantifying unlabeled peptides in lipid bilayers.
• GLP-1 intercalation into lipid bilayers induces structural changes that facilitate accommodation.
• Fluorescent labeling can significantly alter the observed affinity of GLP-1 for lipid bilayers.