Protegrin interaction with lipid monolayers: Grazing incidence X-ray diffraction and X-ray reflectivity study

Area of Science:

• Biophysics
• Materials Science
• Biochemistry

Background:

• Antimicrobial peptides (AMPs) are crucial for innate immunity.
• Understanding AMP-lipid interactions is key to developing new antimicrobial strategies.
• Phospholipid monolayers serve as model systems for cell membranes.

Purpose of the Study:

• To investigate the interactions of protegrin-1 (PG-1) with different phospholipid monolayers.
• To determine how PG-1 affects monolayer structure and packing.
• To elucidate the insertion mechanism of PG-1 into lipid bilayers.

Main Methods:

• Grazing incidence X-ray diffraction (GIXD) to study monolayer structure.
• Specular X-ray reflectivity (XR) to analyze film structure and peptide insertion.
• Formation of lipid A, dipalmitoyl-phosphatidylglycerol (DPPG), and dipalmitoyl-phosphatidylcholine (DPPC) monolayers.
• Experiments conducted under constant area conditions with varying surface pressures.

Main Results:

• PG-1 caused significant disruption of DPPG monolayers, indicated by the disappearance of Bragg peaks.
• PG-1 showed greater insertion into lipid A compared to DPPC at 20 mN/m.
• Peptide insertion decreased at higher surface pressures (30 mN/m).
• XR data confirmed PG-1 primarily inserts into the head group region of lipid monolayers.
• An additional adsorbed peptide layer was suggested for anionic lipids.

Conclusions:

• The extent of PG-1 interaction and monolayer disruption is dependent on lipid composition and packing density.
• PG-1's insertion behavior varies with the lipid head group and surface pressure.
• Anionic lipids may facilitate additional peptide adsorption below the head group layer.