The role of protein hydrophobicity in thionin-phospholipid interactions: a comparison of alpha 1 and alpha 2-purothionin adsorbed anionic phospholipid monolayers

• Published in: Physical chemistry chemical physics : PCCP Vol. 14; no. 39; pp. 13569 - 13579
• Main Authors: Clifton, Luke A, Sanders, Michael, Kinane, Christian, Arnold, Tom, Edler, Karen J, Neylon, Cameron, Green, Rebecca J, Frazier, Richard A
• Format: Journal Article
• Language: English
• Published: 01.09.2012
• Subjects: Binding; Charge; Hydrophobicity; Lipids; Monolayers; Peptides; Phospholipids; Proteins
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c2cp42029e

The plant defence proteins alpha 1- and alpha 2-purothionin (Pth) are type 1 thionins from common wheat (Triticum aestivum). These highly homologous proteins possess characteristics common amongst antimicrobial peptides and proteins, that is, cationic charge, amphiphilicity and hydrophobicity. Both alpha 1- and alpha 2-Pth possess the same net charge, but differ in relative hydrophobicity as determined by C18 reversed phase HPLC. Brewster angle microscopy, X-ray and neutron reflectometry, external reflection FTIR and associated surface pressure measurements demonstrated that alpha 1 and alpha 2-Pth interact strongly with condensed phase 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-ra c-glycerol) (DPPG) monolayers at the air/liquid interface. Both thionins disrupted the in-plane structure of the anionic phospholipid monolayers, removing lipid during this process and both penetrated the lipid monolayer in addition to adsorbing as a single protein layer to the lipid head-group. However, analysis of the interfacial structures revealed that the alpha 2-Pth showed faster disruption of the lipid film and removed more phospholipid (12%) from the interface than alpha 1-Pth. Correlating the protein properties and lipid binding activity suggests that hydrophobicity plays a key role in the membrane lipid removal activity of thionins.