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    The role of protein hydrophobicity in thionin–phospholipid interactions: a comparison of α1 and α2-purothionin adsorbed anionic phospholipid monolayers

    Year: 2012

    Journal: Phys. Chem. Chem. Phys., 2012, 14 (39), 13569-13579, 20131009

    Authors: Luke A. Clifton, Michael Sanders, Christian Kinane, Tom Arnold, Karen J. Edler, Cameron Neylon, Rebecca J. Green, Richard A. Frazier

    Organizations: ISIS Spallation Neutron Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxfordshire, UK; Reading School of Pharmacy, University of Reading, PO Box 226, Whiteknights, Reading, UK; Department of Food and Nutritional Sciences, University of Reading, PO Box 226, Whiteknights, Reading, UK; Diamond Light Source, Diamond house, Harwell Science and Innovation Campus, Didcot, Oxfordshire, UK; Department of Chemistry, University of Bath, Bath, UK

    The plant defence proteins α1- and α2-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 α1- and α2-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 α1 and α2-Pth interact strongly with condensed phase 1,2-dipalmitoyl-sn-glycero-3-phospho-(1′-rac-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 α2-Pth showed faster disruption of the lipid film and removed more phospholipid (12%) from the interface than α1-Pth. Correlating the protein properties and lipid binding activity suggests that hydrophobicity plays a key role in the membrane lipid removal activity of thionins.