title: Lipid binding interactions of antimicrobial plant seed defence proteins: puroindoline-a and β-purothionin.
abstract: The indolines and thionins are basic, amphiphilic and cysteine-rich proteins found in cereals; puroindoline-a (Pin-a) and β-purothionin (β-Pth) are members of these families in wheat (Triticum aestivum). Pin-a and β-Pth have been suggested to play a significant role in seed defence against microbial pathogens, making the interaction of these proteins with model bacterial membranes an area of potential interest. We have examined the binding of these proteins to lipid monolayers composed of 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG) using a combination of neutron reflectometry, Brewster angle microscopy, and infrared spectroscopy. Results showed that both Pin-a and β-Pth interact strongly with condensed phase DPPG monolayers, but the degree of penetration was different. β-Pth was shown to penetrate the lipid acyl chain region of the monolayer and remove lipids from the air/liquid interface during the adsorption process, suggesting this protein may be able to both form membrane spanning ion channels and remove membrane phospholipids in its lytic activity. Conversely, Pin-a was shown to interact mainly with the head-group region of the condensed phase DPPG monolayer and form a 33 Å thick layer below the lipid film. The differences between the interfacial structures formed by these two proteins may be related to the differing composition of the Pin-a and β-Pth hydrophobic regions.
authors.affiliation: ISIS Spallation Neutron Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 OQX, UK. luke.clifton@stfc.ac.uk
authors.forename: Luke A
authors.initials: LA
authors.lastname: Clifton
authors.forename: Michael R
authors.initials: MR
authors.lastname: Sanders
authors.forename: Arwel V
authors.initials: AV
authors.lastname: Hughes
authors.forename: Cameron
authors.initials: C
authors.lastname: Neylon
authors.forename: Richard A
authors.initials: RA
authors.lastname: Frazier
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Green
mesh_terms: D000595:Amino Acid Sequence; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010715:Phosphatidylglycerols / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D012639:Seeds / Q000378:metabolism* / Q000382:microbiology; D014908:Triticum / Q000378:metabolism* / Q000382:microbiology
chemical_list: D023181:Antimicrobial Cationic Peptides; D010715:Phosphatidylglycerols; D010940:Plant Proteins; C082942:puroindoline protein, Triticum aestivum; C016085:purothionin; C030345:1,2-dipalmitoylphosphatidylglycerol