Plant Seed Defence Proteins : Solution Structure and Lipid Binding Studies
L. A. Clifton1, R. J. Green2, and R.A. Frazier3
1
ISIS Spallation Neutron Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory,
Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 OQX, UK
2
Reading School of Pharmacy, University of Reading, PO Box 226, Whiteknights, Reading, RG6 6AP, UK
3
Department of Food and Nutritional Sciences, University of Reading, PO Box 226, Whiteknights, Reading,
RG6 6AP, UK
[email protected]
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. The antibacterial and antifungal activity of these
proteins is thought to be related to their ability to interact directly with the lipid components
of the pathogen membrane. Using a combination of interfacial and solution analysis
techniques we have shown how size, binding region composition and charge effect the
relative interaction of these proteins with phospholipid monolayer1 and bilayer membrane
models. Furthermore, we have shown that Pin-a forms large (~38 monomer) oligomicelles2,
revealing surfactant-like behaviour that is not exhibited for other indolines or thionins and is
attributed to the protein’s tryptophan-rich lipid binding domain. The findings of these studies
have implications in our understanding of the biochemical mechanism of wheat endosperm
texturing (a quality trait by wheat flour is classified) and plant seed defence, as well as
suggesting potential applications for the proteins as topical antibiotics.
+β-Pth
+β-Pth
+Pin-a
W
W
+Pin-a
Micelle
40.4 Å
W
12.6 Å
W
W
W
W
W
W
W
W
W
+Pin-a
W
W
+Pin-a
W
W
W
+β-Pth
β-Purothionin
W
+Pin-a
W
+β-Pth
W
W
+β-Pth
112 Å
W
W
W
+β-Pth
W
W
W
W
W
W
W
W
+Pin-a
W
W
Puroindoline-a
Monomer
W
<16.7 Å
References
1. Clifton L. A., Green R. J., Hughes A. V., and Frazier R. A., J. Phys, Interfacial Structure of Wild-Type and Mutant
Forms of Puroindoline-b Bound to DPPG Monolayers, J. Phys. Chem. B 2008, 112, 15907–15913.
2. Clifton, L. A., Sanders M. R., Castelletto, V., Rogers S. E., Heenan R. K., Neylon C., Frazier, R. A, and Green, R. J.
Puroindoline-a, a Lipid Binding Protein from Common Wheat, Spontaneously Forms Prolate Protein Micelles in
Solution, Phys. Chem. Chem. Phys., 2011, 13, 8881-8888.