Biophys J, October 2002, p. 2074-2083, Vol. 83, No. 4

Interaction between -Purothionin and Dimyristoylphosphatidylglycerol: A ³¹P-NMR and Infrared Spectroscopic Study

Julie-Andrée Richard,^* Isabelle Kelly,^* Didier Marion, Michel Pézolet,^* and Michèle Auger^*

 ^*Département de Chimie, Centre de Recherche en Sciences et Ingénierie des Macromolécules, Université Laval, Québec G1K 7P4, Canada; and  Institut National de la Recherche Agronomique, Laboratoire de Biochimie et Technologie des Protéines, 44316 Nantes Cedex 03, France

The interaction of -purothionin, a small basic and antimicrobial protein from the endosperm of wheat seeds, with multilamellar vesicles of dimyristoylphosphatidylglycerol (DMPG) was investigated by ³¹P solid-state NMR and infrared spectroscopy. NMR was used to study the organization and dynamics of DMPG in the absence and presence of -purothionin. The results indicate that -purothionin does not induce the formation of nonlamellar phases in DMPG. Two-dimensional exchange spectroscopy shows that -purothionin decreases the lateral diffusion of DMPG in the fluid phase. Infrared spectroscopy was used to investigate the perturbations, induced by -purothionin, of the polar and nonpolar regions of the phospholipid bilayers. At low concentration of -purothionin, the temperature of the gel-to-fluid phase transition of DMPG increases from 24°C to ~33°C, in agreement with the formation of electrostatic interactions between the cationic protein and the anionic phospholipid. At higher protein concentration, the lipid transition is slightly shifted toward lower temperature and a second transition is observed below 20°C, suggesting an insertion of the protein in the hydrophobic core of the lipid bilayer. The results also suggest that the presence of -purothionin significantly modifies the lipid packing at the surface of the bilayer to increase the accessibility of water molecules in the interfacial region. Finally, orientation measurements indicate that the -helices and the -sheet of -purothionin have tilt angles of ~60° and 30°, respectively, relative to the normal of the ATR crystal.

Biophys J, October 2002, p. 2074-2083, Vol. 83, No. 4
© 2002 by the Biophysical Society   0006-3495/02/10/2074/10  $2.00