Modification of phospholipid membrane structure by the plant toxic peptide Pyrularia thionin.

Pyrularia thionin (P thionin) is a bioactive peptide from the parasitic plant Pyrularia pubera. The structural aspects of its interaction with phospholipid membranes were investigated by measuring the responses of phosphorescence quenching, EPR spin labels, and 1H and 31P NMR at different phospholipid compositions. In phosphatidylcholine bilayers containing cardiolipin or phosphatidylinositol, P thionin induced a pronounced increase in the membrane viscosity, and at higher P thionin concentrations the formation of nonbilayer structures was observed. In phosphatidylcholine bilayers containing phosphatidylserine, P thionin induced a significant transformation of membrane lamellar structure accompanied by a decrease of membrane viscosity. In all investigated lipid systems added P thionin caused an increase in membrane permeability and induced a fusion of sonicated liposomes. The specificity of P thionin interaction with phosphatidylserine-containing membrane is discussed and a model of phospholipid membrane modification by P thionin is suggested.