Association of the wasp venom peptide mastoparan with electrically neutral lipid vesicles. Salt effects on partitioning and conformational state.

We have measured circular dichroism signals of aqueous mastoparan and mastoparan-X when titrated with electrically neutral phospholipid unilamellar vesicles. The data could be converted into association isotherms (binding curves) under various conditions of salt content. In spite of the absence of a net charge in the lipid moiety, substantial salt effects have been observed regarding the partition coefficient of the peptide and its conformation in the associated state. These results are discussed on the basis of a general thermodynamic approach for peptide association with lipid bilayers.