ISOTROPIC SOLUTIONS OF PHOSPHOLIPID BICELLES - A NEW MEMBRANE MIMETICFOR HIGH-RESOLUTION NMR-STUDIES OF POLYPEPTIDES

In order to illustrate the utility of phospholipid bicelles [Sanders, C.R. and Schwonek, J.P. (1992) Biochemistry, 31, 8898-8905] as a membr ane mimetic for high-resolution NMR studies, we have recorded two-dime nsional H-1 NMR spectra of the tetradecameric peptide mastoparan Vespu la lewisii in an isotropic aqueous solution of dimyristoyl and dihexan oyl phosphatidylcholine. Mastoparan is largely unstructured in water, but assumes a well-defined helical conformation in association with th e bilayers. A pronounced periodicity of the sequential NH chemical shi fts provides strong evidence that the helix axis of this short peptide is parallel, rather than perpendicular, to the bilayer plane. The bic ellar solutions still require in-depth morphological characterization, but they appear to be ideal media for NMR determination of the mode o f binding and the structure of membrane-associated peptides and protei ns.