The interaction of lipid modified pseudopeptides with lipid membranes.

We have studied the structure of two lipopeptides based on the simple dipeptide building block L-Phe-D-Oxd. These peptides have been reported previously to form fiber-like materials. The lipopeptides synthesized here had the structures C(n)(2)H((2n+1))CO-L-Phe-D-Oxd-OBn or C(n)(2)H((2n+1))CO-D-Phe-L-Oxd-OBn with n = 5 or 11. Addition of the N-terminal lipid modification did not cause a major disturbance of the structures these molecules form. The lipid modifications themselves showed highly rigid structures as inferred from solid-state (2)H NMR. The peptide backbone showed (13)C NMR chemical shifts in agreement with β-sheet secondary structure. Addition of a lipid modification to the N-terminus is a common motif in biology to attach proteins to the membrane. Therefore, we also investigated the lipopeptides in the presence of synthetic POPC bilayers. Two different molecular species were detected under these circumstances: (i) lipopeptide monomers that showed chain order parameters similar to those of the host membrane, (ii) lipopeptide aggregates that exhibited very similar structures and dynamics as the crystalline aggregates. Overall, the lipopeptides showed a well defined and rigid secondary structure that is in agreement with fibrillar aggregates previously detected for those peptides without the lipid modification.