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 Cn2H(2n+1)CO-L-Phe-D-Oxd-OBn or Cn2H(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 2H NMR. The peptide backbone showed 13C NMR chemical shifts in agreement with -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 pre¬sence of synthetic POPC bilayers. Two different molecular species were detected under these circumstan¬ces: (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 aggre¬gates. 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.