Characterisation of the Interactions of Aromatic Amino Acids with Diacetyl Phosphatidylcholine

Abstract

A simple bimolecular system for characterising the interactions of amino acids with diacyl-3-phosphatidylcholines has been developed. The system contains two components: an N-acetyl amino acid N'-alkyl amide and diacetyl-3-sn-phosphatidylcholine (DAPC). Interactions between a series of aromatic amino acids and DAPC have been characterised by H-1 NMR techniques. Of the amino acids examined, tryptophan and tyrosine were shown to have particularly favourable interactions with the DAPC choline headgroup. Our observations are consistent with the previously reported tendency for these amino acids to occur preferentially at the lipid-water interface. Using data from ROESY experiments and complexation-induced chemical shift changes, we have been able to generate molecular models for the tryptophan-DAPC adduct that are consistent with the observed results. The adduct is characterised by amide carbonyl-cation interactions, hydrogen bonding and cation-pi interactions.