CONFORMATIONAL STUDIES OF AN AMPHIPATHIC PEPTIDE CORRESPONDING TO HUMAN APOLIPOPROTEIN-A-II RESIDUES 18-30 WITH A C-TERMINAL LIPID-BINDING MOTIF EWLNS

A peptide was designed and synthesized to enhance the lipid binding pr operties of a 13-residue fragment of apolipoprotein A-II. The peptide, VTDYGKDLMEKVKEWLNS [apoA-II(18-30)+], contains a five-residue amphipa thic motif, EWLNS, at the C-terminus of apolipoprotein A-II residues 1 8-30. The lipid binding properties of apoA-II(18-30)+ were assessed us ing optical spectroscopy in the presence of sodium dodecyl sulfate (SD S), dodecylphosphocholine (DPC), tetradecyltrimethyl ammonium chloride (TMA) and dimyristoylphosphatidylcholine (DMPC). The fluorescence emi ssion spectra and the circular dichroism data suggested that apoA-II(1 8-30)+ interacted most strongly with SDS and most weakly with DMPC. An ensemble of structures for apoA-II(18-30)+ in aqueous solution contai ning SDS was calculated using distance geometry/simulated annealing me thods from 308 NOE-based distance restraints. The backbone (N-(CC)-C-a lpha=O) RMSD from the average structure of an ensemble of 15 out of 20 calculated structures was 0.54+/-0.16 Angstrom. Apart from some dynam ic fraying at both termini, the distance geometry and simulated anneal ing calculations showed that apoA-II(18-30) + adopted a well defined a mphipathic helix with distinct hydrophobic and hydrophilic faces. (C) Munksgaard 1996.