The inclusion of peptoid monomers into antimicrobial peptides (AMPs) increases their proteolytic resistance, but introduces conformational flexibility (reduced hydrogen bonding ability and cis/trans isomerism). We here use NMR spectroscopy to answer how the insertion of a peptoid monomer influences the structure of a regular alpha-helical AMP upon interaction with a dodecyl phosphocholine (DPC) micelle. Insertion of [(2-methylpropyl) amino] acetic acid in maculatin-G15 shows that the structural change and conformational flexibility depends on the site of insertion. This is governed by the micelle interaction of the amphipathic helices flanking the peptoid monomer and the side chain properties of the peptoid and its preceding residue. (C) 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.