The helical conformations of 14- and 16-residue fragments of suzukacillin, a membrane channel-forming polypeptide

Abstract

The suzukacillin fragments, Boc-Ala-Aib-Aib-Gln-Aib-Leu-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-OMe (14), Boc-Ala-Aib-Ala-Aib-Aib-Gln-Aib-Leu-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-OMe (16G) and the completely apolar 16-residue peptide in which the glutamine residue has been replaced by alanine (16A) have been studied by 270 MHz ¹H-HMR, in C²HCl₃ and (C²H₃)₂SO solution. Intramolecularly hydrogen-bonded NH groups have been identified by temperature and solvent dependence of chemical shifts. Peptides 14 and 16A adopt folded 3₁₀ helical conformations stabilized by 11 and 13 hydrogen bonds, respectively. In peptide 16G there are 12 intramolecular hydrogen bonds, with the glycine NH being solvent-exposed, in contrast to 14 and 16A.