Solution NMR structure of a D,L-alternating oligonorleucine as a model of beta-helix

beta -Helix structures are of particular interest due to their capacity to form transmembrane channels with different transport properties. However, t he relatively large number of beta -helices configurations does not allow a direct conformational analysis of beta -helical oligopeptides. A synthetic alternating D,L-oligopeptide with twelve norleucines (XIIMe) has been used as a model to get insight in the conformational features of beta -helix st ructures. The spatial configuration of XIIMe in solution has been determine d by NMR. An extensive set of distances (nuclear Overhauser effect) and dih edral (J coupling constants) constraints have been included in the molecula r dynamic calculations. The NMR experimental data and theoretical calculati ons clearly indicate that the XIIMe adopts a single beta (4.4)-helix-type c onformation in nonpolar solvents. (C) 2001 John Wiley & Sons, Inc.