Conformational backbone dynamics of the cyclic decapeptide antamanide. Application of a new multiconformational search algorithm based on NMR data.

A general procedure for the analysis of biomolecular structures by NMR in the presence of rapid conformational dynamics has been applied to the study of the cyclic decapeptide antamanide. Two-dimensional experiments, relaxation measurements in the rotating frame, and homo- and heteronuclear coupling constant determinations have been used to characterize the dynamic properties of the molecule, in combination with a novel search algorithm for investigating multiconformational equilibria. Direct evidence for the presence of a conformational exchange process with an activation energy of approximately 20 kJ mol-1 and an exchange lifetime of approximately 25 microseconds at 320 K has been obtained from rotating frame relaxation measurements. This evidence is combined with the information derived from the multiconformational search algorithm MEDUSA to propose sets of structures that coexist in a dynamic exchange equilibrium.