Analysis of peptide rotational diffusion by homonuclear NMR

The analysis of the rotational diffusion of a molecule using homonuclear NMR is investigated. The homonuclear longitudinal and transverse cross-relaxation rates, which can be quantitatively measured using off-Resonance Rotating frame nuclear Overhauser Effect Spectroscopy (ROESY), are used to build a distribution, which exhibits a solid-state-like pattern characteristic of the diffusion tensor. The distributions of the antimicrobial peptide ranalexin in water and in 30% of trifluoracetic acid (TFE) are compared, and the peptide rotational diffusion is shown to be more isotropic in water than in 30% TFE. This difference is further supported by the analysis of NMR ranalexin conformers in 30% TFE, and by the analysis of a molecular dynamics simulation of peptide in water.