Insight into peptide self-assembly from anisotropic rotational diffusion derived from 13C NMR relaxation

The NMR heteronuclear relaxation rate's dependency on the anisotropy of rotational diffusion motions can be exploited to investigate the supramolecular organization that results from reversible peptide self-assembly in solution. The measurement of longitudinal (R-1) and transverse (R-2) C-13 relaxation rates for several peptide concentrations provides insight both into the orientation of individual molecules within the supramolecular assembly and its growth. The methodology was applied on the pore forming cyclic lipodepsipeptide pseudodesmin A, which reversibly assembles into supramolecular structures of indefinite size in non-polar organic solvents. The information extracted by correlating the C-13 R-1 and R-2 relaxation rates-obtained at natural abundance and at multiple peptide concentrations-with the orientation of the C-H bonds in the monomer conformation demonstrates the existence of an axially symmetric assembly that exhibits unidimensional growth upon increased peptide concentrations. The orientation of the pseudodesmin A peptide within this assembly could be determined accurately and is consistent with the suggested model for the pore forming function and the peptide-peptide interactions within the oligomer.