Solution Structure of Proline Pentapeptide. Analysis of the NOESY Spectra by Means of Spectrum Simulation

In this paper the NOESY spectra of proline pentapeptide are analyzed, and computer-simulated NOESY spectra are compared with the experimental spectra themselves. In simulating the spectra, the full relaxation matrix method is applied without assuming slow- or fast-motion limits. The calculated spectra are fitted to the experimental one in the following four steps: (1) determination of the proton-proton distance constraints from the experimental NOESY spectrum; (2) calculation of a rough 3D molecular structure by means of a distance geometry algorithm (DISGEO); (3) refinement of the structure; (4) adjustment of the correlation time of the overall tumbling motion of the molecule. The obtained proline pentapeptide structure in solution is close to the all-trans configuration of poly-L-prolines and the correlation time of the overall tumbling motion of the molecule is 0.4 ns; i.e. the isotropic rotational diffusion constant is D = 4.2 × 10⁸ s^-1.