Three-dimensional structure determination of a uniformly labeled molecule by frequency-selective dipolar recoupling under magic-angle spinning

The complete three-dimensional (3D) structure of a glycylisoleucine (Gly-Il e) molecule was determined by individually measuring six dihedral angles wi th a frequency-selective homonuclear dipolar recoupling method, R2TR (rotat ional resonance in the tilted rotating frame), using a powder sample of dil uted uniformly 13,15-labeled Gly-Ile. Each dihedral angle was obtained by r ecoupling a dipolar interaction between three or four bonds distant spins c oncerned or observing a dipolar correlation 2D powder pattern. The 3D struc ture of a Gly-Ile molecule was also determined by X-ray crystallography, an d a good agreement with the NMR result was obtained. The results demonstrat e that the R2TR method in a uniformly labeled powder sample can provide the 3D structure without the need to prepare a lot of selectively labeled samp les.