Efficient determination of angles subtended by Cα-Hα and N-HN vectors in proteins via dipole-dipole cross-correlation§

The angle ΘCαHα,NHN subtended by the internuclear vectors 13Cα-Hα and 15N-HN in doubly-labeled proteins can be determined by observing the effect of cross-correlation between the dipolar interactions on zero- and double-quantum coherences involving 13Cα and 15N. Two complementary 2D experiments with the appearance of 15N-HN correlation spectra yield signal intensities that depend on the rate of interconversion through cross-correlated relaxation of in-phase and doubly antiphase zero- and double-quantum coherences. The ratio of the signal intensities in the two experiments bears a simple relationship to the cross-correlation rate, and hence to the angle ΘCαHα,NHN. Assuming planarity of the peptide bond, the dihedral angle Ψ (between Cα and C′) can be determined from the knowledge of ΘCαHα,NHN. The experiments are very time-effective and provide good sensitivity and excellent spectral resolution.