On the origin of NMR dipolar waves in transient helical elements of partially folded proteins.

The presence of dipolar coupling waves within helical elements of proteins implies an effective tilt of the main axis of the helical element relative to the magnetic field. Here, we investigate the origin of dipolar waves observed in helical elements of partially folded proteins. We find that the dipolar waves result from an effective tilt of the helix relative to the alignment axis that is determined by the directionality of the unfolded chains projected from the helix caps. The amplitude and phase of the dipolar wave depend in a predictable way on helix length, providing direct insight into helix stability, nucleation, and fraying in partially folded proteins.