Conformational Study of Solid Polypeptides by 1H Combined Rotation and Multiple Pulse Spectroscopy NMR. 2. Amide Proton Chemical Shift

Abstract

The relationship between the amide proton chemical shift and the conformation of homopolypeptides in the solid state was studied using the 1H combined rotation and multiple pulse spectroscopy (CRAMPS) NMR method. The main-chain amide proton signals are considerably broad due to the residual dipolar couplings between the quadrupolar 14N nucleus and amide proton relative to other proton signals of solid polypeptides. We have prepared fully 15N-labeled (99 at. %) poly(l-alanines) ([Ala*]n) and poly(l-leucines) ([Leu*]n), adopting an α-helix or β-sheet form to eliminate the effect of the quadrupolar 14N nuclei, and then measured their 1H CRAMPS NMR spectra by increasing the magic-angle spinning speed. Thus, the 15NH proton chemical shifts of [Ala*]n and [Leu*]n were successfully determined to be 8.0−8.1 ppm (α-helix) and 8.6−9.1 ppm (β-sheet). Accordingly, it became apparent that the amide proton chemical shifts are sensitive to the conformation of solid polypeptides.