Site-Resolved Determination of Peptide Torsion Angle phi from the Relative Orientations of Backbone N−H and C−H Bonds by Solid-State NMR

M. Hong, J. D. Gross, and R. G. Griffin*
Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
J. Phys. Chem. B, 1997, 101 (30), pp 5869–5874
DOI: 10.1021/jp970887u
Publication Date (Web): July 24, 1997
Copyright © 1997 American Chemical Society
*

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

Abstract

We describe a method for determining the torsion angle phi in peptides. The technique is based on the measurement of the relative orientation of the N−HN and Cα−Hα bonds, which is manifested in the rotational sideband spectrum of the sum and difference of the two corresponding dipolar couplings. The method exploits 15N−13C double-quantum and zero-quantum coherences, which evolve simultaneously under the N−H and C−H dipolar interactions. The magnitudes of these dipolar couplings scaled by the proton homonuclear decoupling sequence are directly extracted from control experiments that correlate the dipolar interactions with the isotropic chemical shifts. Applied to 15N-labeled N-acetyl-d,l-valine, the experiment yielded phi = −135°, which agrees well with the X-ray crystal structure. Simulations indicate that the accuracy of the measured angle phi is within ±10° when the N−HN and Cα−Hα bonds are approximately antiparallel and ±20° when they are roughly parallel. The technique is sufficiently sensitive to be applied to small peptides that are only labeled in 15N and to larger polypeptides that are uniformly and randomly labeled in both 15N and 13C. It allows phi angles in various residues to be measured simultaneously and resolved by the Cα chemical shifts.

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History

  • Published In Issue July 24, 1997
  • Received March 10, 1997
    Revised May 12, 1997

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