How uniform is the peptide plane geometry? A high-accuracy NMR study of dipolar Cα-C′/HN-N cross-correlated relaxation
Vögeli, Beat
In: Journal of Biomolecular NMR, 2011, vol. 50, no. 4, p. 315-329
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- Highly precise and accurate measurements of very small NMR cross-correlated relaxation rates, namely those between protein HiN-Ni and Ci−1α-Ci−1′ dipoles, are demonstrated with an error of 0.03s−1 for GB3. Because the projection angles between the two dipole vectors are very close to the magic angle the rates range only from −0.2 to +0.2s−1. Small changes of the average vector orientations have a dramatic impact on the relative values. The rates suggest deviation from idealized peptide plane geometry caused by twists around the C′-N bonds and/or pyramidalization of the nitrogen atoms. A clear alternating pattern along the sequence is observed in β strands 1, 3 and 4 of GB3, where the side chains of almost all residues with large positive rates are solvent exposed. In the α helix all rates are relatively large and positive. Some of the currently most accurate structures of GB3 determined by both high resolution X-ray crystallography and NMR are in satisfactory agreement with the experimental rates in the helix and β strand 3, but not in the loops and the two central strands of the sheet for which no alternating pattern is predicted