Journal Highlight: Interpretation of seemingly contradictory data: Low NMR S2 order parameters observed in helices and high NMR S2 order parameters in disordered loops of the protein hGH at low pH

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  • Published: Jul 31, 2017
  • Author: spectroscopyNOW
  • Channels: NMR Knowledge Base
thumbnail image: Journal Highlight: Interpretation of seemingly contradictory data: Low NMR <em>S</em><sup>2</sup> order parameters observed in helices and high NMR <em>S</em><sup>2</sup> order parameters in disordered loops of the protein hGH at low pH

S2 order parameter-restraining MD simulations have been used to explain the contradictory S2 order parameters for backbone N−H vectors derived from NMR relaxation measurements on hGH at low pH.

Interpretation of seemingly contradictory data: Low NMR S2 order parameters observed in helices and high NMR S2 order parameters in disordered loops of the protein hGH at low pH

Chemistry - A European Journal, 2017, 23, 9585-9591
Lorna J. Smith, Roya Athill, Wilfred F. van Gunsteren and Niels Hansen

Abstract: At low pH, human growth hormone (hGH) adopts a partially folded state, in which the native helices are maintained, but the long loop regions and side-chain packing become disordered. Some of the S2 order parameters for backbone N−H vectors derived from NMR relaxation measurements on hGH at low pH initially seem contradictory. Three isolated residues (15, 20, and 171) in helices A and D exhibit low order parameter values (<0.5) indicating flexibility, whereas residue 143 in the centre of a long flexible loop region has a high order parameter (0.82). Using S2 order parameter restraining MD simulations, this paradox has been resolved. Low S2 values in helices are due to the presence of a mixture of 310-helical and α-helical hydrogen bonds. High S2 values in relatively disordered parts of a protein may be due to fluctuating networks of hydrogen bonds between the backbone and the side chains, which restrict the motion of N−H bond vectors.

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