The Complexity of Protein Energy Landscapes Studied by Solution NMR Relaxation Dispersion Experiments.
Related Articles The Complexity of Protein Energy Landscapes Studied by Solution NMR Relaxation Dispersion Experiments.
J Phys Chem B. 2015 Feb 13;
Authors: Khirich G, Loria JP
Abstract
The millisecond timescale motions in ribonuclease A (RNase A) were studied by solution NMR CPMG and off-resonance R1? relaxation dispersion experiments over a wide pH and temperature range. These experiments identify three separate protein regions termed Cluster 1, Cluster 2, and R33 whose motions are governed by distinct thermodynamic parameters. Moreover each of these regions has motions with different pH dependencies. Cluster 1 shows an increase in activation enthalpy and activation entropy as the pH is lowered, whereas Cluster two exhibits the opposite behavior. In contrast the activation enthalpy and entropy of R33 show no pH dependence. Compounding the differences, ?? values for Cluster 2 are characteristic of two-site conformational exchange yet similar analysis for Cluster 1 indicates that this region of the enzyme exhibits conformational fluctuations between a major conformer and a pH-dependent average of protonated and de-protonated minor conformers.
PMID: 25680027 [PubMed - as supplied by publisher]
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