Changes in Calmodulin Main-Chain Dynamics upon Ligand Binding Revealed by Cross-Correlated NMR Relaxation Measurements Tianzhi Wang Kendra King Frederick Tatyana I. Igumenova A. Joshua Wand Erik R. P. Zuiderweg 10.1021/ja045743p.s001 https://acs.figshare.com/articles/journal_contribution/Changes_in_Calmodulin_Main_Chain_Dynamics_upon_Ligand_Binding_Revealed_by_Cross_Correlated_NMR_Relaxation_Measurements/3303340 The fast dynamics of protein backbones are often investigated by nuclear magnetic relaxation experiments that report on the degree of spatial restriction of the amide bond vector. By comparing calmodulin in the peptide-bound and peptide-free states with these classical methods, we observe little difference in the dynamics of the polypeptide main chain (average order parameter decrease of 0.01 unit upon binding). However, when using NMR methods that monitor the mobility of the CO−Cα bond vector, we reveal a significant reduction of dynamics of the protein main chain (average order parameter decrease of 0.048 units). Previous investigations have suggested that the side-chain dynamics is reduced by an average of 0.07 order parameter units upon ligand binding (Lee, A. L.; Kinnear, S. A.; Wand, A. J. <i>Nat. Struct. Biol.</i> <b>2000</b>, <i>7</i>, 72−77). The current findings suggest that the change of the CO−Cα bond vector dynamics is intermediate between the changes in NH and side-chain dynamics and report a previously undetected loss of main-chain entropy. Weak site-to-site correlations between the different motional indicators are also observed. 2005-01-26 00:00:00 dynamic 0.07 order parameter units ligand binding relaxation experiments Previous investigations 0.048 units 0.01 unit NH order parameter decrease CO Ligand Binding Revealed protein backbones amide bond vector NMR methods