AnaIysis of dynamic behavior of ribonuclease upon ligand binding using high resolution NMR

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The idea that the internal motions in enzymes were restricted upon ligand binding has been accepted. Recently, it was reported that internal motions in some enzymes such 4-oxalocrotonate tautomerase, hen and human lysozymes increased upon ligand binding. Now, it is controversial whether internal motions in enzymes increase or not upon ligand binding. Therefore, in this research, in order elucidate whether the increased internal motions in enzymes upon binding its ligand is in general or not, we prepared ^<15>N uniformly labeled ribonuclease T1 from Pichia pastoris and measured the relaxation time (T_1 and T_2) of nitrogen atoms and NOEs between ^1H and ^<15>N in them in the presence or absence of 3'-GMP. Order parameters in every residues of ^<15>N uniformly labeled ribonuclease T1 was calculated by model free analysis, of the relaxation time (T_1 and T_2) of nitrogen atoms and NOEs between ^1H and ^<15>N. As the results, it was elucidated that some residues in ribonuclease T1 had the smaller order parameters, indicating that the internal motions in ribonuclease T1 molecule increased upon binding its ligand.