Onsets of anharmonicity in protein dynamics

Two onsets of anharmonicity are observed in the dynamics of the protein lysozyme. One at T similar to 100 K appears in all samples regardless of hydration level and is consistent with methyl group rotation. The second, the well-known dynamical transition at T similar to 200-230 K, is only observed at a hydration level h greater than similar to 0.2 and is ascribed to the activation of an additional relaxation process. Its variation with hydration correlates well with variations of catalytic activity suggesting that the relaxation process is directly related to the activation of modes required for protein function.