The Protein Dynamical Transition Does Not Require the Protein Polypeptide Chain

We give experimental evidence that the main features of protein native protein dynamics revealed by neutron scattering, i.e., the protein dynamical transition and the boson peak, do not need the protein polypeptide chain. We show that a rapid increase of hydrogen atoms fluctuations at about 220 K, analogous to the one observed in hydrated myoglobin powders, is also observed in a hydrated amino acids mixture with the chemical composition of myoglobin but lacking the polypeptide chain; in agreement; with the protein behavior, the transition is abolished in the dry mixture. Further, an, excess of low-frequency vibrational modes around 3 meV, typically observed in protein ' powders, is also observed in our mixture.. Our results confirm that the dynamical, transition is a water-driven onset and indicate that it mainly involves the amino acid side, chains. Taking together the present data and recent results on the dynamics of a protein, in denatured conformation and on the activity of dehydrated proteins, it can be I concluded that the protein dynamical transition is neither a necessary nor a sufficient condition for active protein conformation and function.