Protein dynamical transition does not require protein structure

Terahertz time domain spectroscopy shows that the protein dynamical transition, the rapid increase in protein dynamics occurring at ∼200K, needs neither tertiary nor secondary structure. Further, short chain alanine studies find a dynamical transition down to penta-alanine, with no transition observed for di-alanine or tri-alanine. These results reveal the temperature dependence arises strictly from the side-chain interaction with the solvent. The lack of a transition for shorter chain peptides may indicate a qualitative change in this interaction occurs at a specific peptide chain length.