Dynamical Transition of Collective Motions in Dry Proteins

The effects of pressure on the energy landscape of proteins

“…This phenomenon is usually referred to as Protein Dynamical Transition (PDT) 4 . The physical origin of the PDT and its relationship with the dynamical properties of hydration water and/or the external matrix, has raised debates in the literature, still being an open and intriguing question 2 , 4 – 16 . The motions arising above the PDT, which are specific for proteins, are believed to be important for functionality, since they give to protein molecules the flexibility which is necessary to perform their functions 1 .…”

“…Since hydrogen atoms make up about half the atoms in a protein and are almost uniformly distributed within the molecule, this technique gives a global view of protein motions 35 . Only very recently, a dynamical transition, not present for hydrogen atoms, has been observed for the backbone atoms in an extremely dry per-deuterated protein sample 16 . On the contrary, for hydrated proteins, as it is in our sample, when the dynamical properties of non-exchangeable hydrogen atoms are compared to those of backbone atoms 36 or of all atoms of the molecules 35 , 37 , analogous results are generally obtained.…”

Dynamical properties of myoglobin in an ultraviscous water-glycerol solvent investigated with elastic neutron scattering and FTIR spectroscopy

“…On this basis, a comparison of ENS data with techniques able to probe the structural and dynamical properties of protein's backbone atoms, as FTIR in the amide region, is highly desirable also in view of very recent results indicating that in some cases the backbone atoms may behave differently from hydrogen atoms of the side chains, with respect to the PDT. In particular, in extremely dry proteins heavy backbone atoms seem to display a dynamical transition at~180-200 K, which is usually absent when non-exchangeable hydrogen atoms are the main contributors to the observed signal [31]. In fact, in this last case, a much larger hydration (h~0.1-0.2) is required to observe the dynamical transition [17].…”

“…Future work will verify whether this is a general conclusion or if different experimental conditions (e.g. extremely dry samples) can be found in which a decoupling is observed, as recently suggested [31]. …”

“…In view of the above considerations, it would be highly desirable to investigate the PDT on suitable protein samples with the aim of comparing the thermal dependence of the MSD of non-exchangeable hydrogen atoms, as obtained by ENS, with other measurable quantities related to the dynamic properties of backbone atoms. This can be of particular interest also in view of the fact that it has been very recently reported that protein backbone atoms may display different dynamical properties with respect to side chains hydrogen atoms [31].…”