Comment on "Puzzle of the protein dynamical transition".

I comment on the article entitled “Puzzle of protein dynamical transition” by Magazu et al. appearing in a recent issue of the Journal of Physical Chemistry B. The protein dynamical transition (PDT) is a well established feature of solventcoupled protein dynamics usually identified from a striking increase of apparent molecular displacements above a certain onset temperature, Ton ≈ 200−240 K. It is suggestive to invoke a scenario, originally proposed by Parak and Frauenfelder, of enhanced fluctuation amplitudes due to a detrapping transition, controlled by a multiple energy minima landscape: At a characteristic temperature Ton, the thermally activated protein changes its dynamic properties from rigid to flexible. This model predicts a fixed Ton, if the energy traps are deep and if the trapping rate is fast enough compared to the instrumental resolution. This model of the PDT was fully adopted by the elastic neutron scattering community and is now dismissed in ref 1 based on three statements: