We examine whether the rate-promoting vibration of lactate dehydrogenase is a preferred axis of thermal energy transfer. While it seems plausible that such a mechanistically important motion is also a favored direction of energy transfer, none of the previous studies of rate-promoting vibrations in enzymatic catalysis have addressed this question. It is equally likely that the promoting vibration, though catalytically important, has no different properties than any other axis in the protein. Resolution of this issue is important for two reasons: First, if energy is transferred along this axis in a preferred fashion, it shows that the protein is engineered in a way that transfers thermal energy into a motion that is coupled to the chemical step. Second, the discovery of a preferred direction of thermal transfer provides a potential route to experimental verification of the promoting vibration concept. Our computational experiments are specifically designed to mimic potential laser experiment with the deposition of thermal energy in an active-site chromophore with subsequent measurement of temperature at various points in the protein. Our results indicate that the promoting vibration is indeed a preferred channel of energy transfer. In addition, we study the vibrational structure of the protein via the dynamical structure factor to show preferred vibrational motion along the promoting vibration axis is an inherent property of the protein structure via thermal fluctuations.
© 2011 American Chemical Society