Conformational Dynamics of Substrate in the Active Site of Cytochrome P450 BM-3/NPG Complex: Insights from NMR Order Parameters

Ligand NMR order parameters are calculated from replica exchange molecular dynamics simulations of the cytochrome P450 BM-3/NPG complex. These are found to be in agreement with experimental NMR order parameters at room temperature consistent with an equilibrium between unproductive and productive conformations of this complex, with the latter state being predominant at physiological temperatures. The calculations show that the low experimental order parameters at room temperature reflect angular motion of the productive state rather than transitions from one state to the other. The wider distribution of bond orientations and concomitant lower-order parameters of the terminal bond of the ligand corresponding to the productive state is consistent with the proposal for an entropic mechanism for the stabilization of the productive conformational state. This study further supports the recently proposed thermal activation mechanism for this enzymatic system.