Abstract
The infinitely short lifetime of transition states makes characterization extremely difficult. We have used a combination of molecular dynamics and experimental approaches to determine two important rate-limiting interactions involved in the allosteric transition of a signaling protein. Targeted MD simulations of the receiver domain of NtrC (Nitrogen Regulatory Protein C) were used to predict interactions that are important in stabilizing the transition state between the known inactive and active structures of the protein. Mutations were made to test these predictions and the rate of exchange between the two substates were measured by 15N-CPMG relaxation dispersion experiments. The results verify the importance of these key interactions in the transition pathway of NtrC. This work shows that targeted molecular dynamics together with experimental validation can be an invaluable tool at elucidating the structure and rate-limiting interactions of conformational transitions.