Using Pseudocontact Shifts and Residual Dipolar Couplings as Exact NMR Restraints for the Determination of Protein Structural Ensembles

Nuclear magnetic resonance (NMR) spectroscopy provides detailed information about the structure and dynamics of proteins by exploiting the conformational dependence of the magnetic properties of certain atomic nuclei. The mapping between NMR measurements and molecular structures, however, often requires approximated descriptions based on the fitting of a number of parameters, thus reducing the quality of the information available from the experiments. To improve on this limitation, we show here that it is possible to use pseudocontact shifts and residual dipolar couplings as "exact" NMR restraints. We implement this strategy by using a replica-averaging method and illustrate its application by calculating an ensemble of structures representing the dynamics of the two-domain protein calmodulin.