Cross Validation of the Structure of a Transiently Formed and Low Populated FF Domain Folding Intermediate Determined by Relaxation Dispersion NMR and CS-Rosetta

The atomic resolution structure of a low populated and transiently formed on-pathway folding intermediate of the FF domain from human HYPA/FBP11 has recently been reported[1]. The structure was determined on the basis of backbone chemical shift and bond vector orientation restraints measured on the ‘invisible’ intermediate state using relaxation dispersion nuclear magnetic resonance (NMR) spectroscopy that were subsequently input into the data-base structure determination program CS-Rosetta. This thesis focuses on the cross-validation of the structure so produced. We present here the solution NMR structure of a mimic of the folding intermediate that is highly populated in solution, obtained from the wild-type domain by protein mutagenesis. The ensemble of structures generated of the mimic are within 2Å of the relaxation dispersion/CS-Rosetta structures of the intermediate, with the non-native interactions in the intermediate also observed in the mimic. The results presented in this thesis strongly confirm the structure of the FF domain folding intermediate, in particular, and validate the use of relaxation dispersion derived restraints in structural studies of invisible excited states, in general.MAS