Propagation of experimental uncertainties using the Lipari-Szabo model-free analysis of protein dynamics

In this paper we make use of the graphical procedure previously described [ Jin, D. et al. (1997) J. Am. Chem. Sec., 119, 6923-6924] to analyze NMR rel axation data using the Lipari-Szabo model-free formalism. The graphical app roach is advantageous in that it allows the direct visualization of the exp erimental uncertainties in the motional parameter space. Some general 'rule s' describing the relationship between the precision of the relaxation meas urements and the precision of the model-free parameters and how this relati onship changes with the overall tumbling time (tau(m)) are summarized. The effect of the precision in the relaxation measurements on the detection of internal motions not close to the extreme narrowing limit is analyzed. We a lso show that multiple timescale internal motions may be obscured by experi mental uncertainty, and that the collection of relaxation data at very high field strength can improve the ability to detect such deviations from the simple Lipari-Szabo model.