Mesodynamics in the SARS nucleocapsid measured by NMR field cycling

Clarkson, Michael W.; Lei, Ming; Eisenmesser, Elan Z.; Labeikovsky, Wladimir; Redfield, Alfred; Kern, Dorothee

Model selection was performed using the Bayesian information criterion (BIC) with model elimination (d'Auvergne and Gooley 2003) and a modified jackknife approach in which 1-3 relaxation rates or NOEs were eliminated in each attempted fit. Residues for which more than one violation of model-free constraints (order parameters greater than one or less than zero, or s e /s s C s m ) occurred during the jackknife procedure were shifted to a simpler model. No residues experienced multiple violations during the jackknife when model 2 was used. The initial rounds of model selection included models that incorporate R EX corrections to the R 2 data (models 3 and 4). However, these models were not ultimately selected for any residues because CPMG relaxation dispersion gave no indication of R EX (data not shown), and refinement of model selection excluded those models. Accordingly, the only models used in the final analysis were model 2 (S 2 , s e ) (Lipari and Szabo 1982) , and model 5 (S 2 s , S 2 f , s s ) (Clore et al. 1990 ). The final model-free fits excluded the low-field data in the interest of accuracy (see below), but including these data did not generally change the fitted order parameter by more than 5%.