NMR Characterization of a “Fibril-Ready” State ofDemetalated Wild-Type Superoxide Dismutase

Demetallated superoxide dismutase (SOD1) is a transient species, fibrillogenic in nature, of great biomedical interest. It is a conformationally disordered protein difficult to characterize. We have developed a strategy based on the NMR investigation of a crystalline species characterized by X-ray crystallography and on the comparison of the solid state-solution state chemical shifts. The solid state assignment has been also helpful in assigning the solution spectra. The solution NMR spectra presumably detect species which are the result of equilibria among multiple species. From the differences in chemical shifts between the two forms we learned that a -sheet becomes conformationally labile and two loops in the same sheet show propensity to take a β conformation. This strategy, that exploits solution and solid state NMR spectra in a synergistic way, thus provides information on the species which are prone to oligomerization.