Probing protein structure by solvent perturbation of NMR spectra. Photochemically induced dynamic nuclear polarization and paramagnetic perturbation techniques applied to the study of the molten globule state of alpha-lactalbumin.

We have characterized the high-temperature molten globule state of bovine alpha-lactalbumin by a combined use of photochemically induced dynamic nuclear polarization and nitroxide surface perturbation. Both techniques are extremely well suited to follow the progressive increase of exposed surfaces in the native state and the appearance of partially or completely unfolded species. Our results suggest that the molten globule state obtained at high temperature and pH 7, and the state obtained at pH 2 are not only thermodynamically but also structurally very similar.