NMR studies of partially folded molten-globule states.
Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for the study of the structure, dynamics, and folding of proteins in solution. It is particularly powerful when applied to dynamic or flexible systems, such as partially folded molten-globule states of proteins, which are not usually amenable to X-ray crystallography. This chapter describes NMR methods suitable for the characterization of molten-globule states. These include pulsed-field-gradient NMR techniques for the measurement of the hydrodynamic radius, bulk and site-specific hydrogen-deuterium exchange experiments for the identification of regions of secondary structure, and 15N-edited NMR experiments carried out in increasing concentrations of denaturants, which allow the stability of different regions of the molten globule to be probed. Examples of the application of these methods to the study of the low-pH molten globule of human alpha-lactalbumin are presented.