Water and protein dynamics in sedimented systems: a relaxometric investigation

Sedimented proteins have recently been shown to provide solid-state NMR spectra of high quality, suitable for structural investigation. This is ascribed to the strong self-crowding effect, which apparently increases the reorientation time up to the point that the protein can be considered immobile on the NMR timescale. Herein, a relaxometric investigation of sedimented bovine serum albumin is performed to obtain information on the dynamics of the system. The measurement of the proton longitudinal relaxation rates as a function of the applied magnetic field indicates that the sedimented protein has relaxation properties very different from those of the protein in concentrated water solutions, even in the presence of glycerol, and similar to those of slightly rehydrated lyophilized systems. This study confirms the hypothesis that the reorientation of the protein molecules is largely abolished in sediments.