S. Combet, J.-M. Zanotti, M.-C. Bellissent-Funel
We focus on temperature- and hydration-dependence of internal molecular motions in stripped human red blood cell (RBC) vesicles, widely used as a model system for more complex biomembranes.
We singled out picosecond local motions of the non-exchangeable hydrogen atoms of RBC vesicles by performing elastic and quasielastic incoherent neutron scattering measurements in dry and heavy water(D2O)-hydrated RBC powders.
In dry stripped RBCs, hydrogen motions remained harmonic all along the measured temperature range (100–310 K) and mean–square displacements (MSDs) exhibited no temperature transition up to 310 K. In contrast, MSDs of hydrated stripped RBCs (h≈0.38 g D2O/g dry powder) exhibited a pronounced transition near 260 K, with the sharp rise of anharmonic diffusive motions of hydrogen atoms. This transition at ~260 K was correlated with both the onset of nonvibrational (harmonic and nonharmonic) motions and the melting of crystallized hydration water.
In conclusion, we have shown that MSDs in human RBC vesicles are temperature-and hydration-dependent. These results provide insight into biomembrane internal dynamics at picosecond timescale and nanometer length scale. Such motions have been shown to act as the “lubricant” of larger conformational changes on a slower, millisecond timescale that are necessary for important biological processes.