High Pressure Enhances the Chaperone Activity of the Oligomeric Protein Alpha-Crystallin

摘要

α-Crystallin, the major protein of vertebrate eye lens belongs to the small heat shock protein family. Presumably, its chaperone function plays an important role in the prevention of human cataract Several papers demonstrated, that its chaperone activity can be enhanced by temperature increase. We have shown that structural perturbation by high hydrostatic pressure in the range of 100 - 350 MPa also enhances this activity However, in contrast to the temperature-induced changes, the pressure-inducedenhancement is reversible. After pressure release the increased activity is lost on the time scale of hours. In this work, infrared and fluorescence spectroscopy and light scattering measurements were used to investigate the structural basis of the higher activity. Our results show that mainly the quaternary structure is influenced by pressure. Under pressure the interactions between the α crystallin subunits weaken, the oligomer size decreases, the environment of tryptophans becomes more polar and thehydrophobic surface exposed to solvent increases. The relaxation of the pressure effect involves processes on rather different time scales from minutes to tens of hours. The intermolecular interactions between subunits regain their strength within minutes, while the oligomer size is regained slowly with a characteristic time of several tens of hours. These data compared to the relaxation time of chaperone activity show, that both the oligomer size and the organization of subunits have their role in the chaperone function.