| In our work we investigated the chaperone function and quaternary structure formation of small heat-shock proteins. We have chosen two members of the small heat-shock family: alpha-crystallin, an abundant mammalian sHSP, and MjHSP16.5 from archebacteria Methanococcus jannaschii. With various physical and chemical methods (high pressure, change of the environmental pH) we modified the structure of these proteins, and investigated the related structural and functional changes.;The secondary structure changes of the examined proteins were small, or after the extreme acidic pH shock the secondary structure quickly regenerated. On the contrary, the quaternary structure changes were large, and after the perturbation there was no, or only very slow rearrangement of the quaternary structure.;We observed that after the preturbation, presumably the change in the quaternary structure caused an enhancement of the chaperon activity of the proteins. In case of alpha-crystallin we observed more quaternary structures belonging to the active state of the protein. The existence of more, active quaternary structures might be important in the adjustment of small heat-shock proteins to different stresses and substrates.;The high pressure experiments revealed a possible dissociation mechanism for MjHSP16.5, in which first water molecules enter the inner core of the protein. The experiments showed that the weak, secondary binding forces have an important role---beside the intermolecular beta-sheets---in maintaining the oligomeric structure of small heat-shock proteins. |
