GroEL under heat-shock - Switching from a folding to a storing function

Chaperonin GroEL from Escherichia coli, together with its cochaperonin GroE S, are proteins involved in assisting the folding of polypeptides. GroEL is a tetradecamer composed of two heptameric rings, which enclose a cavity wh ere folding takes place through multiple cycles of substrate and GroES bind ing and release. GroEL and GroES are also heat-shock proteins, their synthe sis being increased during heat-shock conditions to help the cell coping wi th the thermal stress. Our results suggest that, as the temperature increas es, GroEL decreases its protein folding activity and starts acting as a "pr otein store." The molecular basis of this behavior is the loss of inter-rin g signaling, which slows down GroES liberation from GroEL and therefore the release of the unfolded protein from the GroEL cavity, This behavior is re versible, and after heat-shock, GroEL reverts to its normal function. This might have a physiological meaning, since under thermal stress conditions, it may be inefficient for the cell to fold thermounstable proteins that are prone to denaturation.