Hsp70 gets destroyed (left) unless unfolded protein (cBSA; right) is around.


During heat shock recovery, a helper becomes a destroyer, say Shu-Bing Qian, Cam Patterson, and colleagues (University of North Carolina, Chapel Hill, NC).

The traitor protein is called CHIP. After the group discovered CHIP, their interest was piqued when they realized it was both an Hsp70-binding protein and a ubiquitin ligase. The finding suggested that “folding versus degradation is a regulated decision, not a stochastic decision, and CHIP ties together these two processes,” says Patterson.

They now find that CHIP helps to mark unfolded proteins that are bound to Hsp70 by adding the ubiquitin destruction signal. But once those marked proteins are destroyed, the Hsp70 itself becomes CHIP's next target. The effect could be reconstituted in vitro with only unfolded protein, Hsp70, and CHIP.

The resultant return to baseline Hsp70 levels is important to restore cellular normality. Hsp70 helps halt the cell cycle and alter signaling pathways so that cells can recover from stress. Once unfolded proteins are cleared, says Patterson, “the cell has to get out of this suspended animation phase.”


Qian, S.-B., et al.