The Hsp60 C-terminus Senses Substrate and Triggers Allosteric ATP Hydrolysis

Abstract

The human mitochondrial chaperonin Hsp60/Hsp10 plays an essential role in maintaining protein homeostasis through an ATP dependent protein refolding mechanism. In the absence of this chaperonin, all cells perish due to an accumulation of misfolded aggregates. Despite its importance, the detailed mechanism of ATP hydrolysis and the role of the C-terminal tail remains unresolved. Here we show that the C-terminal tail acts as a sensor for the arrival of substrate into the chaperonin internal chamber that directly leads to an allosteric trigger of ATP hydrolysis in a neighboring subunit. Our results reveal that removal of the C-terminal tail leads to normal binding of both ATP and a misfolded substrate, but the chaperonin stalls and is unable to progress along the protein folding reaction cycle because it has lost the ability to sense the presence of substrate. High resolution reconstructions reveal the detailed mechanism of ATP hydrolysis where access to the {gamma}-phosphate is blocked by the carboxylate oxygen of an aspartate residue. Binding of the C-terminal tail to substrate displaces this oxygen and allows ATP hydrolysis. These results bring a better understanding of how Hsp60 functions at an atomic level where substrate arrival activates ATP hydrolysis through an allosteric trigger.