A R T I C L E S Substrate protein folds while it is bound to the ATP-independent chaperone Spy

Abstract

Chaperones are essential for maintaining protein-folding homeostasis, and they have important roles in the cellular stress response. By binding to aggregation-sensitive folding intermediates, chaperones inhibit aberrant interactions between proteins. The most intensively studied folding chaperones, such as the GroEL-GroES and DnaK systems, facilitate substrate protein folding through ATP-and cofactor-driven conformational changes In contrast to ATP-dependent chaperones, a number of chaperones have been identified that can assist in protein folding in the absence of ATP The mechanism by which Spy and the growing class of ATPindependent chaperones function to refold proteins in the absence of energy cofactors is an unresolved question. We addressed this by determining how Spy affects the folding pathway of Im7, the protein that was used to discover Spy. Im7 has a number of attributes that facilitate its study. It is small and monomeric, and it folds via a wellcharacterized mechanism that involves transition through a partially folded on-pathway intermediate before the native state is reache