Enhancement of Chaperone-Mediated Protein Folding Through Substrate Protein Interactions with the Groel C-Termini
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Many essential proteins require the assistance of molecular chaperones to achieve and maintain their native, folded conformations. The E. coli GroEL-ES chaperonin system is capable of aiding the folding of the cellular proteome through several distinct mechanisms, including the blocking of intermolecular aggregation, the confinement of substrate proteins inside the GroEL-ES cavity, and the forced unfolding of substrate proteins to reinitiate the folding process. This study describes the role of the C-terminal residues of the GroEL protein enhancing of the folding of substrate proteins. The 23 C-terminal residues of the GroEL monomer partially consist of four tandem repeats of a Gly-Gly-Met motif, leading to an intrinsically disordered conformation. Visualized using cryo-electron microscopy, these residues extend from the bottom of a GroEL cavity and interact with substrate proteins both before and during the folding process; removal of these residues leads to deficiencies in substrate protein encapsulation and folding. Interactions between the C-terminal tails of GroEL and the substrate protein lead to changes in both the conformation of the substrate protein and the binding position on the GroEL cavity surface before folding begins. These changes result in the substrate protein adopting a more unfolded state and migrating deeper into the cavity. These effects were observed with two distinct substrate proteins, the carbonfixing enzyme RuBisCO and the metalloprotease PepQ, which have unrelated, dissimilar structural folds. Changes in the subsequent intra-cavity folding relative to folding in the absence of the GroEL C-termini were also observed for both proteins, indicating altered utilization of folding pathways or intermediates. Significantly, these alterations of substrate protein conformation and folding, which lead to the enhancement of folding rate, are independent of any passive mechanism of preventing aggregation, as PepQ has no propensity for aggregation under the employed conditions. The results of this study show that GroEL can actively enhance the folding of proteins by altering the conformation of the substrate protein, thus changing the folding pathway and directing it towards the native-state.
Weaver, Jeremy Scott (2015). Enhancement of Chaperone-Mediated Protein Folding Through Substrate Protein Interactions with the Groel C-Termini. Doctoral dissertation, Texas A & M University. Available electronically from