A19: Functional and physical interaction between Hsp90 and Hsp70

Heat shock protein 90 (Hsp90) is an extremely abundant molecular chaperone. Hsp90 has roles in the folding and reactivation of hundreds of client proteins. Chaperones like Hsp90 complete their protein remodeling activities using energy generated from ATP hydrolysis. To complete the protein folding process, Hsp90 collaborates with many other co-chaperones, including the Hsp70 chaperone system. It has been observed previously that E. coli Hsp90 (Hsp90Ec) interacts and collaborates with E. coli Hsp70, DnaK. Molecular docking has indicated that this interaction occurs via an association between conserved regions on the middle domain of Hsp90Ec and on the nucleotide binding domain of DnaK. This direct physical interaction of the two chaperones has been confirmed through chemical crosslinking experiments. In this study, the E.coli Hsp90-Hsp70 docked model is used to study the modulation of Hsp90Ec by DnaK through a comparative normal mode analysis of the Hsp90Ec -DnaK complex and Hsp90 alone. In agreement with previous studies, we find that Hsp90Ec motions are represented by two dominant modes that correspond to a linear opening/closing motion and a torsional motion. When DnaK is bound to the Hsp90 dimer, only the motions of the Hsp90Ec protomer that is bound to DnaK are affected; the cooperativity of the motions between the Hsp90Ec domains of the bound protomer are increased relative to the unbound Hsp90Ec dimer. In the motions of the docked model, the largest displacements of DnaK occur in the substrate binding domain (SBD). The motions of the DnaK SBD are also observed to be correlated to the motions of the Hsp90Ec bound protomer and anticorrelated to the nucleotide binding domain of DnaK. These results are consistent with a substrate protein handoff between DnaK and Hsp90Ec. Currently, we are investigating the effects of stoichiometry of DnaK and Hsp90Ec. We have generated a complex with two DnaK molecules bound to the Hsp90Ec dimer and are further examining the normal modes of this complex.

Authors: Kate Connors

Faculty Advisor: Andrea N. Kravats, Department of Chemistry and Biochemistry

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