Large Rotation of the N-terminal Domain of Hsp90 Is Important for Interaction with Some but Not All Client Proteins.

The 90-kDa heat shock protein (Hsp90) chaperones the late folding steps of many protein kinases, transcription factors, and a diverse set of other protein clients not related in sequence and structure. Hsp90's interaction with clients appears to be coupled to a series of conformational changes. How these conformational changes contribute to its chaperone activity is currently unclear. Using crosslinking, hydrogen exchange mass spectrometry, and fluorescence experiments, we demonstrate here that the N-terminal domain of Hsp90 rotates by approximately 180° as compared to the crystal structure of yeast Hsp90 in complex with Sba1 and AMPPNP. Surprisingly, Aha1 but not Sba1 suppresses this rotation in the presence of AMPPNP but not in its absence. A minimum length of the largely unstructured linker between N-terminal and middle domain is necessary for this rotation, and interfering with the rotation strongly affects the interaction with Aha1 and the intrinsic and Aha1-stimulated ATPase activity. Surprisingly, suppression of the rotation only affects the activity of some clients and does not compromise yeast viability.

Chaperome screening leads to identification of Grp94/Gp96 and FKBP4/52 as modulators of the α-synuclein-elicited immune response.

We have investigated the potential role of molecular chaperones as modulators of the immune response by using α-synuclein (αSyn) as an aggregation-prone model protein. We first performed an in vitro immunoscreening with 21 preselected candidate chaperones and selected 2 from this set as displaying immunological activity with differential profiles, Grp94/Gp96 and FKBP4/52. We then immunized mice with both chaperone/α-synuclein combinations using monomeric or oligomeric α-synuclein (MαSyn or OαSyn, respectively), and we characterized the immune response generated in each case. We found that Grp94 promoted αSyn-specific T-helper (Th)1/Th17 and IgG1 antibody responses (up to a 3-fold increase) with MαSyn and OαSyn, respectively, coupled to a Th2-type general phenotype (generating 2.5-fold higher IgG1/IgG2 levels). In addition, we observed that FKBP4 favored a Th1-skewed phenotype with MαSyn but strongly supported a Th2-type phenotype with OαSyn (with a 3-fold higher IL-10/IFN-γ serum levels). Importantly, results from adoptive transfer of splenocytes from immunized animals in a Parkinson's disease mouse model indicates that these effects are robust, stable in time, and physiologically relevant. Taken together, Grp94 and FKBP4 are able to generate differential immune responses to α-synuclein-based immunizations, depending both on the nature of the chaperone and on the aggregation state of α-synuclein. Our work reveals that several chaperones are potential modulators of the immune response and suggests that different chaperones could be exploited to redirect the amyloid-elicited immunity both for basic studies of the immunological processes associated with neurodegeneration and for immunotherapy of pathologies associated with protein misfolding and aggregation.

c-Abl Mediated Tyrosine Phosphorylation of Aha1 Activates Its Co-chaperone Function in Cancer Cells.

The ability of Heat Shock Protein 90 (Hsp90) to hydrolyze ATP is essential for its chaperone function. The co-chaperone Aha1 stimulates Hsp90 ATPase activity, tailoring the chaperone function to specific "client" proteins. The intracellular signaling mechanisms directly regulating Aha1 association with Hsp90 remain unknown. Here, we show that c-Abl kinase phosphorylates Y223 in human Aha1 (hAha1), promoting its interaction with Hsp90. This, consequently, results in an increased Hsp90 ATPase activity, enhances Hsp90 interaction with kinase clients, and compromises the chaperoning of non-kinase clients such as glucocorticoid receptor and CFTR. Suggesting a regulatory paradigm, we also find that Y223 phosphorylation leads to ubiquitination and degradation of hAha1 in the proteasome. Finally, pharmacologic inhibition of c-Abl prevents hAha1 interaction with Hsp90, thereby hypersensitizing cancer cells to Hsp90 inhibitors both in vitro and ex vivo.

Hsp90 inhibits α-synuclein aggregation by interacting with soluble oligomers.

Aggregated α-synuclein is one of the main components of the pathological Lewy bodies associated with Parkinson's disease (PD). Many other proteins, including chaperones such as Hsp90 and Hsp70, have been found co-localized with Lewy bodies and the expression levels of Hsp90 have been found to be increased in brains of PD patients. Although the role of Hsp70 in the aggregation of α-synuclein has been extensively studied, relatively little is known about the effect of Hsp90 on this process. Here, we have investigated if Hsp90 can prevent the aggregation of the A53T pathological mutant of α-synuclein in vitro. A detailed study using many biophysical methods has revealed that Hsp90 prevents α-synuclein from aggregating in an ATP-independent manner and that it forms a strong complex with the transiently populated toxic oligomeric α-synuclein species formed along the aggregation pathway. We have also shown that, upon forming a complex with Hsp90, the oligomers are rendered harmless and nontoxic to cells. Thus, we have clear evidence that Hsp90 is likely to play an important role on these processes in vivo.