Crystal Structure of the Stress-Inducible Human Heat Shock Protein 70 Substrate-Binding Domain in Complex with Peptide Substrate

AbstractDnaJ/Hsp40 chaperones deliver unfolded proteins and stimulate the ATPase activity of DnaK/Hsp70 via their J-domain, a crucial event for the function that this system has in assisting protein folding. The interaction between Hsp40 and Hsp70 is transient and thus difficult to study, since mixing the binding partners can lead to quick dissociation due to their low affinity, creating a challenge for detailed analysis. As a consequence, knowledge of many important aspects of the mechanism of interaction is still lacking, for instance, the effect that J-domain binding has on Hsp70. In this study, we investigated whether it would be possible to gain understanding of this interaction by engineering a chimeric polypeptide where the J-domain of Hsp40 was covalently attached to the substrate binding domain (SBD) of Hsp70 by a flexible linker. The rationale for this is that an increase in the proximity between the interacting partners in this engineered chimera will promote the natural interaction and facilitate the characterization of the protein– protein interaction, which is a requirement to gain further understanding of many biological processes. The resulting chimera, termed J-SBD, was properly folded and had properties not present in the SBD alone. J-SBD behaved primarily as a monomer in all conditions tested and exhibited chaperone activity, as shown by aggregation protection and substrate binding assays, which revealed decreased binding to bis-ANS, a probe for hydrophobic patches. Collectively, our results suggest that Hsp40 binding to Hsp70 via the J-domain shifts the Hsp70 equilibrium towards the monomer state to expose hydrophobic sites prone to substrate accommodation.AbbreviationsBis-ANS (4,4’-Dianilino-1,1’-Binaphthyl-5,5’-Disulfonic Acid; CD, circular dichroism; Hsp, heat shock protein; J-SBD, chimeric polypeptide in which the J-domain of Hsp40 (at the N-terminus) is covalently attached to the substrate binding domain of Hsp70 (at the C-terminus) by a flexible linker; SBD: substrate binding domain of Hsp70.

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Necroptosis-blocking compound NBC1 targets heat shock protein 70 to inhibit MLKL polymerization and necroptosis

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1916503117 ◽

2020 ◽

Vol 117 (12) ◽

pp. 6521-6530 ◽

Cited By ~ 4

Author(s):

Andrea N. Johnston ◽

Yuyong Ma ◽

Hua Liu ◽

Shuzhen Liu ◽

Sarah Hanna-Addams ◽

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Keyword(s):

Heat Shock ◽

Heat Shock Protein ◽

Substrate Binding ◽

Kinase Domain ◽

Binding Domain ◽

Compound Libraries ◽

Cell Death Pathway ◽

Molecule Inhibitor ◽

Substrate Binding Domain

Necroptosis is a regulated necrotic cell death pathway involved in development and disease. Its signaling cascade results in the formation of disulfide bond-dependent amyloid-like polymers of mixed lineage kinase domain-like protein (MLKL), which mediate proinflammatory cell membrane disruption. We screened compound libraries provided by the National Cancer Institute and identified a small-molecule inhibitor of necroptosis named necroptosis-blocking compound 1 (NBC1). Biotin-labeled NBC1 specifically conjugates to heat shock protein Hsp70. NBC1 and PES-Cl, a known Hsp70 substrate-binding inhibitor, block the formation of MLKL polymers, but not MLKL tetramers in necroptosis-induced cells. In vitro,recombinant Hsp70 interacts with the N-terminal domain (NTD) of MLKL and promotes NTD polymerization, which has been shown to mediate the cell killing activity. Furthermore, the substrate-binding domain (SBD) of Hsp70 is sufficient to promote MLKL polymerization. NBC1 covalently conjugates cysteine 574 and cysteine 603 of the SBD to block its function. In addition, an SBD mutant with both cysteines mutated to serines loses its ability to promote MLKL polymerization. Interestingly, knockdown of Hsp70 in cells leads to MLKL destabilization, suggesting that MLKL might also be a client protein of Hsp70. In summary, using NBC1, an inhibitor of necroptosis, we identified Hsp70 as a molecular chaperone performing dual functions in necroptosis. It stabilizes MLKL protein under normal condition and promotes MLKL polymerization through its substrate-binding domain during necroptosis.

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