The <scp>ALS</scp> ‐associated <scp>E425K</scp> mutation uncouples <scp>DNAJC7</scp> from the Hsp70 chaperone cycle

DNAJC7, a member of the J-domain protein (JDP/Hsp40) family, plays a key role in protein homeostasis by regulating Hsp70 activity and preventing protein aggregation. Mutations in DNAJC7 have been linked to amyotrophic lateral sclerosis (ALS); yet, the molecular mechanisms by which these variants impair chaperone function remain poorly understood. DNAJC7 is a conserved chaperone featuring both a canonical J-domain, essential for Hsp70 activation, and three TPR domains, which serve as protein-protein binding interfaces. Here, we investigate the structural and functional consequences of the ALS-associated E425K mutation located within the conserved J-domain. Using NMR spectroscopy, we show that although the E425K mutation does not alter the structure of the protein, it significantly disrupts the conserved J-domain-Hsp70 interaction. We further identify a second Hsp70-binding interface within the TPR domains, which interacts with the C-terminal EEVD motif of Hsp70. This TPR-EEVD interaction is preserved in the E425K mutant but cannot compensate for the loss of J-domain binding or restore DNAJC7-dependent Hsp70 activation. Functionally, we show that the TPR domains of DNAJC7 directly bind TDP-43 and prevent its aggregation and that this holdase activity is retained in the E425K mutant. However, the mutant fails to support client transfer to Hsp70 and the subsequent Hsp70-mediated substrate refolding. Together, these findings demonstrate that DNAJC7 requires coordinated action of both J-domain and TPRs to regulate Hsp70 function and that disruption of J-domain-mediated activation uncouples DNAJC7 from the Hsp70 cycle, providing a mechanistic basis for its dysfunction in ALS.