DNAJB6 mutants display toxic gain of function through unregulated interaction with Hsp70 chaperones

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Molecular chaperones, like DNAJB6, are crucial for protein folding and preventing aggregation.
• Mutations in DNAJB6 are linked to Limb-Girdle Muscular Dystrophy type 1D (LGMDD1), a dominant autosomal disorder.
• The precise molecular mechanisms underlying DNAJB6 mutation-induced dysfunction remain unclear.

Purpose of the Study:

• To investigate the structural and functional consequences of LGMDD1-associated DNAJB6 mutations.
• To elucidate the molecular mechanisms by which DNAJB6 mutations lead to myofibrillar degeneration.
• To explore potential therapeutic interventions targeting the DNAJB6-Hsp70 interaction.

Main Methods:

• Solution Nuclear Magnetic Resonance (NMR) spectroscopy to determine protein structure.
• Biochemical assays to assess protein function and chaperone activity.
• In vitro studies of wild-type (WT) and mutant DNAJB6 proteins.

Main Results:

• LGMDD1 mutants of DNAJB6 exhibit altered structures compared to WT DNAJB6.
• Disease mutants do not show reduced in vitro aggregation-prevention activity.
• Mutations disrupt the regulatory interaction between DNAJB6 and Hsp70 chaperones.
• Unregulated Hsp70 hyperactivation by mutants leads to Hsp70 depletion and proteostasis disruption.

Conclusions:

• LGMDD1 pathogenesis involves disrupted DNAJB6-Hsp70 chaperone regulation, not impaired aggregation prevention.
• Hyperactivation and depletion of Hsp70 contribute to the disease phenotype.
• Modulating DNAJB6-Hsp70 binding offers a potential therapeutic strategy for LGMDD1.