Myopathy-causing mutations in an HSP40 chaperone disrupt processing of specific client conformers

Area of Science:

• Molecular biology
• Protein biochemistry
• Neuroscience

Background:

• The molecular chaperone network is crucial for preventing toxic protein misfolding and aggregation.
• Disruption of this network causes protein conformational disorders, including limb-girdle muscular dystrophy type 1D (LGMD1D).
• LGMD1D is linked to mutations in the DNAJB6 chaperone, specifically within its conserved G/F domain, whose function remains unclear.

Purpose of the Study:

• To investigate the role of the DNAJB6 G/F domain in chaperone function and LGMD1D pathogenesis.
• To understand how LGMD1D-associated mutations affect chaperone-mediated processing of aggregation-prone proteins.

Main Methods:

• Utilized a yeast HSP40 chaperone (Sis1) with known aggregation-prone clients to study DNAJB6 G/F domain function.
• Created a Sis1-DNAJB6 chimera to assess the impact of LGMD1D mutations on yeast prion processing ([RNQ+] and [PSI+]).
• Analyzed the effect of DNAJB6 G/F domain mutants on TDP-43 stress granule processing in mammalian cells.

Main Results:

• LGMD1D mutations in the Sis1-DNAJB6 chimera differentially impaired the processing of specific yeast prion conformers.
• These impairments did not directly correlate with prion strain sensitivity to chaperone levels.
• DNAJB6 G/F domain mutants disrupted the processing of nuclear TDP-43 stress granules in mammalian cells.

Conclusions:

• The DNAJB6 G/F domain mediates selective chaperone-substrate interactions, recognizing specific protein conformers.
• Disruption of this selective interaction by LGMD1D mutations can lead to the accumulation of toxic protein aggregates.
• This mechanism may underlie the development of LGMD1D and other protein conformational disorders.