Uncovering the Role of DNAJB6 Chaperone Mutations in Myopathies

Molecular chaperones are essential cellular components which aid in protein folding and preventing the abnormal aggregation of disease-associated proteins. One such chaperone, DNAJB6, is a potent suppressor of aggregate and amyloid formation within cells.

Mutations in DNAJB6 chaperone were identified in patients with LGMD1D, an autosomal disorder characterized by accumulations of aggregated protein within muscle cells. The molecular mechanisms through which such mutations cause this dysfunction, however, are not well understood.

Interestingly, the majority of LGMD1D-related mutations are localized to the GF-rich linker region of DNAJB6, a domain with no previously identified function. We, however, have recently uncovered that in the DNAJB6 paralog, DNAJB1, the GF-rich region serves a regulatory role - preventing unregulated activation of the Hsp70 chaperone. This regulation is mediated by a helical structure in the N-terminal part of the GF-rich domain. Excitingly, such a helix is also present in DNAJB6, as evident from the recent DNAJB6 NMR structure.

Here we employed NMR to investigate the structural changes in the LGMD1D mutants of DNAJB6, and monitored their aggregation-suppression activities. We found that, surprisingly, the disease mutants, that show clear aggregate pathology in cells, did not reduce the chaperone activity of DNAJB6 and were all able to suppress amyloid formation in vitro. Rather, each of the six disease mutations caused structural changes to the GF-region affecting the helical structure. Furthermore, all the mutants interacted with Hsp70s in an unregulated manner, hyperactivating the chaperone. We believe these findings greatly advance our understanding of the contribution of DNAJB6 mutations to LGMD1D.