Molecular chaperones are essential cellular components that aid in protein folding and preventing the abnormal aggregation of disease-associated proteins. Mutations in one such chaperone, DNAJB6, were identified in patients with LGMDD1, a dominant autosomal disorder characterized by myofibrillar degeneration and accumulations of aggregated protein within myocytes. The molecular mechanisms through which such mutations cause this dysfunction, however, are not well understood. Here we employ a combination of solution NMR and biochemical assays to investigate the structural and functional changes in LGMDD1 mutants of DNAJB6. Surprisingly, we find that DNAJB6 disease mutants show no reduction in their aggregation-prevention activity in vitro, and instead differ structurally from the WT protein, affecting their interaction with Hsp70 chaperones. While WT DNAJB6 contains a helical element regulating its ability to bind and activate Hsp70, in LGMDD1 disease mutants this regulation is disrupted. These variants can thus recruit and hyperactivate Hsp70 chaperones in an unregulated manner, depleting Hsp70 levels in myocytes, and resulting in the disruption of proteostasis. Interfering with DNAJB6-Hsp70 binding, however, reverses the disease phenotype, suggesting future therapeutic avenues for LGMDD1.

分子伴侣是重要的细胞成分，有助于蛋白质折叠和防止疾病相关蛋白的异常聚集。在 LGMDD1 患者中发现了一种这样的伴侣 DNAJB6 的突变，LGMDD1 是一种显性常染色体疾病，其特征是肌原纤维变性和肌细胞内聚集蛋白的积累。然而，这种突变导致这种功能障碍的分子机制尚不清楚。在这里，我们采用溶液 NMR 和生化测定的组合来研究 DNAJB6 的 LGMDD1 突变体的结构和功能变化。令人惊讶的是，我们发现 DNAJB6 疾病突变体在体外的聚集预防活性没有降低，而是在结构上与 WT 蛋白不同，影响了它们与 Hsp70 伴侣的相互作用。虽然 WT DNAJB6 包含一个螺旋元件，可调节其结合和激活 Hsp70 的能力，但在 LGMDD1 疾病突变体中，这种调节被破坏。因此，这些变体可以不受调节的方式募集和过度激活 Hsp70 伴侣，消耗心肌细胞中的 Hsp70 水平，并导致蛋白质稳态中断。然而，干扰 DNAJB6-Hsp70 结合会逆转疾病表型，提示 LGMDD1 的未来治疗途径。