Proper muscle development and function depend on myosin being properly folded and integrated into the thick filament structure. For this to occur the myosin chaperone UNC-45, or UNC-45B, must be present and able to chaperone myosin. Here we use a combination of in vivo C. elegans experiments and in vitro biophysical experiments to analyze the effects of six missense mutations in conserved regions of UNC-45/UNC-45B. We found that the phenotype of paralysis and disorganized thick filaments in 5/6 of the mutant nematode strains can likely be attributed to both reduced steady state UNC-45 protein levels and reduced chaperone activity. Interestingly, the biophysical assays performed on purified proteins show that all of the mutations result in reduced myosin chaperone activity but not overall protein stability. This suggests that these mutations only cause protein instability in the in vivo setting and that these conserved regions may be involved in UNC-45 protein stability/regulation via posttranslational modifications, protein–protein interactions, or some other unknown mechanism.

中文翻译：

---

肌球蛋白伴侣 UNC-45 保守残基的突变导致稳定性和伴侣活性降低

适当的肌肉发育和功能取决于肌球蛋白被正确折叠并整合到粗丝结构中。为此，肌球蛋白伴侣 UNC-45 或 UNC-45B 必须存在并且能够伴侣肌球蛋白。在这里，我们使用体内C. elegans的组合实验和体外生物物理实验分析了 UNC-45/UNC-45B 保守区域中六种错义突变的影响。我们发现，5/6 的突变线虫菌株中麻痹和杂乱的粗丝表型可能归因于稳态 UNC-45 蛋白水平降低和伴侣活性降低。有趣的是，对纯化蛋白质进行的生物物理测定表明，所有突变都会导致肌球蛋白伴侣活性降低，但不会导致整体蛋白质稳定性降低。这表明这些突变仅在体内环境中导致蛋白质不稳定，并且这些保守区域可能通过翻译后修饰、蛋白质-蛋白质相互作用或其他一些未知机制参与 UNC-45 蛋白质稳定性/调节。