Autosomal recessive spastic ataxia of Charlevoix-Saguenay is a fatal brain disorder featuring cerebellar neurodegeneration leading to spasticity and ataxia. This disease is caused by mutations in the SACS gene that encodes sacsin, a massive 4579-amino acid protein with multiple modular domains. However, molecular details of the function of sacsin are not clear. Here, using live cell imaging and biochemistry, we demonstrate that sacsin binds to microtubules and regulates microtubule dynamics. Loss of sacsin function in various cell types, including knockdown and KO primary neurons and patient fibroblasts, leads to alterations in lysosomal transport, positioning, function, and reformation following autophagy. Each of these phenotypic changes is consistent with altered microtubule dynamics. We further show the effects of sacsin are mediated at least in part through interactions with JIP3, an adapter for microtubule motors. These data reveal a new function for sacsin that explains its previously reported roles and phenotypes.

Charlevoix-Saguenay 的常染色体隐性痉挛性共济失调是一种致命的脑部疾病，其特征是小脑神经变性导致痉挛和共济失调。这种疾病是由SACS中的突变引起的编码 sacsin 的基因，sacsin 是一种具有多个模块结构域的大量 4579 个氨基酸的蛋白质。然而，sacsin 功能的分子细节尚不清楚。在这里，我们使用活细胞成像和生物化学证明 sacsin 与微管结合并调节微管动力学。各种细胞类型（包括敲低和 KO 原代神经元和患者成纤维细胞）中 sacsin 功能的丧失导致自噬后溶酶体转运、定位、功能和重组的改变。这些表型变化中的每一个都与改变的微管动力学一致。我们进一步表明，sacsin 的作用至少部分是通过与 JIP3（微管马达的适配器）的相互作用来介导的。这些数据揭示了 sacsin 的新功能，可以解释其先前报道的作用和表型。