The Endosomal Sorting Complex Required for Transport machinery consists of four protein complexes (ESCRT 0‐IV) and the post ESCRT ATPase Vps4. ESCRT mediates cargo delivery for lysosomal degradation via formation of multivesicular bodies. Trypanosoma brucei contains orthologues of ESCRT I‐III and Vps4. Trypanosomes also have an ubiquitinylated invariant surface glycoprotein (ISG65) that is delivered to the lysosome by ESCRT, however, we previously implicated TbVps4 in rescue and recycling of ISG65. Here we use conditional silencing to investigate the role of TbVps24, a phosphoinositide‐binding ESCRT III component, on protein trafficking. TbVps24 localises to the TbRab7⁺ late endosome, and binds PI(3,5)P₂, the product of the TbFab1 kinase, both of which also localise to late endosomes. TbVps24 silencing is lethal, and negatively affects biosynthetic trafficking of the lysosomal markers p67 and TbCathepsin L. However, the major phenotype of silencing is accelerated degradation and depletion of the surface pool of ISG65. Thus, TbVps24 silencing phenocopies that of TbVps4 in regard to ISG65 trafficking. This presents a paradox since we have previously found that depletion of TbFab1 completely blocks ISG65 turnover. We propose a model in which late ESCRT components operate at two sites, one PI(3,5)P₂‐dependent (degradation) and one PI(3,5)P₂‐independent (recycling), to regulate ISG65 homeostasis.

中文翻译：

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晚期 ESCRT 机制介导了布氏锥虫中不变表面糖蛋白 65 的回收和拯救。

所述ë ndosomal小号奥廷Ç omplex ř equired为Ť ransport机械包括四个蛋白质复合物（ESCRT 0-IV）和后ESCRT ATP酶Vps4。ESCRT 通过形成多泡体来介导溶酶体降解的货物输送。布氏锥虫含有 ESCRT I-III 和 Vps4 的直向同源物。锥虫还具有通过 ESCRT 传递到溶酶体的泛素化不变表面糖蛋白 (ISG65)，然而，我们之前曾将 TbVps4 与 ISG65 的拯救和回收有关。在这里，我们使用条件沉默来研究 TbVps24（一种结合磷酸肌醇的 ESCRT III 成分）对蛋白质运输的作用。TbVps24 本地化到 TbRab7 ⁺晚期内体，并结合 PI(3,5)P ₂，这是 TbFab1 激酶的产物，两者也定位于晚期内体。TbVps24 沉默是致命的，并对溶酶体标记 p67 和 TbCathepsin L 的生物合成运输产生负面影响。 然而，沉默的主要表型是 ISG65 表面池的加速降解和消耗。因此，在 ISG65 贩运方面，TbVps24 沉默表型复制了 TbVps4 的表型。这提出了一个悖论，因为我们之前发现 TbFab1 的消耗完全阻止了 ISG65 周转。我们提出了一种模型，其中晚期 ESCRT 组件在两个位点运行，一个是 PI(3,5)P ₂依赖性（降解），一个是 PI(3,5)P ₂独立（回收），以调节 ISG65 稳态。