Instituto de Biología Funcional y Genómica (IBFG) and Departamento de Microbiología y Genética, CSIC-Universidad de Salamanca, Salamanca, Spain.
Instituto de Biología Molecular y Celular de Plantas, CSIC-Universitat Politècnica de València, Valencia, Spain.
FASEB J. 2021 Jun;35(6):e21615. doi: 10.1096/fj.202002610R.
Protein sorting at the trans-Golgi network (TGN) usually requires the assistance of cargo adaptors. However, it remains to be examined how the same complex can mediate both the export and retention of different proteins or how sorting complexes interact among themselves. In Saccharomyces cerevisiae, the exomer complex is involved in the polarized transport of some proteins from the TGN to the plasma membrane (PM). Intriguingly, exomer and its cargos also show a sort of functional relationship with TGN clathrin adaptors that is still unsolved. Here, using a wide range of techniques, including time-lapse and BIFC microscopy, we describe new molecular implications of the exomer complex in protein sorting and address its different layers of functional interaction with clathrin adaptor complexes. Exomer mutants show impaired amino acid uptake because it facilitates not only the polarized delivery of amino acid permeases to the PM but also participates in their endosomal traffic. We propose a model for exomer where it modulates the recruitment of TGN clathrin adaptors directly or indirectly through the Arf1 function. Moreover, we describe an in vivo competitive relationship between the exomer and AP-1 complexes for the model cargo Chs3. These results highlight a broad role for exomer in regulating protein sorting at the TGN that is complementary to its role as cargo adaptor and present a model to understand the complexity of TGN protein sorting.
蛋白质在跨高尔基网络 (TGN) 中的分拣通常需要货物衔接器的协助。然而，目前仍需研究同一复合物如何介导不同蛋白质的输出和保留，或者分拣复合物如何相互作用。在酿酒酵母中，外核体复合物参与了一些从 TGN 到质膜 (PM) 的极化运输的蛋白质。有趣的是，外核体及其货物与 TGN 网格蛋白衔接器之间也存在一种尚未解决的功能关系。在这里，我们使用包括延时和 BIFC 显微镜在内的一系列技术，描述了外核体复合物在蛋白质分拣中的新分子意义，并解决了其与网格蛋白衔接子复合物的不同功能相互作用层面。外核体突变体显示出氨基酸摄取受损，因为它不仅促进了氨基酸通透酶向 PM 的极化传递，而且还参与了它们的内体运输。我们提出了一个外核体模型，其中它通过 Arf1 功能直接或间接调节 TGN 网格蛋白衔接子的招募。此外，我们描述了外核体和 AP-1 复合物之间在模型货物 Chs3 上的体内竞争关系。这些结果突出了外核体在调节 TGN 蛋白质分拣中的广泛作用，这与其作为货物衔接子的作用相辅相成，并提出了一个模型来理解 TGN 蛋白质分拣的复杂性。
