Department of Ophthalmology, University of California, San Francisco, San Francisco, CA 94143, USA.
Center of Human and Molecular Biology and Center for Molecular Signaling, Department of Medical Biochemistry and Molecular Biology, Saarland University School of Medicine, Homburg, Germany.
Dev Cell. 2023 Apr 24;58(8):677-693.e9. doi: 10.1016/j.devcel.2023.03.003. Epub 2023 Apr 4.
Many G protein-coupled receptors (GPCRs) reside within cilia of mammalian cells and must undergo regulated exit from cilia for the appropriate transduction of signals such as hedgehog morphogens. Lysine 63-linked ubiquitin (UbK63) chains mark GPCRs for regulated removal from cilia, but the molecular basis of UbK63 recognition inside cilia remains elusive. Here, we show that the BBSome-the trafficking complex in charge of retrieving GPCRs from cilia-engages the ancestral endosomal sorting factor target of Myb1-like 2 (TOM1L2) to recognize UbK63 chains within cilia of human and mouse cells. TOM1L2 directly binds to UbK63 chains and the BBSome, and targeted disruption of the TOM1L2/BBSome interaction results in the accumulation of TOM1L2, ubiquitin, and the GPCRs SSTR3, Smoothened, and GPR161 inside cilia. Furthermore, the single-cell alga Chlamydomonas also requires its TOM1L2 ortholog in order to clear ubiquitinated proteins from cilia. We conclude that TOM1L2 broadly enables the retrieval of UbK63-tagged proteins by the ciliary trafficking machinery.
许多 G 蛋白偶联受体 (GPCR) 存在于哺乳动物细胞的纤毛内，为了适当传递信号（如 hedgehog 形态发生素），它们必须经历从纤毛的调节性退出。赖氨酸 63 连接的泛素 (UbK63) 链标记 GPCR 以进行调节性去除，但 UbK63 在纤毛内的识别的分子基础仍然难以捉摸。在这里，我们表明，负责从纤毛中回收 GPCR 的 BBSome-运输复合物-与古老的内体分选因子 Myb1 样 2 (TOM1L2) 的靶标结合，以识别人源和鼠源细胞纤毛内的 UbK63 链。TOM1L2 直接结合 UbK63 链和 BBSome，并且靶向破坏 TOM1L2/BBSome 相互作用会导致 TOM1L2、泛素和 GPCRs SSTR3、Smoothened 和 GPR161 在纤毛内积累。此外，单细胞藻类衣藻也需要其 TOM1L2 同源物才能从纤毛中清除泛素化蛋白。我们得出结论，TOM1L2 广泛地使纤毛运输机制能够回收 UbK63 标记的蛋白。
