Division of Biochemistry and Molecular Biology, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.
Proc Natl Acad Sci U S A. 2010 Nov 9;107(45):19338-43. doi: 10.1073/pnas.1010554107. Epub 2010 Oct 25.
The activation and recruitment of the small GTPase Rab7 to early endosome is a critical step for early to late endosome maturation, a process that requires the class III phosphatidylinositol 3-kinase (PI3KC3) and GTPase regulators. However, the molecular mechanism underlying Rab7 activation and endosome maturation is still poorly defined. Here we report that Rubicon, a component of the PI3KC3 complex, prevents endosome maturation through differential interactions with Rab7 and UVRAG. UVRAG activates PI3KC3 and C-VPS/HOPS, a guanine nucleotide exchange factor that catalyzes the exchange of GDP for GTP on Rab7. We demonstrate that Rubicon sequesters UVRAG from C-VPS/HOPS. Active GTP-bound Rab7 competes for Rubicon binding and releases UVRAG to associate with C-VPS/HOPS, which in turn promotes further loading of Rab7 with GTP. This feed-forward loop ensures rapid amplification of GTP-bound Rab7 and consequent stimulation of endosome maturation. Hence, Rubicon serves as a previously unknown Rab7 effector to ensure the proper progression of the endocytic pathway.
小 GTP 酶 Rab7 向早期内体的激活和募集是早期到晚期内体成熟的关键步骤，这一过程需要 III 类磷酸肌醇 3-激酶 (PI3KC3) 和 GTPase 调节剂。然而，Rab7 激活和内体成熟的分子机制仍未完全确定。在这里，我们报告说 Rubicon 是 PI3KC3 复合物的一个组成部分，通过与 Rab7 和 UVRAG 的差异相互作用来阻止内体成熟。UVRAG 激活 PI3KC3 和 C-VPS/HOPS，后者是一种鸟嘌呤核苷酸交换因子，可催化 Rab7 上 GDP 与 GTP 的交换。我们证明 Rubicon 将 UVRAG 与 C-VPS/HOPS 隔离开来。活性 GTP 结合的 Rab7 竞争与 Rubicon 的结合，并释放 UVRAG 与 C-VPS/HOPS 结合，这反过来又促进了 Rab7 与 GTP 的进一步加载。这种正反馈环确保了 GTP 结合的 Rab7 的快速扩增，并随后刺激了内体成熟。因此，Rubicon 作为一种以前未知的 Rab7 效应物，可确保内吞途径的正常进行。
