Functional synergy between Rab5 effector Rabaptin-5 and exchange factor Rabex-5 when physically associated in a complex
Functional synergy between Rab5 effector Rabaptin-5 and exchange factor Rabex-5 when physically associated in a complex
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DOI：
10.1091/mbc.12.7.2219
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发表时间：
2001-07-01
影响因子：
3.3
通讯作者：
Zerial, M
中科院分区：
文献类型：
--
作者：
Lippé, R;Miaczynska, M;Zerial, M
Rab GTP酶是囊泡运输机制的中心元件。一种新的观点认为，这些GTP酶的下游效应物是多蛋白复合体，包括核苷酸交换因子，以确保GTP酶激活和效应器功能之间的偶联。我们先前已经证明，Rab5调节早期内吞途径的各个运输步骤，由Rabex-5、Rab5核苷酸交换因子和效应器Rabaptin-5组成的复合体激活。我们推测，这两种蛋白的物理结合对于它们在依赖Rab5的内细胞膜运输中的活性是必要的。为了评估这种复合体形成的功能含义，我们使用重组蛋白对其进行了重组，并对其性质进行了表征。首先，我们发现Rabaptin-5增加了Rabex-5在Rab5上的交换活性。第二，Rabaptin-5依赖Rab5的募集到早期内吞体内完全依赖于它与Rabex-5的物理联系。第三，Rabaptin-5和Rabex-5之间的复合体形成是早期内体同型融合所必需的。这些结果揭示了Rabaptin-5和Rabex-5在该复合体中的功能协同作用，并对Rab和Rho GTP酶的类似复合体的功能具有一定的意义。
Rab GTPases are central elements of the vesicular transport machinery. An emerging view is that downstream effectors of these GTPases are multiprotein complexes that include nucleotide exchange factors to ensure coupling between GTPase activation and effector function. We have previously shown that Rab5, which regulates various steps of transport along the early endocytic pathway, is activated by a complex consisting of Rabex-5, a Rab5 nucleotide exchange factor, and the effector Rabaptin-5. We postulated that the physical association of these two proteins is necessary for their activity in Rab5-dependent endocytic membrane transport. To evaluate the functional implications of such complex formation, we have reconstituted it with the use of recombinant proteins and characterized its properties. First, we show that Rabaptin-5 increases the exchange activity of Rabex-5 on Rab5. Second, Rab5-dependent recruitment of Rabaptin-5 to early endosomes is completely dependent on its physical association with Rabex-5. Third, complex formation between Rabaptin-5 and Rabex-5 is essential for early endosome homotypic fusion. These results reveal a functional synergy between Rabaptin-5 and Rabex-5 in the complex and have implications for the function of analogous complexes for Rab and Rho GTPases.