Nagelkerken B, Van Anken E, Van Raak M, Gerez L, Mohrmann K, Van Uden N, Holthuizen J, Pelkmans L, Van Der Sluijs P
Department of Cell Biology, Utrecht University School of Medicine, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands.
Biochem J. 2000 Mar 15;346 Pt 3(Pt 3):593-601.
The small GTPase rab4a is associated with early endocytic compartments and regulates receptor recycling from early endosomes. To understand how rab4a mediates its function, we searched for proteins which associate with this GTPase and regulate its activity in endocytic transport. Here we identified rabaptin4, a novel effector molecule of rab4a. Rabaptin4 is homologous with rabaptin5 and contains a C-terminal deletion with respect to rabaptin5. Rabaptin4 preferentially interacts with rab4a-GTP and to a lesser extent with rab5aGTP. We identified a rab4a-binding domain in the N-terminal region of rabaptin4, and two binding sites for rab5, including a novel N-terminal rab5a-binding site. Rabaptin4 is a cytosolic protein that inhibits the intrinsic GTP hydrolysis rate of rab4a and is recruited by rab4a-GTP to recycling endosomes enriched in cellubrevin and internalized indocarbocyanine-3 (Cy3)-labelled transferrin. We propose that rabaptin4 assists in the docking of transport vesicles en route from early endosomes to recycling endosomes.
小GTP酶rab4a与早期内吞小室相关，并调节受体从早期内体的循环利用。为了解rab4a如何介导其功能，我们寻找了与该GTP酶相关并在胞吞运输中调节其活性的蛋白质。在此，我们鉴定出rabaptin4，它是rab4a的一种新型效应分子。Rabaptin4与rabaptin5同源，相对于rabaptin5而言，它在C末端有缺失。Rabaptin4优先与rab4a-GTP相互作用，与rab5aGTP的相互作用程度较低。我们在rabaptin4的N末端区域鉴定出一个rab4a结合结构域，以及两个rab5结合位点，其中包括一个新的N末端rab5a结合位点。Rabaptin4是一种胞质蛋白，它能抑制rab4a的内在GTP水解速率，并被rab4a-GTP招募到富含细胞ubrevin和内化吲哚花青绿-3（Cy3）标记转铁蛋白的循环内体中。我们认为rabaptin4有助于运输小泡从早期内体到循环内体的对接。
