Vitale G, Rybin V, Christoforidis S, Thornqvist P, McCaffrey M, Stenmark H, Zerial M
European Molecular Biology Laboratory, Postfach 10.2209, D-69012 Heidelberg, Germany.
EMBO J. 1998 Apr 1;17(7):1941-51. doi: 10.1093/emboj/17.7.1941.
Rabaptin-5 functions as an effector for the small GTPase Rab5, a regulator of endocytosis and early endosome fusion. We have searched for structural determinants that confer functional specificity on Rabaptin-5. Here we report that native cytosolic Rabaptin-5 is present in a homodimeric state and dimerization depends upon the presence of its coiled-coil predicted sequences. A 73 residue C-terminal region of Rabaptin-5 is necessary and sufficient both for the interaction with Rab5 and for Rab5-dependent recruitment of the protein on early endosomes. Surprisingly, we uncovered the presence of an additional Rab-binding domain at the N-terminus of Rabaptin-5. This domain mediates the direct interaction with the GTP-bound form of Rab4, a small GTPase that has been implicated in recycling from early endosomes to the cell surface. Based on these results, we propose that Rabaptin-5 functions as a molecular linker between two sequentially acting GTPases to coordinate endocytic and recycling traffic.
Rabaptin-5作为小GTP酶Rab5的效应器发挥作用，Rab5是内吞作用和早期内体融合的调节因子。我们已经寻找了赋予Rabaptin-5功能特异性的结构决定因素。在此我们报告，天然胞质Rabaptin-5以同二聚体状态存在，二聚化取决于其卷曲螺旋预测序列的存在。Rabaptin-5的一个73个残基的C末端区域对于与Rab5的相互作用以及该蛋白在早期内体上的Rab5依赖性募集都是必需且充分的。令人惊讶的是，我们在Rabaptin-5的N末端发现了一个额外的Rab结合结构域。该结构域介导与Rab4的GTP结合形式的直接相互作用，Rab4是一种小GTP酶，与从早期内体到细胞表面的再循环有关。基于这些结果，我们提出Rabaptin-5作为两个顺序作用的GTP酶之间的分子连接物，以协调内吞和再循环运输。
