Kukimoto-Niino Mutsuko, Sakamoto Ayako, Kanno Eiko, Hanawa-Suetsugu Kyoko, Terada Takaho, Shirouzu Mikako, Fukuda Mitsunori, Yokoyama Shigeyuki
Systems and Structural Biology Center, Yokohama Institute, RIKEN, 1-7-22 Suehiro-cho, Tsurumi, Yokohama 230-0045, Japan.
Structure. 2008 Oct 8;16(10):1478-90. doi: 10.1016/j.str.2008.07.014.
Rab27A is required for actin-based melanosome transport in mammalian skin melanocytes through its interaction with a specific effector, Slac2-a/melanophilin. Mutations that disrupt the Rab27A/Slac2-a interaction cause human Griscelli syndrome. The other Rab27 isoform, Rab27B, also binds all of the known effectors of Rab27A. In this study, we determined the crystal structure of the constitutively active form of Rab27B complexed with GTP and the effector domain of Slac2-a. The Rab27B/Slac2-a complex exhibits several intermolecular hydrogen bonds that were not observed in the previously reported Rab3A/rabphilin complex. A Rab27A mutation that disrupts one of the specific hydrogen bonds with Slac2-a resulted in the dramatic reduction of Slac2-a binding activity. Furthermore, we generated a Rab3A mutant that acquires Slac2-a binding ability by transplanting four Rab27-specific residues into Rab3A. These findings provide the structural basis for the exclusive association of Slac2-a with the Rab27 subfamily, whereas rabphilin binds several subfamilies, including Rab3 and Rab27.
Rab27A通过与特定效应器Slac2-a/黑色素亲和素相互作用，参与哺乳动物皮肤黑素细胞中基于肌动蛋白的黑素小体转运。破坏Rab27A/Slac2-a相互作用的突变会导致人类格里塞利综合征。另一种Rab27亚型Rab27B也能结合Rab27A所有已知的效应器。在本研究中，我们确定了与GTP和Slac2-a效应器结构域复合的组成型活性形式Rab27B的晶体结构。Rab27B/Slac2-a复合物表现出一些在先前报道的Rab3A/rabphilin复合物中未观察到的分子间氢键。破坏与Slac2-a的一个特定氢键的Rab27A突变导致Slac2-a结合活性显著降低。此外，我们通过将四个Rab27特异性残基移植到Rab3A中，生成了一种具有Slac2-a结合能力的Rab3A突变体。这些发现为Slac2-a与Rab27亚家族的排他性结合提供了结构基础，而rabphilin则结合包括Rab3和Rab27在内的几个亚家族。
