Kawasaki Masato, Shiba Tomoo, Shiba Yoko, Yamaguchi Yoshiki, Matsugaki Naohiro, Igarashi Noriyuki, Suzuki Mamoru, Kato Ryuichi, Kato Koichi, Nakayama Kazuhisa, Wakatsuki Soichi
Structural Biology Research Center, Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan.
Genes Cells. 2005 Jul;10(7):639-54. doi: 10.1111/j.1365-2443.2005.00865.x.
GGA (Golgi-localizing, gamma-adaptin ear domain homology, ARF-binding) proteins, which constitute a family of clathrin coat adaptor proteins, have recently been shown to be involved in the ubiquitin-dependent sorting of receptors, through the interaction between the C-terminal three-helix-bundle of the GAT (GGA and Tom1) domain (C-GAT) and ubiquitin. We report here the crystal structure of human GGA3 C-GAT in complex with ubiquitin. A hydrophobic patch on C-GAT helices alpha1 and alpha2 forms a binding site for the hydrophobic Ile44 surface of ubiquitin. Two distinct orientations of ubiquitin Arg42 determine the shape and the charge distribution of ubiquitin Ile44 surface, leading to two different binding modes. Biochemical and NMR data strongly suggest another hydrophobic binding site on C-GAT helices alpha2 and alpha3, opposite to the first binding site, also binds ubiquitin although weakly. The double-sided ubiquitin binding provides the GAT domain with higher efficiency in recognizing ubiquitinated receptors for lysosomal receptor degradation.
GGA（高尔基体定位、γ-衔接蛋白耳结构域同源物、ARF结合）蛋白构成了网格蛋白包被衔接蛋白家族，最近研究表明，通过GAT（GGA和Tom1）结构域的C端三螺旋束（C-GAT）与泛素之间的相互作用，该蛋白参与了受体的泛素依赖性分选。我们在此报告人GGA3 C-GAT与泛素复合物的晶体结构。C-GAT的α1和α2螺旋上的一个疏水区域形成了泛素疏水Ile44表面的结合位点。泛素Arg42的两种不同取向决定了泛素Ile44表面的形状和电荷分布，从而导致两种不同的结合模式。生化和核磁共振数据有力地表明，C-GAT的α2和α3螺旋上与第一个结合位点相对的另一个疏水结合位点也能结合泛素，尽管结合较弱。双面泛素结合使GAT结构域在识别用于溶酶体受体降解的泛素化受体时具有更高的效率。
