Murayama Kazutaka, Kato-Murayama Miyuki, Akasaka Ryogo, Terada Takaho, Yokoyama Shigeyuki, Shirouzu Mikako
Graduate School of Biomedical Engineering, Tohoku University, 2-1 Seiryo, Aoba, Sendai 980-8575, Japan.
Acta Crystallogr Sect F Struct Biol Cryst Commun. 2012 Dec 1;68(Pt 12):1455-9. doi: 10.1107/S1744309112045265. Epub 2012 Nov 19.
Xpln is a guanine nucleotide-exchange factor (GEF) for Rho GTPases. A Dbl homology (DH) domain followed by a pleckstrin homology (PH) domain is a widely adopted GEF-domain architecture. The Xpln structure solely comprises these two domains. Xpln activates RhoA and RhoB, but not RhoC, although their GTPase sequences are highly conserved. The molecular mechanism of the selectivity of Xpln for Rho GTPases is still unclear. In this study, the crystal structure of the tandemly arranged DH-PH domains of mouse Xpln, with a single molecule in the asymmetric unit, was determined at 1.79 Å resolution by the multiwavelength anomalous dispersion method. The DH-PH domains of Xpln share high structural similarity with those from neuroepithelial cell-transforming gene 1 protein, PDZ-RhoGEF, leukaemia-associated RhoGEF and intersectins 1 and 2. The crystal structure indicated that the α4-α5 loop in the DH domain is flexible and that the DH and PH domains interact with each other intramolecularly, thus suggesting that PH-domain rearrangement occurs upon RhoA binding.
Xpln是一种针对Rho GTP酶的鸟嘌呤核苷酸交换因子（GEF）。一个由Dbl同源结构域（DH）和其后的普列克底物蛋白同源结构域（PH）组成的结构是一种广泛采用的GEF结构域架构。Xpln的结构仅由这两个结构域组成。Xpln可激活RhoA和RhoB，但不能激活RhoC，尽管它们的GTP酶序列高度保守。Xpln对Rho GTP酶选择性的分子机制仍不清楚。在本研究中，采用多波长反常散射法，以1.79 Å的分辨率测定了小鼠Xpln串联排列的DH-PH结构域的晶体结构，不对称单元中有一个单分子。Xpln的DH-PH结构域与神经上皮细胞转化基因1蛋白、PDZ-RhoGEF、白血病相关RhoGEF以及intersectins 1和2的DH-PH结构域具有高度的结构相似性。晶体结构表明，DH结构域中的α4-α5环是灵活的，并且DH和PH结构域在分子内相互作用，因此表明在RhoA结合时会发生PH结构域重排。
