BACKGROUND TPX2 (Targeting Protein for Xklp2) is essential for spindle assembly, activation of the mitotic kinase Aurora A and for triggering microtubule nucleation. Homologs of TPX2 in Chordata and plants were previously identified. Currently, proteins of the TPX2 family have little structural information and only small parts are covered by defined protein domains. METHODS We have used computational sequence analyses and structural predictions of proteins of the TPX2 family, supported with Circular Dichroism (CD) measurements. RESULTS Here, we report our finding that the C-terminal domain of TPX2, which is responsible of its microtubule nucleation capacity and is conserved in all members of the family, is actually formed by tandem repeats, covering well above 2/3 of the protein. We propose that this region forms a flexible solenoid involved in protein-protein interactions. Structural prediction and molecular modeling, combined with Circular Dichroism (CD) measurements reveal a predominant alpha-helical content. Furthermore, we identify full length homologs in fungi and shorter homologs with a different domain organization in diptera (including a paralogous expansion in Drosophila). CONCLUSIONS Our results, represent the first computational and biophysical analysis of the TPX2 proteins family and help understand the structure and evolution of this conserved protein family to direct future structural studies.

中文翻译：

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TPX2 的 C 末端结构域由 α 螺旋串联重复序列组成。


背景 TPX2（Xklp2 的靶向蛋白）对于纺锤体组装、有丝分裂激酶 Aurora A 的激活以及触发微管成核至关重要。先前已鉴定出脊索动物和植物中 TPX2 的同源物。目前，TPX2 家族的蛋白质几乎没有结构信息，并且只有一小部分被定义的蛋白质结构域覆盖。方法我们使用了 TPX2 家族蛋白质的计算序列分析和结构预测，并得到圆二色性 (CD) 测量的支持。结果在这里，我们报告了我们的发现，TPX2 的 C 末端结构域负责其微管成核能力，并且在该家族的所有成员中都是保守的，实际上是由串联重复形成的，覆盖了远高于 2/3 的蛋白质。我们认为该区域形成一个参与蛋白质-蛋白质相互作用的柔性螺线管。结构预测和分子建模结合圆二色性 (CD) 测量揭示了主要的 α 螺旋含量。此外，我们还鉴定了真菌中的全长同源物和双翅目中具有不同结构域组织的较短同源物（包括果蝇中的旁系同源扩展）。结论我们的结果代表了对 TPX2 蛋白家族的首次计算和生物物理分析，有助于了解这个保守蛋白家族的结构和进化，以指导未来的结构研究。