Funtional analysis of Rhes, a novel Ras family protein, in neuronal cell

Rhes是Ras家族小gtp结合蛋白的一员。Rhes在大脑中，尤其是纹状体中大量表达，因此被称为Ras同源体。在本研究中，我们旨在鉴定Rhes的下游效应分子，从而深入了解Rhes的神经元功能。Rhes的效应结合域与典型Ras同源物不同，表明Rhes与非典型Ras效应物存在相互作用。Ras家族中只有一个成员Rap2与Rhes具有相似的效应结合区。Rap2与Rhes在效应结合结构域的第8位共享Phe残基，其中Ras具有Ser。Rap2在大脑中表达，并参与神经元功能。因此我们推断Rhes和Rap2可能具有共同的非典型Ras效应子。我们使用酵母双杂交筛选和亲和纯化-质谱法来寻找ries或rap2结合蛋白。出乎意料的是，我们分离到了不同的Rhes和Rap2结合蛋白，如ARMS（用于Rhes）和MAP4K4（用于Rap2）。ARMS是NGF受体的下游分子，而MAP4K4的果蝇同源物调节神经元轴突靶向。需要进一步的研究来阐明这些发现的生理意义。

Rhes is a member of the Ras family small GTP-binding proteins. Rhes is expressed abundantly in brain, especially in striatum, and thus designated Ras homologue enriched in striatum. In the present study, we aimed at identifying a downstream effector molecule of Rhes thereby gaining insights into Rhes's neuronal function. Rhes's effector-binding domain is different from those of typical Ras homologue, suggesting interaction of Rhes with non-typical Ras effectors. Only one member of Ras family, Rap2, shares similar effector-binding region with Rhes. Rap2 shares Phe residue at the 8th position of effector-binding domain with Rhes, where Ras has Ser. Rap2 is expressed in brain and implicated in neuronal functions as well. We therefore reasoned that Rhes and Rap2 could share common non-typical Ras effectors. We used the yeast two-hybrid screening and affinity purification-mass spectrometry approach to search for Rlies-or Rap2-binding proteins. Unexpectedly, we isolated different binding proteins for Rhes and Rap2, such as ARMS(for Rhes) and MAP4K4(for Rap2). ARMS is a downstream molecule of NGF receptor, while MAP4K4's Drosophila homologue regulates neuronal axon targeting. Further studies are necessary to clarify physiological significances of these findings.