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

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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.