一个新的阴道毛滴虫Ras同源cDNA克隆的分离及其特征分析(英文)

ISOLATION AND CHARACTERIZATION OF A NOVEL RAS HOMOLOGUE cDNA IN TRICHOMONAS VAGINALIS

Ras超家族是由一群具有保守氨基酸基序的GTP结合蛋白组成,作为双向分子开关对细胞的多种功能具有调节重要的作用。本文报告分离得到一个新的阴道毛滴虫Ras cDNA克隆,命名为TvRasC。TvRasC cDNA编码一个194氨基酸的蛋白,与其它Ras亚家族成员蛋白序列的一致性在46 %到52 %之间。序列分析表明,该蛋白序列拥有Ras亚家族保守的结合GTP结构域。进化树分析发现该基因与人类的Rit基因位于同一亚群。由于Rit家族成员不含有CAAX异戊烯化基序,而TvRasC在羧基末端有一个典型的CAAX异戊烯化基序,因此TvRasC不属于Rit家族成员。在TvRasC的效应结构域内,与位于HRas第33位的天冬氨酸对应的氨基酸残基是天冬酰胺,有研究表明这种变化将大大削弱Ras基因家族与下游效应分子Raf的结合能力。因此我们预测TvRasC可能只有低水平的GTP酶活性,这种替换有可能使Raf失去与Ras结合域相互作用,并可能导致有活性有丝分裂蛋白激酶没有刺激效应。有关TvRasC在寄生性阴道毛滴虫原虫中的作用有待进一步研究。

The Ras superfamily of GTP binding proteins encompasses a wide range of family members, related by conserved amino-acid motifs, and act as molecular binary switches that play key roles in cellular processes. We have identified a novel Ras homologue cDNA of Trichonmonas vagirtalis, TvRasC. The TvRasC cDNA encodes a 194 amino acid protein that shares 46% - 52% overall identity with other members of Ras subfamily. Sequence analysis showed the amino acid residues of TvRasC contain five G box domains that designate it as a Ras subfamily. Phylogenetic analysis showed TvRasC and human Rit can be classified into a subgroup of the Ras family. However, TvRasC could not be a member of Rit homologue because it has a typical CAAX prenylation motif at the carboxyl-terminal, and Rit is a member of Ras-like protein without CAAX prenylation motif. Within the effector domains, TvRasC has Asn at a position corresponding to Asp-33 in HRas, which impairs its interaction with the downstream effector Raf. So we predicted that TvRasC may have only a low level of GTPase activity and fail to interact with the Ras-binding domain of Raf. This may result in no stimulation of mitogen activated protein kinase. Further function of TvRasC in regulating cellular signal transduction pathways of the parasitic protist T. vaginalis remains to be studied.