Study of the structure and the function of heterotrimeric G proteins in higher plants

植物异源三聚体G蛋白参与了植物激素、激发子和光等多种胞外信号的转导。在植物G蛋白中，亚基在细胞内的精确定位还没有被分析。在本工作中，我们分析了大米G蛋白亚基的定位。1.Western印迹分析表明，α，β，γ1和γ2亚基定位于大米质膜分级。2.经胆酸溶解的膜蛋白通过凝胶过滤(Superdex 200 PC3.2/30，SMART System，Pharmacia)进行分级。获得了两个G蛋白片段，一个是含杂三聚体(S)的大分子复合体(400 kDa复合体)，另一个是βγ二聚体(S)(60 KDa)。我们认为，在水稻植株的质膜中，大量的βγ二聚体以不存在α亚单位的形式存在。3.在质膜组分中定位了一个具有固有活性的亚单位(QL)。当含有QL的膜组分被溶解和凝胶过滤分级时，QL存在于60 kDa的组分中。这一结果表明，α亚基的活性形式可能与杂三聚体解离。

Plant heterotrimeric G proteins have been proposed to be involved in the transduction of several extracellular signals such as plant hormones, elicitor and light. In the plant G proteins, the precise intracellular localization of the subunits have not yet been analyzed. In the present work, we analyzed the localazation of the subunits of the rice G protein.1.Western blot analysis showed that the α, β, γ1 and γ2 subunits were localized in rice plasma membrane fractions.2.Membrane-proteins solubilized with cholate were fractionated by gel filtration (Superdex 200 PC3.2/30, SMART System, Pharmacia). Two fractions of the G protein were obtained ; one seemed to be large complexes (400 kDa complexes) containing heterotrimer(s) and the other, βγ dimmer(s) (60 kDa). We propose that, in rice plants, a large amount of βγ dimmer is present in the plasma membrane in a form without the αsubunit.3.Constitutively active a subunit (QL) was localized in plasma membrane fractions. When membrane fractions containing QL were solubilized and fractionated by gel filtration, QL was present in 60 kDa fractions. This result shows that the active form of the α subunit may dissociate from the heterotrimer.