mineral nutrients, organic metabolites, growth regulators and hormones. Signals can vary in quality and quantity from minute to minute. Some of the signals are carried by xylem and phloemthe circulatory system, which can accommodate very large and rapid fluxes. Once a cell picks up a chemical or physical signal, it must transmit this information from the surface to the interior parts of the cell 第三节跨膜信号传递 Transmembrane signal transduction G-蛋白介导跨膜信号传递的过程 信号分子与它相应的受体结合只是信号传递的第一步。信息必须通过跨膜传递到 达细胞内部。我们以G-蛋白参与信号传递为例来说明信号是如何实现跨膜传递 的。G-蛋白是GTP水解酶大家族的一个亚家族,异源三聚体G蛋白含有三种亚基 (α、β、γ)。在信号的跨膜传递过程中,G-蛋白和它所结合GTP进行着周期性 的变化。G-蛋白处于非活化状态时,与GDP结合;处于活化状态时,与GTP结合。 异源三体G蛋白以非活化状态位于膜内侧靠近受体处,三个亚基结合在一起。当 某种刺激信号与其膜上的特异受体结合后,激活的受体将信号传递给G蛋白,G 蛋白的α亚基结合GTP替换原来的GDP。活化的a亚基与β和γ亚基复合体分离 继而触发效应器,把胞外信号转换成胞内信号。α亚基与效应器相互作用后即水 解它所结合的GTP从而转变为非活性状态,重新与与β和γ亚基结合。信号在G 蛋白的循环过程得以放大,因为一个活化的G-蛋白能激活无数个效应器。 Process of G-protein mediated transmembrane signal transduction The binding of a signal to its cognate receptor is only the beginning of the signaling process. The information has to be conveyed across the plasma membrane to get inside the cell. We will take the involvement of G-protein in signal transduction pathway as an example to explain the transmembrane transduction processes G-proteins are a special subset of a GTPase superfamily. Hetertrimeric G-proteins are composed of three subunits(a, B and y). During the process of transmembrane signal transduction, heterotrimeric G-proteins undergo a modified cycle with GTP G-protein binds GDP when it is inactive, when active, it binds GTP. The G protein normally lies near the receptor in an inactive state with 3 subunits bound together When the receptor gets activated by ligand binding, it will rapidly bind to the g protein, causes the release of GDP from the a-subunit and its replacement by GTP Once this happens, the G-protein loses affinity for the receptor, dissociates from it, the activated a-subunit also dissociate from B-and y-subunits of the G-protein, and moves over and interact with its target protein, the information from outside a cell is thus conveyed into the cell. After encounter with its target protein, the alpha subunit of the G protein will hydrolyze its bound GTP, thereby reverting to an inactive state. It will then rejoin the beta and gamma subunits. Signal amplification is inherent in the G-protein cycle because one activated G-protein can interact with and activate numerous target proteins G-蛋白在植物细胞信号传递中的作用 植物G蛋白的研究始于20世纪80年代。实验数据显示G蛋白参与蓝光,红光,生mineral nutrients, organic metabolites, growth regulators and hormones. Signals can vary in quality and quantity from minute to minute. Some of the signals are carried by xylem and phloemthe circulatory system, which can accommodate very large and rapid fluxes. Once a cell picks up a chemical or physical signal, it must transmit this information from the surface to the interior parts of the cell 第三节 跨膜信号传递 Transmembrane signal transduction G-蛋白介导跨膜信号传递的过程 信号分子与它相应的受体结合只是信号传递的第一步。信息必须通过跨膜传递到 达细胞内部。我们以G-蛋白参与信号传递为例来说明信号是如何实现跨膜传递 的。G-蛋白是GTP水解酶大家族的一个亚家族，异源三聚体G蛋白含有三种亚基 (α 、β 、γ )。在信号的跨膜传递过程中，G-蛋白和它所结合GTP进行着周期性 的变化。G-蛋白处于非活化状态时，与GDP结合；处于活化状态时，与GTP结合。 异源三体G蛋白以非活化状态位于膜内侧靠近受体处，三个亚基结合在一起。当 某种刺激信号与其膜上的特异受体结合后，激活的受体将信号传递给G蛋白，G 蛋白的α亚基结合GTP替换原来的GDP。活化的α 亚基与β 和γ 亚基复合体分离， 继而触发效应器，把胞外信号转换成胞内信号。α 亚基与效应器相互作用后即水 解它所结合的GTP从而转变为非活性状态，重新与与β 和γ 亚基结合。信号在G- 蛋白的循环过程得以放大，因为一个活化的G-蛋白能激活无数个效应器。 Process of G-protein mediated transmembrane signal transduction The binding of a signal to its cognate receptor is only the beginning of the signaling process. The information has to be conveyed across the plasma membrane to get inside the cell. We will take the involvement of G-protein in signal transduction pathway as an example to explain the transmembrane transduction processes. G-proteins are a special subset of a GTPase superfamily. Hetertrimeric G-proteins are composed of three subunits ( and ). During the process of transmembrane signal transduction, heterotrimeric G-proteins undergo a modified cycle with GTP. G-protein binds GDP when it is inactive; when active, it binds GTP. The G protein normally lies near the receptor in an inactive state with 3 subunits bound together. When the receptor gets activated by ligand binding, it will rapidly bind to the G protein, causes the release of GDP from the α-subunit and its replacement by GTP. Once this happens, the G-protein loses affinity for the receptor, dissociates from it, the activated α-subunit also dissociate from β- and γ-subunits of the G-protein, and moves over and interact with its target protein, the information from outside a cell is thus conveyed into the cell. After encounter with its target protein, the alpha subunit of the G protein will hydrolyze its bound GTP, thereby reverting to an inactive state. It will then rejoin the beta and gamma subunits. Signal amplification is inherent in the G-protein cycle because one activated G-protein can interact with and activate numerous target proteins. G-蛋白在植物细胞信号传递中的作用 植物G蛋白的研究始于20世纪80年代。实验数据显示G-蛋白参与蓝光，红光，生