Fukada Y, Takao T, Ohguro H, Yoshizawa T, Akino T, Shimonishi Y
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Nature. 1990 Aug 16;346(6285):658-60. doi: 10.1038/346658a0.
Transducin, composed of subunits T alpha, T beta and T gamma, is a member of a heterotrimeric G-protein family, and transduces the light signal in visual cells. We have recently found that bovine T beta gamma can be separated into two components. T beta gamma-1 and T beta gamma-2, each of which has its own gamma-subunit, T gamma-1 and T gamma-2, respectively. T beta gamma-2 enhances the binding of GTP to T alpha in the presence of metarhodopsin II by about 30-fold compared with T beta gamma-1. Here we show that a farnesyl moiety is attached to a sulphur atom of the C-terminal cysteine of T gamma-2 (active form), a part of which is additionally methyl-esterified at the alpha-carboxyl group. In T gamma-1 (inactive form), however, such modifications are missing. Thus, the farnesyl moiety attached to the gamma-subunit is indispensable for the GTP-binding activity of transducin. This suggests that a similar modification may occur in the gamma-subunits of other heterotrimeric G proteins involved in biological signal transduction processes.
转导素由Tα、Tβ和Tγ亚基组成，是异源三聚体G蛋白家族的成员，在视觉细胞中传导光信号。我们最近发现，牛Tβγ可分为两个组分，即Tβγ-1和Tβγ-2，它们分别有自己的γ亚基，即Tγ-1和Tγ-2。与Tβγ-1相比，在视紫红质II存在的情况下，Tβγ-2可使GTP与Tα的结合增强约30倍。在此我们表明，法尼基部分连接到Tγ-2（活性形式）C末端半胱氨酸的硫原子上，其一部分在α羧基处还额外进行了甲酯化。然而，在Tγ-1（无活性形式）中不存在这种修饰。因此，连接到γ亚基上的法尼基部分对于转导素的GTP结合活性是必不可少的。这表明，在参与生物信号转导过程的其他异源三聚体G蛋白的γ亚基中可能会发生类似的修饰。
