Ong O C, Yamane H K, Phan K B, Fong H K, Bok D, Lee R H, Fung B K
Jules Stein Eye Institute, UCLA School of Medicine 90024, USA.
J Biol Chem. 1995 Apr 14;270(15):8495-500. doi: 10.1074/jbc.270.15.8495.
The phototransduction process in cones has been proposed to involve a G protein that couples the signal from light-activated visual pigment to the effector cyclic GMP phosphodiesterase. Previously, we have identified and purified a G beta gamma complex composed of a G beta 3 isoform and an immunochemically distinct G gamma subunit (G gamma 8) from bovine retinal cones (Fung, B. K.-K., Lieberman, B. S., and Lee, R. H. (1992) J. Biol. Chem. 267, 24782-24788; Lee, R. H., Lieberman, B.S., Yamane, H. K., Bok, D., and Fung, B. K.-K. (1992a) J. Biol. Chem. 267, 24776-24781). Based on the partial amino acid sequence of this cone G gamma 8, we screened a bovine retinal cDNA library and isolated a cDNA clone encoding G gamma 8. The cDNA insert of this clone includes an open reading frame of 207 bases encoding a 69-amino acid protein. The predicted protein sequence of G gamma 8 shares a high degree of sequence identity (68%) with the G gamma (G gamma 1) subunit of rod transducin. Similar to rod G gamma 1, it terminates in a CIIS motif that is the site for post-translational modification by farnesylation. Messenger RNA for G gamma 8 is present at a high level in the retina and at a very low level in the lung, but is undetectable in other tissues. Immunostaining of bovine retinal sections with an antipeptide antibody against the N-terminal region of G gamma 8 further shows a differential localization of G gamma 8 to cones with a pattern indistinguishable from that of G beta 3. This finding suggests that G beta 3 gamma 8 is a component of cone transducin involved in cone phototransduction and color vision.
有人提出，视锥细胞中的光转导过程涉及一种G蛋白，该蛋白将来自光激活视觉色素的信号与效应器环鸟苷酸磷酸二酯酶偶联。此前，我们已从牛视网膜视锥细胞中鉴定并纯化出一种由Gβ3亚型和一种免疫化学上不同的Gγ亚基（Gγ8）组成的Gβγ复合物（冯，B.K.-K.，利伯曼，B.S.，和李，R.H.（1992年）《生物化学杂志》267卷，24782 - 24788页；李，R.H.，利伯曼，B.S.，山根，H.K.，博克，D.，和冯，B.K.-K.（1992a年）《生物化学杂志》267卷，24776 - 24781页）。基于这种视锥细胞Gγ8的部分氨基酸序列，我们筛选了一个牛视网膜cDNA文库，并分离出一个编码Gγ8的cDNA克隆。该克隆的cDNA插入片段包含一个207个碱基的开放阅读框，编码一个69个氨基酸的蛋白质。预测的Gγ8蛋白序列与视杆细胞转导素的Gγ（Gγ1）亚基具有高度的序列同一性（68%）。与视杆细胞Gγ1类似，它以一个CIIS基序结尾，该基序是法尼基化进行翻译后修饰的位点。Gγ8的信使RNA在视网膜中高水平存在，在肺中非常低水平存在，但在其他组织中无法检测到。用针对Gγ8 N端区域的抗肽抗体对牛视网膜切片进行免疫染色，进一步显示Gγ8在视锥细胞中的定位差异，其模式与Gβ3无法区分。这一发现表明Gβ3γ8是参与视锥细胞光转导和色觉过程的视锥细胞转导素的一个组成部分。
