美国宾夕法尼亚大学生物系208 Mueller实验室，Donald Danforth植物科学研究中心，威斯康辛大学生物技术中心无生物化学系的研究者近期在拟南芥中发现两种新型的GPCR型G蛋白是脱落酸受体（Abscisic Acid Receptors ，ABA）。
在植物中，G蛋白通过应激激素（stress hormone）和脱落酸（abscisic acid，ABA）调节信号。研究者以拟南芥为模型鉴定出两种新的拟南芥蛋白，并对这两种蛋白的特征进行了分析研究，研究发现两种新的蛋白与orphan vertebrate GPCR（GPR89）同源，并能与sole 拟南芥G蛋白α亚单位GPA1相互作用，两种蛋白具有内部的GTP结合位点，并具有GTP酶活性。
研究者将两种新发现的酶命名为GPCR-type G Protein（GTG1和GTG2）。拟南芥突变株缺乏GTG1和GTG2表现出对脱落酸（ABA）低敏感性。GTG1和GTG2能与脱落酸特异性结合。GTGs内GDP结构域同GTGs内GTP结构域相比展现出对脱落酸强大结合能力，GTGs的GTP酶活性受GPA1抑制，并且gpa1无效突变体表现出对脱落酸具有高度敏感性。
这些结果表明，GDP结构比GTP结构更具有信号传递活性。研究者推测，GTG蛋白不仅是一种新型的G蛋白，还是一类细胞膜脱落酸受体。（生物谷Bioon.com）
生物谷推荐原始出处：
Cell, Volume 136, 9 January 2009 doi:10.1016/j.cell.2008.12.026
Two Novel GPCR-Type G Proteins Are Abscisic Acid Receptors in Arabidopsis
Sona Pandey1,2,David C. Nelson3,4andSarah M. Assmann1,,
1 Biology Department, 208 Mueller Laboratory, Penn State University, University Park, PA 16802, USA
2 Donald Danforth Plant Science Center, St. Louis, MO 63132, USA
3 Biotechnology Center and Biochemistry Department, University of Wisconsin, 425 Henry Mall, Madison, WI 53706, USA
4 Present address: Plant Energy Biology, University of Western Australia, 35 Stirling Highway, Crawley 6009 WA, Australia
Summary
In plants, G proteins modulate signaling by the stress hormone, abscisic acid (ABA). We identify and characterize two novel Arabidopsis proteins that show homology to an orphan vertebrate GPCR (GPR89) and interact with the sole Arabidopsis G protein subunit, GPA1, but also have intrinsic GTP-binding and GTPase activity. We have named these proteins GPCR-type G proteins (GTG1 and GTG2). Arabidopsis mutants lacking both GTG1 and GTG2 exhibit ABA hyposensitivity. GTG1 and GTG2 bind ABA specifically. The GDP-bound form of the GTGs exhibits greater ABA binding than the GTP-bound form, the GTPase activity of the GTGs is inhibited by GPA1, and gpa1 null mutants exhibit ABA-hypersensitive phenotypes. These results predict that, unusually, it is the GDP-bound, not the GTP-bound, form of the GTGs that actively relays the signal. We propose that GTG proteins function both as a new type of G protein and as a class of membrane-localized ABA receptors.
