G Protein γ Subunits Provide Functional Selectivity

N. Eckardt
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引用次数: 1

Abstract

Heterotrimeric G protein signaling mediated by transmembrane G protein–coupled receptors (GPCRs) is ubiquitous among eukaryotes. The G protein heterotrimer consists of α, β, and γ subunits bound to specific GPCRs. Ligand binding to the GPCR induces a change in Gα and the exchange of bound GDP for GTP, which turns the Gα subunit and the Gβγ dimer into two functional signaling units. Intrinsic GTPase activity of Gα returns the heterotrimer back to the inactive form. Diversity and selectivity in G protein signaling in mammals is provided by the existence of gene families for each of the G protein subunits. Humans contain at least 23 Gα subunits, 6 Gβ subunits, and 12 Gγ subunits, which show selectivity in their interactions and differences in tissue specificity. By contrast, Arabidopsis and a number of other plants contain one Gα subunit, one Gβ subunit, and two Gγ subunits (some legumes have two Gα subunits). Evidence is emerging that Gα and Gβγ are involved in signaling in specific and independent pathways in plants. Trusov et al. (pages 1235–1250) show that the two Gγ subunits in Arabidopsis provide functional selectivity to Gβγ signaling. Genetic analyses reveal that the two Gγ subunits provide specificity to the Gβγ dimer action in at least three different signaling pathways: fungal resistance, glucose sensing, and auxin-mediated lateral root development. Figure 1 Distinct patterns of expression of the two Gγ genes, AGG1 and AGG2, in root tissue, relative to expression of AGB1, which encodes the Gβ subunit.
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G蛋白γ亚基提供功能选择性
跨膜G蛋白偶联受体介导的异三聚体G蛋白信号在真核生物中普遍存在。G蛋白异源三聚体由α、β和γ亚基结合到特定的gpcr上。与GPCR结合的配体诱导Gα的变化和GTP的交换,从而使Gα亚基和Gβγ二聚体成为两个功能信号单位。Gα的内在GTPase活性使异源三聚体回到无活性形式。哺乳动物G蛋白信号的多样性和选择性是由每个G蛋白亚基的基因家族的存在提供的。人类含有至少23个Gα亚基,6个Gβ亚基和12个Gγ亚基,它们在相互作用中表现出选择性和组织特异性的差异。相比之下,拟南芥和许多其他植物含有一个Gα亚基,一个Gβ亚基和两个Gγ亚基(一些豆科植物有两个Gα亚基)。越来越多的证据表明,Gα和Gβγ参与了植物中特定和独立的信号通路。Trusov等人(1235-1250页)表明,拟南芥中的两个Gγ亚基对Gβγ信号传导具有功能选择性。遗传分析表明,两个Gγ亚基在至少三种不同的信号通路中为Gβγ二聚体的作用提供特异性:真菌抗性、葡萄糖感应和生长素介导的侧根发育。图1相对于编码Gβ亚基的AGB1的表达,根组织中两个Gγ基因AGG1和AGG2的表达模式不同。
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