异三聚体G蛋白调控植物生长发育功能研究进展北大核心CSCD

异三聚体GTP结合蛋白(G蛋白)是介导真核生物生长发育及逆境响应的关键信号传导组分。动物和植物异三聚体G蛋白由α、β、γ三个亚基组成。近来研究表明,尽管G蛋白核心组分和基本的生化性质在动物和植物中保守,但植物G蛋白表现出新的调控模式。由于G蛋白参与调控植物种子产量、器官大小、生物和非生物胁迫、氮素利用效率等一系列重要的农艺性状,因此对于G蛋白的研究已经成为植物学领域的研究热点。该文对近年来国内外有关植物异三聚体G蛋白的基本组成及结构、动植物G蛋白的作用模式以及G蛋白在植物生长发育过程中的调控作用和植物在逆境胁迫(干旱、温度和盐)响应中的功能等方面的研究进展进行综述,为今后开展植物G蛋白的相关研究提供参考以及为利用G蛋白改良农作物提供理论基础。     

β-TC3细胞膜与胰岛素受体结合G蛋白的鉴定

目的:用免疫共沉淀的方法检测β-TC3(小鼠胰岛β细胞瘤细胞)细胞膜中与胰岛素受体结合的G蛋白.方法:提取β-TC3细胞膜蛋白,通过免疫共沉淀及蛋白质印迹的方法,检测G蛋白α及β亚基的表达.结果:抗胰岛素受体抗体沉淀胰岛素受体结合的G蛋白复合物后,分别用抗胰岛素受体抗体、抗G蛋白α亚基抗体及抗G蛋白β亚基抗体,检测到胰岛素受体、G蛋白α亚基及G蛋白β亚基的表达.结论:在β-TC3细胞膜中,胰岛素受体与G蛋白共存,G蛋白α亚基及β亚基与胰岛素受体可能存在直接的相互作用.     

G蛋白与受体的信息传递

一、引言G 蛋白又称 GTP 结合蛋白、鸟苷酸调节蛋白、N 蛋白、G/F 蛋白等,10年前人们对它还一无所知。在研究受体激活腺苷酸环化酶(AC)的作用机理时,发现 G 蛋白是受体和 AC 之间独立的、功能与二者密切相关的蛋白质,存在于细胞膜脂质双分子层。近年来,随着对 G 蛋白的研究,揭开了许多受体作用之谜,G蛋白的重要作用愈加受到重视。本刊1986年曾综述了 G 蛋白对 AC 的调节作用。本文就 G 蛋白的基本生化特性及其生理功能,结合1986～1987年的最新进展,作一较系统的论述。     

真菌G蛋白信号调控蛋白的功能研究进展

G蛋白信号途径是真菌细胞信号转导网络的枢纽,在细胞的各种生物学调控过程中具有重要作用。G蛋白信号调控蛋白(Rgulators of G protein signaling,RGS)是一类重要的G蛋白信号调控因子,能通过促进G蛋白α亚基(Gα)偶联的GTP水解,使Gα和Gβγ亚基发生聚合,导致G蛋白失活,从而迅速关闭与G蛋白偶联的信号途径。自从第一个RGS蛋白在酿酒酵母中被鉴定以来,目前已经有30多个RGS蛋白在重要的模式真菌中被报道,包括构巢曲霉、绿僵菌、稻瘟病菌、玉米赤霉菌、轮枝镰孢菌、新型隐球菌和白色念珠菌等。RGS蛋白在真菌的营养菌丝生长、产孢、毒素和色素生产、致病性和有性生殖等过程中发挥着重要作用。本文对真菌中已报道RGS蛋白的功能进行了总结,对真菌RGS蛋白的结构特征和调控机制进行了评述。     

细胞外钙受体相互作用蛋白的研究进展

细胞外钙受体(CaR)为G蛋白偶联受体超家族中的成员,它的大部分作用是以Gαi,Gαq和Gα12/13为中介的,但由G蛋白α亚基介导的作用并不能完全解释CaR的生物学效应.与CaR相互作用蛋白如抑制蛋白、G蛋白受体激酶、受体激活修饰蛋白、丝蛋白、钾通道、小窝蛋白等结构和信号蛋白赋予CaR独特的信号转导特征,并能够更充分说明CaR在不同组织和细胞中所发挥的作用.本文将对上述几种与其相互作用蛋白及它们所产生的生物学效应做一综述.     

AGS3蛋白与G蛋白信号转导

AGS3蛋白是影响受体到G蛋白的信号转导或直接影响非受体依赖型G蛋白激活的蛋白质之一。AGS3蛋白在脑、睾丸、肝脏、肾脏、心脏、胰腺及PC-12细胞中普遍分布。它不仅具有不依赖受体的Gβγ信号转导激活物的作用,也能作为二磷酸乌苷（GDP）的解离抑制剂,并负向调节G蛋白偶联受体对G蛋白的激活。AGSl、AGS2、AGS4是AGS家族的其它几个成员,能选择性激活不同类型的G蛋白。LGN和PINS蛋白是AGS3的同系物。AGS3蛋白与信号转导的关系是目前研究的热点之一。     

植物G蛋白与植物防卫反应

近年来, 植物G蛋白(包括异三聚体G蛋白和小G蛋白)的存在及其信号调控途径已经成为人们研究细胞信号转导过程的热点问题。从多种植物细胞中相继分离克隆出多个与动物G蛋白同源的编码植物G蛋白的基因, 并且植物G蛋白的种类和数量有其独特性。植物G蛋白在植物细胞跨膜信号转导中发挥重要的作用, 参与多种生命活动的调控。本文主要综述了植物G蛋白参与植物防卫反应调节作用的研究进展。     

Rho小G蛋白介导的细胞周期调控

Rho小G蛋白作为一个信号分子家族具有多样化的功能, 可以调节细胞骨架重排 、细胞迁移、细胞极性、基因表达、细胞周期调控等. Rho小G蛋白家族对细胞周期 调控的研究主要集中在其对于有丝分裂期细胞的调节作用,包括调节有丝分裂期前 期细胞趋圆化、后期染色体排列及收缩环的收缩作用.近期的研究显示,Rho小G蛋白及其效应分子对于细胞周期G1、S、G2期的调控主要是通过影响细胞周期的正调控因子细胞周期蛋白D1 (cyclin D1) 和负调控因子细胞周期蛋白依赖型激酶相互作用蛋白1及细胞周期蛋白依赖型激酶抑制蛋白27 (p21cip1/p27kip1) 进行的.本文总结了Rho小G蛋白及其效应分子在细胞周期调控,尤其是对G1/S期调控的研究进展,并简要阐述了Rho小G蛋白介导的细胞周期调控异常与癌症发生的关系.     

与阿尔兹海默症相关的G 蛋白偶联受体研究进展

G蛋白偶联受体(GPCRs)在大脑信号传递中至关重要,而在阿尔兹海默症(AD)中,G蛋白偶联受体通过调控α-、β-及γ-分泌酶分泌、淀粉样前体蛋白(APP)生成及β-淀粉样蛋白(Aβ)降解,直接影响β-淀粉样蛋白在神经系统信号级联反应;另外,阿尔兹海默症中β-淀粉样蛋白的生成可以扰乱G蛋白偶联受体功能.因此,阐明G蛋白偶联受体与阿尔兹海默症发病之间的关联有助于开发以G蛋白偶联受体为靶点的阿尔兹海默症治疗药物.     

G蛋白信号调节因子的结构分类和功能

G蛋白信号调节因子是能够直接与激活的Gα亚基结合,显著刺激Gα亚基上的GTP酶活性,加速GTP水解,从而灭活或终止G蛋白信号的一组分子大小各异的多功能蛋白质家族。它们都共同拥有一个130个氨基酸的保守的RGS结构域,其功能是结合激活的Gα亚基,负调节G蛋白信号。许多RGS蛋白还拥有非RGS结构域,能够结合其它信号蛋白,从而整合和调节G蛋白信号之间以及G蛋白和其它信号系统之间的关系。     

心脏疾病中G蛋白的变化

G蛋白是一类重要的信号转导分子,其生理功能是将细胞膜受体所识别的各种细胞外信号同细胞内一系列效应分子偶联起来,引起核基因转录及蛋白质结构和功能的变化。G蛋白在心脏表达的亚型有Gs、Gi/o、Gq／11、G12／13,参与心肌收缩力、心率、心律和心肌细胞生长的调节。本文着重讨论了心脏G蛋白的分类、结构和功能,以及在心肌肥大、心力衰竭、急性心肌缺血和心律失常等心脏疾病中的改变,以加深对这些疾病的发病机制和病理生理过程的认识。     

G蛋白及其偶联信号传导途径的研究进展

G蛋白偶联信号传导系统是一类重要的细胞跨膜信号传导途径之一。在有关生化及药理的医学研究中发现许多药剂都是通过G蛋白偶联信号传导途径对动物起作用的。对G蛋白结构与功能的系统研究是新型药剂研制与开发的基础。G蛋白在物种进化过程中具有高度保守性,植物和昆虫中的G蛋白及其偶联组份研究将有助于明确作物抗病虫机理以及昆虫毒理。     

丝状真菌G蛋白信号途径的研究进展

丝状真菌在工业、农业、医药等领域具有重要经济价值,一些亦可导致人类及动、植物疾病,造成经济损失.G蛋白信号途径是真核生物中普遍存在的细胞跨膜信号转导途径.近年来,丝状真菌中G蛋白信号途径的研究发展很快,相关报道表明该信号途径参与感应并传递多种胞外信号刺激,对丝状真菌的生长、分化、繁殖、致病性及真菌毒素等次生代谢产物合成有重要的调控作用.本文就丝状真菌中G蛋白信号途径的基本组成及其生理功能的研究现状进行简要综述.     

The guanine nucleotide-binding regulatory proteins (G proteins) in myocardium with ischemia

Guanine nucleotide-binding regulatory proteins (G proteins) play a major role in the regulation of a number of physiological processes, such as stimulation or Inhibition of adenylate cyclase activity or gaiting of ionic channels. Myocardial ischemia could induce the changes in receptor-G protein signal transduction system in the heart. Therefore, this article will focus on the role and alterations of G proteins (especially, Gs and Gi) in myocardial ischemia. The Gi protein rapidly loses functional activity during very early myocardial ischemia. In contrast to Gi protein, the function of Gs protein during this phase has not been evaluated. Moreover, the changes in Gs protein after 30 min of ischemia are contradictory. However, the sensitization of the adenylate cyclase activity in the very early phase of acute ischemia is gradually replaced by a decrease in adenylate cyclase activity with prolonged ischemia. The decrease in the function and amount of Gs protein may be one of the factors that induce these changes. The function of Gs protein was also decreased in the canine hearts with ischemia and reperfusion. In contrast to ischemia and reperfusion, there are no significant alterations in G proteins and modulation of adenylate cyclase in the stunned myocardium. It has become increasingly evident that Gi protein may play an important role in the cardioprotective effects of preconditioning. When -adrenoceptor densities are reduced in chronic myocardial ischemia, decreased in the amount and function of Gi protein and increased amount of Gs protein may play the role in preservation of the adenylate cyclase activity. These alterations in G proteins may play the important role in the myocardial function during myocardial ischemia.     

G protein activation is prerequisite for functional coupling between Galpha/Gbetagamma and tubulin/microtubules

Heterotrimeric G proteins participate in signal transduction by transferring signals from cell surface receptors to intracellular effector molecules. Interestingly, recent results suggest that G proteins also interact with microtubules and participate in cell division and differentiation. It has been shown earlier that both alpha and betagamma subunits of G proteins modulate microtubule assembly in vitro. Since G protein activation and subsequent dissociation of alpha and betagamma subunits are necessary for G proteins to participate in signaling processes, here we asked if similar activation is required for modulation of microtubule assembly by G proteins. We reconstituted Galphabetagamma heterotrimer from myristoylated-Galpha and prenylated-Gbetagamma, and found that the heterotrimer blocks Gi1alpha activation of tubulin GTPase and inhibits the ability of Gbeta1gamma2 to promote in vitro microtubule assembly. Results suggest that G protein activation is required for functional coupling between Galpha/Gbetagamma and tubulin/microtubules, and supports the notion that regulation of microtubules is an integral component of G protein mediated signaling.     

Diverse β subunits of heterotrimeric G proteins are present in thyroid plasma membranes

The functioning of heterotrimeric G protein α subunits in the transduction of hormonal signals to appropriate intracellular responses is well recognized. Much less is known about the distribution of isoforms and functions of G protein β subunits. Here, using specific antibodies, we documented that in plasma membranes of the thyroid cell line Nthy-ori 3-1 all Gβ isoforms-Gβ₁, Gβ₂, Gβ₃, Gβ₄ and Gβ₅ are present, while the Gβ₃ occurs in minute amount. In plasma membrane fraction isolated from pooled postoperative thyroids of patients with nodular goiter and Graves’ disease, the Gβ₁, Gβ₂, Gβ₄ and Gβ₅ subunits were found, whereas Gβ₃ could not be detected.Competition studies revealed that the Gβ₂ is the principal Gβ subunit in membranes from cultured thyroid cells, originated from normal thyroid, as well as in membranes from patients’ thyroids. This suggests that Gβ₂ subunit cooperates with Gα_s subunit, the most active of the Gα variants, during stimulation of adenylate cyclase which constitutes the main route of physiological thyroid stimulation.     

G protein-coupled receptor oligomerization for what?

Although the G protein-coupled receptor (GPCR) oligomerization has been questioned during the last decade, under some premises the existence of a supramolecular organization of these receptors begins now to be widely accepted by the scientific community. Indeed, GPCR oligomers may enhance the diversity and performance by which extracellular signals are transferred to the G proteins in the process of receptor transduction, although the mechanism that underlie this phenomenon remains still unexplained. Recently, a trans-conformational switching model has been proposed as a mechanism allowing direct inhibition of receptor activation. Thus, heterotropic receptor–receptor allosteric regulations are behind the GPCR oligomeric function. Accordingly, we revise here how GPCR oligomerization impinge in several important receptor functions like biosynthesis, plasma membrane diffusion or velocity, pharmacology and signaling. Overall, the rationale of receptor oligomerization might lie in the cellular need of sensing complex extracellular signals and to translate into a simple computational mode.     

Sensing and transduction of nutritional and chemical signals in filamentous fungi: Impact on cell development and secondary metabolites biosynthesis

Filamentous fungi respond to hundreds of nutritional, chemical and environmental signals that affect expression of primary metabolism and biosynthesis of secondary metabolites. These signals are sensed at the membrane level by G protein coupled receptors (GPCRs). GPCRs contain usually seven transmembrane domains, an external amino terminal fragment that interacts with the ligand, and an internal carboxy terminal end interacting with the intracellular G protein. There is a great variety of GPCRs in filamentous fungi involved in sensing of sugars, amino acids, cellulose, cell-wall components, sex pheromones, oxylipins, calcium ions and other ligands. Mechanisms of signal transduction at the membrane level by GPCRs are discussed, including the internalization and compartmentalisation of these sensor proteins. We have identified and analysed the GPCRs in the genome of Penicillium chrysogenum and compared them with GPCRs of several other filamentous fungi. We have found 66 GPCRs classified into 14 classes, depending on the ligand recognized by these proteins, including most previously proposed classes of GPCRs. We have found 66 putative GPCRs, representatives of twelve of the fourteen previously proposed classes of GPCRs, depending on the ligand recognized by these proteins. A staggering fortytwo putative members of the new GPCR class XIV, the so-called Pth11 sensors of cellulosic material as reported for Neurospora crassa and some other fungi, were identified. Several GPCRs sensing sex pheromones, known in yeast and in several fungi, were also identified in P. chrysogenum, confirming the recent unravelling of the hidden sexual capacity of this species. Other sensing mechanisms do not involve GPCRs, including the two-component systems (HKRR), the HOG signalling system and the PalH mediated pH transduction sensor. GPCR sensor proteins transmit their signals by interacting with intracellular heterotrimeric G proteins, that are well known in several fungi, including P. chrysogenum. These G proteins are inactive in the GDP containing heterotrimeric state, and become active by nucleotide exchange, allowing the separation of the heterotrimeric protein in active Gα and Gβγ dimer subunits. The conversion of GTP in GDP is mediated by the endogenous GTPase activity of the G proteins. Downstream of the ligand interaction, the activated Gα protein and also the Gβ/Gγ dimer, transduce the signals through at least three different cascades: adenylate cyclase/cAMP, MAPK kinase, and phospholipase C mediated pathways.     

Modulation of subfamily B/R4 RGS protein function by 14-3-3 proteins

Regulator of G protein signalling (RGS) proteins are primarily known for their ability to act as GTPase activating proteins (GAPs) and thus attenuate G protein function within G protein-coupled receptor (GPCR) signalling pathways. However, RGS proteins have been found to interact with additional binding partners, and this has introduced more complexity to our understanding of their potential role in vivo. Here, we identify a novel interaction between RGS proteins (RGS4, RGS5, RGS16) and the multifunctional protein 14-3-3. Two isoforms, 14-3-3β and 14-3-3ε, directly interact with all three purified RGS proteins and data from in vitro steady state GTP hydrolysis assays show that 14-3-3 inhibits the GTPase activity of RGS4 and RGS16, but has limited effects on RGS5 under comparable conditions. Moreover in a competitive pull-down experiment, 14-3-3ε competes with Go for RGS4, but not for RGS5. This mechanism is further reinforced in living cells, where 14-3-3ε sequesters RGS4 in the cytoplasm and impedes its recruitment to the plasma membrane by G protein. Thus, 14-3-3 might act as a molecular chelator, preventing RGS proteins from interacting with G, and ultimately prolonging the signal transduction pathway. In conclusion, our findings suggest that 14-3-3 proteins may indirectly promote GPCR signalling via their inhibitory effects on RGS GAP function.