G蛋白

Ｇ蛋白是一类含鸟苷酸的蛋白质,存在于细胞外膜内表面,为生物信息转导过程中关键的中介体,可以决定信号传输通路何时打开和关闭。介绍Ｇ蛋白的基本结构和作用模式。     

G蛋白家族

鸟嘌呤核苷酸结合蛋白(G 蛋白)结构和功能的进一步阐明是80年代细胞膜分子生物学研究的最新进展之一。G 蛋白广泛参与细胞膜腺苷酸环化酶活性兴奋与抑制的双重控制、视网膜视杆细胞的光导作用,以及与蕈毒碱受体功能有关的多种生理生化过程。     

实时逆转录PCR检测G1、G2和G4型轮状病毒方法的建立

目的建立3种用于检测G1、G2和G4型轮状病毒VP7基因的一步法实时逆转录PCR,用于本实验室G1、G2和G4型轮状病毒的快速检测和定量、定性分析。方法设计G1、G2和G4型轮状病毒VP7基因特异性引物和探针,采用G1、G2和G4型轮状病毒特异性体外转录RNAs,建立实时逆转录PCR,特异性检测G1、G2和G4型轮状病毒VP7基因方法。结果 3种实时逆转录PCR标准曲线R~2均大于0.99,扩增效率均在90%～110%之间。不同浓度体外转录RNAs重复性检测结果 CV均5%,且可以对单拷贝RNAs样本进行检测。结论本检测方法快速、灵敏且重复性好,可以对轮状病毒VP7基因进行特异而有效的检测,为实验室轮状病毒毒株的分型和定量检测提供了特异而有效的检测方法,也为今后多重实时逆转录PCR的建立奠定了试验基础。     

Pasteurella multocida toxin activates Gβγ dimers of heterotrimeric G proteins

The mitogenic Pasteurella multocida toxin (PMT) is a major virulence factor of P. multocida, which causes Pasteurellosis in man and animals. The toxin activates the small GTPase RhoA, the MAP kinase ERK and STAT proteins via the stimulation of members of two G protein families, G_q and G_12/13. PMT action also results in an increase in inositol phosphates, which is due to the stimulation of PLCβ via Gα_q. Recent studies indicate that PMT additionally activates Gα_i to inhibit adenylyl cyclase. Here we show that PMT acts not only via Gα but also through Gβγ signaling. Activation of Gβγ by PMT causes stimulation of phosphoinositide 3-kinase (PI3K) γ and formation of phosphatidylinositol-3,4,5-trisphosphate (PIP₃) as indicated by the recruitment of a PIP₃-binding pleckstrin homology (PH) domain-containing protein to the plasma membrane. Moreover, it is demonstrated that Gβγ is necessary for PMT-induced signaling via Gα. Mutants of Gα_q incapable of binding or releasing Gβγ are not activated by PMT. Similarly, sequestration of Gβγ inhibits PMT-induced Gα-signaling.     

线粒体小分子G蛋白

近年来,在线粒体上发现一类G蛋白,属于一类单体小分子GTP结合蛋白家族。该类蛋白质的主要作用可能参与线粒体膜融合,因而可能对线粒体的生理过程发挥重要的调节作用。目前认为,线粒体小分子G蛋白可能通过介导膜融合方式参与线粒体蛋白质的转运、类固醇激素的合成,以及精子生成等过程。     

G蛋白偶联受体与G蛋白相互作用的最新研究进展

传统观念认为,在激动剂作用下,G蛋白偶联受体(GPCRs)能够激活G蛋白的α亚基,从而使Gα亚基与Gβγ亚基分离,被激活的Gα亚基通过信号转导进一步参与细胞的生理过程。但是,最新研究发现GPCRs和G蛋白存在多种偶联关系,GPCRs不仅能够激活Gα亚基,还可以与Gβγ亚基相互靠近,甚至会使G蛋白亚基构象发生重排而不分离,这对于疾病发病机制的研究及新的药物靶点的发现具有重要意义。就GPCRs与G蛋白之间的相互作用以及最新研究技术作一简要综述。     

孟氏裂头绦虫染色体G分带和G带定量分析

本文应用胰酶法对孟氏裂头绦虫染色体作G分带研究,获得比较清晰的G带带纹。并运用显微分 光光度计对G带带纹进行了扫描定量分析。     

豚鼠特工G势力

<正>豚鼠?特工?这两者会有联系吗?没错。在风靡全球的电影《豚鼠特工队》中,几只个头小小的豚鼠精英就展示了它们的无敌风采,让那些认为豚鼠只是可爱宠物的人连连惊呼:哇哦,豚鼠特工,真酷!     

G蛋白直接影响离子通道

G蛋白的经典作用一般认为是对第二信使物质的代谢酶进行调节,如Gs可激活腺苷酸环化酶(AC),Gi抑制AC,Gt激活cGMP依赖的磷酸二脂酶,通过第二信使系统影响离子的跨膜流动。最近有人提出,G蛋白可直接作用于离子通道。     

HLA—G研究进展

ＨＬＡ－Ｇ分子属ＭＨＣ Ⅰ类非典型分子（ＭＨＣ Ⅰｂ）组织特异性地高表达于胎母界面的滋养层细胞,ＭＨＣⅠ、Ⅱ类抗原是缺乏的,ＨＬＡ－Ｇ分子通过ＮＫ细胞受体抑制ＮＫ细胞杀伤性,并作为ＣＤ８＾＋细胞毒抑制性Ｔ细胞的识别和激活因子,抑制ＣＴＬ的杀伤作用,ＨＬＡ－Ｇ在胎母耐受中发挥重要作用。     

蛋白酶水解免疫球蛋白G

三十年前就已开始用蛋白酶消化免疫的马血浆,以获得精制高效的破伤风和白喉抗毒素。这一方法目前仍是制备各种精制抗毒素的良好手段。近二十年来由于蛋白质分离技术的进展,对进一步了解免疫球蛋白的结构、功能和遗传性提供了有利的条件。 Porter(1959)首先用木瓜酶水解家兔抗体免疫球蛋白GIgG得到两种碎片,一为Fab(F代表碎片,ab代表能与抗原相结合的抗体部分),另一为Fc(c表示可结晶之意)碎片。最近的研究说明家兔和人的IgG几乎可被所有的蛋白水解酶所分解,所试过的蛋白水酶如木瓜酶、胃酶、胰酶、胰凝乳朊酶及组织朊酶等对IgG     

红藻凝集素G研究进展

来源于海洋红藻的凝集素G已被证实对多种囊膜病毒都有抗病毒活性,可与囊膜病毒表面糖基结合而阻断病毒的入侵。以病毒入侵为作用靶点的抗病毒药物,不仅可以阻断病毒的自由传播途径,还可以阻断细胞间传播途径,红藻凝集素G还具有可溶性好、易表达、稳定性强、免疫原性低、安全性好等优点,所以红藻凝集素G作为一类新型抗病毒药物越来越受到科学家的青睐。     

植物中的G蛋白

G蛋白是一类参与跨膜信号传导的GTP(三磷酸乌苷)结合蛋白质。GTP结合蛋白质是具有重要功能的蛋白质。G蛋白参与的信号传导链可概括为:信号→受体→G蛋白→效应体(靶子)等。70年代末期,在动物腺苷酸环化酶的激素调节研究、视觉光信号传导的研究中发现了G蛋白。动物体内有多种不同功     

G��i and G�¦� Jointly Regulate the Conformations of a G�¦� Effector, the Neuronal G Protein-activated K+ Channel (GIRK)

Stable complexes among G proteins and effectors are an emerging concept in cell signaling. The prototypical Gβγ effector G protein-activated K⁺ channel (GIRK; Kir3) physically interacts with Gβγ but also with Gα_i/o. Whether and how Gα_i/o subunits regulate GIRK in vivo is unclear. We studied triple interactions among GIRK subunits 1 and 2, Gα_i3 and Gβγ. We used in vitro protein interaction assays and in vivo intramolecular Förster resonance energy transfer (i-FRET) between fluorophores attached to N and C termini of either GIRK1 or GIRK2 subunit. We demonstrate, for the first time, that Gβγ and Gα_i3 distinctly and interdependently alter the conformational states of the heterotetrameric GIRK1/2 channel. Biochemical experiments show that Gβγ greatly enhances the binding of GIRK1 subunit to Gα_i3^GDP and, unexpectedly, to Gα_i3^GTP. i-FRET showed that both Gα_i3 and Gβγ induced distinct conformational changes in GIRK1 and GIRK2. Moreover, GIRK1 and GIRK2 subunits assumed unique, distinct conformations when coexpressed with a “constitutively active” Gα_i3 mutant and Gβγ together. These conformations differ from those assumed by GIRK1 or GIRK2 after separate coexpression of either Gα_i3 or Gβγ. Both biochemical and i-FRET data suggest that GIRK acts as the nucleator of the GIRK-Gα-Gβγ signaling complex and mediates allosteric interactions between Gα_i^GTP and Gβγ. Our findings imply that Gα_i/o and the Gα_iβγ heterotrimer can regulate a Gβγ effector both before and after activation by neurotransmitters.     

Gγ1+Gγ2+Gγ3=Gβ: the search for heterotrimeric G-protein γ subunits in Arabidopsis is over

In Arabidopsis, heterotrimeric G-proteins consist of one Gα (GPA1), one Gβ (AGB1) and three Gγ (AGG1, AGG2 and AGG3) subunits. Gβ and Gγ subunits function as obligate heterodimers, therefore any phenotypes observed in Gβ-deficient mutants should be apparent in Gγ-deficient mutants. Nevertheless, the first two Gγ subunits discovered failed to explain many of the phenotypes shown by the agb1 mutants in Arabidopsis, prompting the search for additional Gγ subunits. The recent discovery of an additional, although quite atypical, Gγ subunit in Arabidopsis (AGG3) has helped to complete the picture and explains almost all of the missing agb1 'orphan' phenotypes. There is nevertheless still one unexplained phenotype, the reduction in rosette size reported for agb1, that has not been observed in any of the individual agg mutants or the double agg1agg2 mutant. We have now created a triple gamma mutant (agg1agg2agg3) in Arabidopsis and show that it recapitulates the remaining 'orphan'agb1 phenotypes. Triple agg1agg2agg3 mutants show the reduction in rosette size previously observed in agb1 mutants. In addition we show that small differences in flower and silique size observed between agb1 and agg3 mutants are also accounted for by the triple agg1agg2agg3 mutant. Our results strongly suggest that there are no additional members of the G-protein family remaining to be discovered in Arabidopsis.     

Three new G6PD variants,G6PD Adana,G6PD Samandağ, and G6PD Balcali in Çukurova,Turkey

Summary Glucose-6-phosphate dehydrogenase (G6PD) enzyme from cases known to be completely or mildly deficient were analyzed. The enzymes were purified from blood samples by utilizing DEAE-52 cellulose pH 7.0 column chromatography and ammonium sulphate precipitation. Biochemical and electrophoretic properties of G6PD were studied in these partially purified enzymes. In this study wer report three new variants from Çukurova, named Adana, Samanda, and Balcali. Variant I (G6PD Adana) had a high K_m for G6P (210 M) and NADP (13M). Utilization of 2d-G6P was 38%. It had a slow electrophoretic mobility, a biphasic pH optimum curve, and abnormal heat stability. Variant II (G6PD Samanda) had a low K_m for G6P (25M) and a high K_m for NADP (18M). The rate of utilization of 2d-G6P was normal. G6PD Samanda deviated from the normal enzyme by its biphasic pH optimum curve and its slow electrophoretic mobility. Variant III (G6PD-Balcali) had a normal K_m G6P, NADP and rate of utilization of 2d-G6P. However, it showed a biphasic pH optimum curve and slow electrophoretic mobility.     

小麦萌发素G和ψG的纯化及其部分特性

利用亲和层析方法纯化了小麦草酸氧化酶G和ψG,并对其生化特性进行了初步分析.G和ψG的最适pH为3.5,在60℃以下较稳定.当草酸浓度大于0.2mmol/L时,G和ψG的活性受到抑制.G和ψG的Km值分别为0.084和0.053mmol/L.0.1 mmol/L的EDTA、NH4 、Cl-、Mn2 、Mg2 、Na 和K 对G和ψG的活性没有影响,0.1 mmol/L的Zn2 、Cu2 、Fez 、Al3 、CO32-、NO3-和SO42-抑制G和ψG的活性.0.1 mmol/L的H2PO4-和HPO42-仅抑制G的活性.0.1 mmol/L的核黄素、FMN和FAD抑制ψG活性,G的活性则不受FAD和FMN的影响.     

G－蛋白异三聚体（G－proteinheterotrimer）的晶体结构

继１９９４年Ｓｉｇｌｅｒ－ｈａｍｍ和Ｓｐｒａｎｇ－Ｇｉｌｍａｎ实验室报道了Ｇｉα１的晶体结构之后,１９９５年１２月和１９９６年１月这两个实验室又相继报道了Ｇ－蛋白异三聚体（ＧαＧＤＰ）βγ和Ｇβγ二聚体的晶体结构．这些研究结果表明Ｇ－蛋白复合物象一台由操纵杆（受体）、开关（Ｇα）和螺旋桨（Ｇβγ）组成的信号转导纳米机器,并揭示了α和β亚基间可能存在两种不同的功能界面,β和γ亚基间、α和γ的相互作用,以及信号传导过程中,ＧＴＰ诱导开关Ⅱ区重排和亚基解高的机制．βγ亚基能稳定α亚基和ＧＤＰ的紧密结合,使Ｇ－蛋白维持在失活状态．β亚基的ＷＤ４０重复序列形成７叶片的螺旋桨（ｓｅｖｅｎｆｏｌｄｐｒｏｐｅｌｌｅｒ）构造,每个叶片的外侧面显露出许多可变的接触位点．β亚基部分地为伸展的γ亚基包围。关键词