C 族GPCRs 寡聚体的激活机制

C族GPCRs是体内重要的受体亚家族,参与众多重要的生理和病理进程。该族受体的单体包含七螺旋跨膜结构(heptahelical transmembrane domain,HD)、捕蝇草模块(venus flytrap domain,VFT)和半胱氨酸富集区(cysteine-rich domain,CRD)、C末端等多个功能域,同时形成组成性的二聚体和寡聚体。这种多功能域寡聚体结构使该家族受体的激活机制非常复杂,本文回顾和介绍了多年以来对该家族受体在单体、二聚体、寡聚体等多个层面的激活机制研究的历程和进展,同时也展望了进一步的研究方向和这些研究成果对于开发新型药物的意义。     

C族G蛋白偶联受体激活过程

C族G蛋白偶联受体(G protein coupled receptor,GPCR)具有七螺旋跨膜域(heptahelical transmembranedomain,HD)、捕蝇夹域(venusflytrapdomain,VFT)和半胱氨酸富集域(cysteine-rich domain,CRD)等功能域,并在体内组成性形成二聚体。该文介绍C族G蛋白偶联受体激活进程中各功能域的构象变化,以及由此产生的构象学效应。     

GPCRs 组成性活性的研究进展及意义

GPCRs是体内最大的蛋白质亚家族,其活性涉及体内绝大部分重要的生理和病理进程。研究表明,GPCRs或其突变体能在无配体结合的情况下自发产生部分甚至完全活性程度的生理活性,称之为组成性活性。据此研究者提出了GPCRs激活过程中存在多个中间激活态的观点,从而丰富了配体受体相互作用的经典模型,并使组成性活性突变体(constitutive active mutant,CAM)成为研究GPCRs的新方法。本文系统介绍了组成性活性的研究历程,以及近年来利用CAM的方法研究GPCRs的结构、激活机制和活性调节的历程和进展,和体内组成性活性突变的成因和与疾病的关系,以及CAM在研究药物作用机理和新药研发中的意义。     

G蛋白偶联受体的研究进展

G蛋白偶联受体（GPCRs）,是体内最大的蛋白质超家族。GPCRs的基本结构巳清楚,但高分辨率的三维结构还未得到。根据结构的同源性,GPCRs主要分为A、B、C3族。GPCRs配体的多样性决定配体结合域的多样性。受体分子内相互作用力的破坏,质子化,构象变化,与G蛋白的偶联以及受体二聚化参与了GPCRs的活化过程。GPCRs的活化模式有3种;二态模式、多态模式和顺序结合的构象选择模式。     

G蛋白偶联受体转激活酪氨酸激酶受体机制

G蛋白偶联受体(G-protien coupled receptors,GPCRs)和酪氨酸激酶受体(receptor tyrosine kinases,RTKs)是体内两类重要的受体家族,介导着绝大多数信号事件。GPCRs能够"绑架"RTKs进行信号转导,即GPCRs能够在没有外加RTKs配体的情况下激活RTKs,这种现象称为转激活。作为转激活的核心过程,GPCR调控RTK磷酸化主要采取RTK配体依赖模式和非RTK配体依赖模式。不同的G蛋白亚型、酪氨酸磷酸激酶、酪氨酸磷酸酶(protein-tyrosine phosphatases,PTPs)以及活性氧自由基(reactiveoxygen species,ROS)均在此过程中具有重要作用。GPCR和RTK还能形成信号复合体(signaling complex)从而实现蛋白质之间的动态相互作用。对转激活的研究为GPCR靶点药物开发提供了新思路。     

植物G蛋白偶联受体及其在信号转导中的作用

G蛋白偶联受体(G protein-coupled receptors,GPCRs)是具有7个跨膜螺旋的蛋白质受体,是人体内最大的蛋白质超家族.GPCRs能调控细胞周期,参与多种植物信号通路以及影响一系列的代谢和分化活动.简要介绍了GPCR和G蛋白介导的信号转导机制,GPCRs的结构和植物GPCR及其在植物跨膜信号转导中的作用,并对GPCR的信号转导机制及植物抗病反应分子机制的研究提出展望.     

G蛋白偶联受体相关分选蛋白功能特征与相关疾病研究进展

G蛋白偶联受体(G protein-coupled receptors, GPCRs)作为最大的一类膜蛋白受体家族,可被多种配体激活并发挥相应的信号转导功能,参与生物体内重要的生理过程。G蛋白偶联受体相关分选蛋白(G protein-coupled receptors associated sorting proteins, GASPs)则对内吞后的GPCRs分选过程发挥着重要的作用,并介导受体进入降解或再循环途径,进而调控细胞的信号转导等过程。研究发现GASPs的功能缺陷与多种疾病相关,包括神经系统疾病、肿瘤和耳聋等。本文重点介绍了G蛋白偶联受体相关分选蛋白的功能特征及其相关信号通路,描述了GASPs功能缺陷与疾病的关联性及家族蛋白与GPCRs的相互作用、GASPs分选途径的发现、参与的信号通路及对基因转录调控,以期为GASPs相关多种疾病的治疗提供新的思路和策略。     

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。     

哺乳类C型凝集素超级家族

C型凝集素超级家族根据其糖识别域(CRD)的一级结构分为蛋白聚糖、Ⅱ型跨膜受体、胶原凝素、选凝素、自然杀伤细胞受体及多CRDⅠ型跨膜受体等6个家族. 每一家族的成员具有同源的氨基酸序列、相同的总体分子结构及类似的生物学功能.从CRD的一级结构至三级结构水平确定了C型凝集素选择性糖识别的分子基础.     

棕榈酰化修饰对G蛋白偶联受体功能的调节作用

G蛋白偶联受体(G-protein-coupled receptors,GPCRs)作为跨膜蛋白,其结构和功能同时受相互作用的蛋白质和脂质分子调控.S-棕榈酰化(S-palmitoylation)能够影响GPCRs与信号蛋白及膜脂分子的相互作用,在GPCRs相关的多项生理进程中发挥重要调节作用.棕榈酸与GPCRs的半胱氨酸间形成不稳定的硫酯键,其修饰动力学过程受棕榈酰转移酶(protein acly transferases,PATs)与硫酯酶(thioesterases)之间的可逆性双重调控,与受体活性及生理状态密切相关.棕榈酰化修饰多发生在GPCRs的C末端,通过棕榈酸侧链插入到质膜内侧而形成第4和/或第5个胞内环,从而影响GPCRs的构象,促进其正确折叠与成熟,并对GPCRs胞内转运、分选、下游信号转导、失敏、内化、寡聚化等活动产生影响.此外,棕榈酰化还与磷酸化、泛素化及亚硝基化等多种翻译后修饰机制相互作用,共同参与调节GPCRs的功能.GPCRs的棕榈酰化修饰酶学机制以及GPCRs蛋白复合体棕榈酰化修饰胞内动力学过程将是未来的研究热点.     

Coupling of agonist binding to effector domain activation in metabotropic glutamate-like receptors

Many membrane receptors are made of a ligand binding domain and an effector domain mediating intracellular signaling. This is the case for the metabotropic glutamate-like G-protein-coupled receptors. How ligand binding leads to the active conformation of the effector domain in such receptors is largely unknown. Here, we used an evolutionary trace analysis and mutagenesis to identify critical residues involved in the allosteric coupling between the Venus flytrap ligand binding domain (VFT) and the heptahelical G-protein activating domain of the metabotropic glutamate-like receptors. We have shown that a conserved interdomain disulfide bridge is required for this allosteric interaction. Taking into account that these receptors are homodimers, this finding provides important new information explaining how the different conformations of the dimer of VFT lead to different signaling of such dimeric receptors.     

A dimerization hierarchy in the transmembrane domains of the HER receptor family

Bitopic membrane proteins offer an opportunity for studying transmembrane domain interactions without the structural complexity inherent to multitopic integral membrane proteins. To date, only homomeric associations have been extensively studied quantitatively. Here we propose to assess the thermodynamics of heteromeric associations, which opens the way to investigating specificity and selectivity. A very interesting system of biological relevance with single transmembrane domains possibly involved in interactions with different partners is the EGFR receptor family. The four members, all tyrosine kinase receptors, are involved in an interaction network that potentially leads to a complete set of homo- and heterodimers, ideally suited to such a study. Furthermore, the transmembrane domains of these receptors have been previously implicated in their function in the past by mutations in the transmembrane domain leading to constitutive activation. We demonstrate, using a fluorescence-based measurement of interaction energies, a hierarchy of transmembrane domain interactions ranging from a noninteractive pair to strong dimerization. We propose a structural model based on the crystal structure of the EGFR dimer, to show how the dimeric structure favors these interactions. The correlation we observe between transmembrane domain and whole receptor interaction hierarchies opens a new perspective, suggesting a role for transmembrane receptor domains in the modulation of receptor signaling.     

Membrane topology of a metabotropic glutamate receptor

The metabotropic glutamate receptors (mGluRs) have been predicted to have a classical seven transmembrane domain structure similar to that seen for members of the G-protein-coupled receptor (GPCR) superfamily. However, the mGluRs (and other members of the family C GPCRs) show no sequence homology to the rhodopsin-like GPCRs, for which this seven transmembrane domain structure has been experimentally confirmed. Furthermore, several transmembrane domain prediction algorithms suggest that the mGluRs have a topology that is distinct from these receptors. In the present study, we set out to test whether mGluR5 has seven true transmembrane domains. Using a variety of approaches in both prokaryotic and eukaryotic systems, our data provide strong support for the proposed seven transmembrane domain model of mGluR5. We propose that this membrane topology can be extended to all members of the family C GPCRs.     

Activation of a dimeric metabotropic glutamate receptor by intersubunit rearrangement

Although many G protein-coupled receptors (GPCRs) can form dimers, a possible role of this phenomenon in their activation remains elusive. A recent and exciting proposal is that a dynamic intersubunit interplay may contribute to GPCR activation. Here, we examined this possibility using dimeric metabotropic glutamate receptors (mGluRs). We first developed a system to perfectly control their subunit composition and show that mGluR dimers do not form larger oligomers. We then examined an mGluR dimer containing one subunit in which the extracellular agonist-binding domain was uncoupled from the G protein-activating transmembrane domain. Despite this uncoupling in one protomer, agonist stimulation resulted in symmetric activation of either transmembrane domain in the dimer with the same efficiency. This, plus other data, can only be explained by an intersubunit rearrangement as the activation mechanism. Although well established for other types of receptors such as tyrosine kinase and guanylate cyclase receptors, this is the first clear demonstration that such a mechanism may also apply to GPCRs.     

How do G-protein-coupled receptors work? The case of metabotropic glutamate and GABA receptors

G-protein coupled receptors (GPCRs) represent the largest membrane proteins family in animal genomes. Being the receptors for most hormones and neurotransmitters, these proteins play a central role in intercellular communication. GPCRs can be classified into several groups based on the sequence similarity of their common structural feature: the heptahelical domain. The metabotropic receptors for the main neurotransmitters glutamate and gamma-aminobutyric acid (GABA) belong to the class III of GPCRs, together with others receptors for Ca2+, for sweet and amino acid taste compounds and for some pheromones, as well as for odorants in fish. Besides their transmembrane heptahelical domain responsible for G-protein activation, most of class III receptors possess a large extracellular domain responsible for ligand recognition. The recent resolution of the structure of this binding domain of one of these receptors, the mGlu1 receptor, together with the recent demonstration that these receptors are dimers, revealed an original mechanism of activation for these GPCRs. Such data open new possibilities to develop drugs aimed at modulating these receptors, and raised a number of interesting questions on the activation mechanism of other GPCRs.     

Structural requirements for mutational lutropin/choriogonadotropin receptor activation

Different activation mechanisms of glycoprotein hormone receptors, which are members of the G protein-coupled receptor superfamily, have been proposed. For example, the large ectodomain of glycoprotein hormone receptors may function as an inverse agonist keeping the transmembrane domain in an inactive conformation. To provide support for this hypothesis, we have generated different lutropin/choriogonadotropin receptor (LHR) constructs lacking the ectodomain. Although some ectodomain-deficient LHR constructs were targeted to the cell surface, cAMP levels remained unchanged under basal conditions and agonist application but could be increased by a mutation within the transmembrane domain 6 (D578H). Taking advantage of a constitutive activating mutation (S277N) located in the extracellular domain, we showed that the intact leucine-rich repeat-containing ectodomain is essential for constitutive activation of the LHR by mutation of the hinge region. Our findings support an activation scenario in which agonist binding or mutational alterations expose a structure within the ectodomain, which then activates the transmembrane core.     

Comparison of class A and D G protein-coupled receptors: common features in structure and activation

All G protein-coupled receptors (GPCRs) share a common seven TM helix architecture and the ability to activate heterotrimeric G proteins. Nevertheless, these receptors have widely divergent sequences with no significant homology. We present a detailed structure-function comparison of the very divergent Class A and D receptors to address whether there is a common activation mechanism across the GPCR superfamily. The Class A and D receptors are represented by the vertebrate visual pigment rhodopsin and the yeast alpha-factor pheromone receptor Ste2, respectively. Conserved amino acids within each specific receptor class and amino acids where mutation alters receptor function were located in the structures of rhodopsin and Ste2 to assess whether there are functionally equivalent positions or regions within these receptors. We find several general similarities that are quite striking. First, strongly polar amino acids mediate helix interactions. Their mutation generally leads to loss of function or constitutive activity. Second, small and weakly polar amino acids facilitate tight helix packing. Third, proline is essential at similar positions in transmembrane helices 6 and 7 of both receptors. Mapping the specific location of the conserved amino acids and sites of constitutively active mutations identified conserved microdomains on transmembrane helices H3, H6, and H7, suggesting that there are underlying similarities in the mechanism of the widely divergent Class A and Class D receptors.