G蛋白偶联受体研究进展

G蛋白偶联受体(Gprotein-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家族。按GPCRs一级结构的同源性,主要分为A、B、C三族;按氨基酸序列的相似性以及与配基的结合情况GPCRs可以分为5个亚家族。本文就GPCRs的结构、分类、GPCRs的二聚化以及其固有活性等方面做了一些介绍。     

GPCR高度保守位点与二聚化功能

G蛋白偶联受体(G protein-coupled receptors,GPCRs)是具有7个跨膜螺旋的蛋白受体,根据其序列的相似性以及与配基的结合情况,共分为五个亚家族,是人体内最大的蛋白质家族,也是重要的药物靶标.它的结构与功能的研究对于新药的开发、研制以及推动医药领域的发展起着举足轻重的作用.     

GPR50生物学功能研究进展

G蛋白偶联受体50(G protein-coupled receptor, GPR50)是属于G蛋白偶联受体(G protein-coupled receptors, GPCRs)超级家族的一类跨膜蛋白,与Mel1c受体同源,介导跨膜转运和信号传递,在神经系统发育、能量代谢调节及糖皮质激素受体信号等多种生理活动中发挥重要作用,同时也是阿尔茨海默病、肝癌等疾病的潜在生物学标志物,阐明GPR50的生理功能有助于为相关疾病治疗的进展、预后和发展提供可能方向.近年来,随着GPR50潜在作用不断被发现,其涉及的生理功能也不断被拓宽.详细介绍了GPR50的分子结构特征,总结了近年来GPR50的生物学功能研究进展,为GPR50的进一步研究提供参考.     

揭开细胞信号传导之谜——解读2012年诺贝尔化学奖

<正>罗伯特·莱夫科维茨10月10日,因为对"G蛋白偶联受体"的研究,两位美国科学家——杜克大学医学中心教授、69岁的罗伯特·莱夫科维茨(Robert Lefkowitz)和斯坦福大学医学院教授、57岁的布莱恩·科比尔卡(Brian Kobilka)分享了今年的诺贝尔化学奖。他们破解了人体信息交流系统的秘密,即身体如何感知外部世界,并将信息发送到细胞。该项研究成果将有助于新药物的开发。而18年前,G蛋白和G蛋白偶联受体(GPCRs)就曾令他们的发现者——两名美国科学家获得了诺贝尔生理学或医学奖。     

抗炎药物CCR2拮抗剂的研究进展

CCR2属于G蛋白偶联受体超家族成员,并且是MCP1-4的受体,而MCP1-4是促炎症反应的化学诱导物。CCR2是炎症单核细胞最早的化学催化受体,在T-细胞、树状突细胞和上皮细胞都有表达,通过与配体衔接,CCR2介导炎症细胞移动和激活。     

解析蛋白质结构,助力新药研发 以艾滋病、心脏病、糖尿病等重要疾病为目标

<正>G蛋白偶联受体(GPCR)是人体内最大的受体蛋白家族,在细胞的信号传导中发挥着关键作用,与多种疾病息息相关。很多药物正是通过与G蛋白偶联受体相互作用而发挥功能的。在短短的6年时间里,中国科学院上海药物研究所吴蓓丽研究员与团队成员成功解析了8种与传染性疾病、心血管疾病、代谢性疾病相关的G蛋白偶联受体的结构,发现了多个药物结合位点,推动了新药的研发,并因此获得了陈嘉庚青年科学奖。     

植物小G蛋白研究进展

小G蛋白是和异三聚体G蛋白α亚基偶联的单体鸟苷酸结合蛋白,所有的小G蛋白从属于Ras超家族．植物小G蛋白超家族尤其是ROP家族在信号转导及生长发育中起了重要的“分子开关”作用,它们参与调控花粉管的伸长、根毛的发育及激素信号转导等过程．主要介绍了小G蛋白的种类、调节机制、ROP家族的功能及靶物,旨在揭示植物小G蛋白功能的多样性．     

前列腺素E_2受体EP_3及其调节剂的研究进展

前列腺素受体类型繁多,可以偶联G蛋白介导多种生理病理过程.其中前列腺素E2受体有4种亚型:EP1、EP2、EP3和EP4.EP3受体由于其亚型多样性及偶联G蛋白的复杂性使其成为众多前列腺素E2受体中较特殊的"成员".EP3的抗凝血功能研究及新型调节剂的研发是目前该领域研究的热点.本文主要阐述EP3的分布、主要功能及其调节剂的研究进展.     

杭炎药物CCR2拮抗剂的研究进展

CCR2属于G蛋白偶联受体超家族成员,并且是MCP1-4的受体,而MCPI-4是促炎症反应的化学诱导物.CCR2是炎症单核细胞最早的化学催化受体,在T-细胞、树状突细胞和上皮细胞都有表达,通过与配体衔接,CCR2介导炎症细胞移动和激活.CCR2最早的配体MCP-1在人类很多炎症中都会增加,MCP-1和CCR2在人类侵蚀性疾病模型如动脉粥状硬化及多发性硬化症中都起到明显作用.     

百日咳毒素与霍乱毒素对乙酰酰胆碱诱导气孔运动的影响

在动物细胞中神经递质乙酰胆碱与其受体结合后，通过G蛋白的偶联传递信号。在植物中，乙酰胆碱也普遍存在并参与调节许多生理过程。乙酰胆碱及其受体参与了气孔运动的调节，G蛋白的激活剂霍乱毒素与抑制剂百日咳毒素影响乙酰胆碱诱导的气孔开放，而且仅在含Ca^2 的介质中才能起作用；同时用Ca^2 荧光探针Fluo-3检测保卫细胞胞质Ca^2 动态变化，表明乙酰胆碱的胞内信号转导中有Ca^2 的参与。由此推测在毒蕈碱型乙酰胆碱受体介导乙酰胆碱诱导的气孔运动中，可能存在与G蛋白偶联的信号转导。     

Molecular characterization of the melanin-concentrating-hormone receptor.

Orphan G-protein-coupled receptors (GPCRs) are cloned proteins with structural characteristics common to the GPCRs but that bind unidentified ligands. Orphan GPCRs have been used as targets to identify novel transmitter molecules. Here we describe the isolation from brain extracts and the characterization of the natural ligand of a particular orphan GPCR (SLC-1) that is sequentially homologous to the somatostatin receptors. We show that the natural ligand of this receptor is the neuropeptide melanin-concentrating hormone (MCH). MCH is a cyclic peptide that regulates a variety of functions in the mammalian brain, in particular feeding behaviour. We demonstrate that nanomolar concentrations of MCH strongly activate SLC-1-related pathways through G(alpha)i and/or G(alpha)q proteins. We have analysed the tissue localization of the MCH receptor and find that it is expressed in several brain regions, in particular those involved in olfactory learning and reinforcement mechanisms, indicating that therapies targeting the MCH receptor should act on the neuronal regulation of food consumption.     

Movement of 'gating charge' is coupled to ligand binding in a G-protein-coupled receptor

Activation by agonist binding of G-protein-coupled receptors (GPCRs) controls most signal transduction processes. Although these receptors span the cell membrane, they are not considered to be voltage sensitive. Recently it was shown that both the activity of GPCRs and their affinity towards agonists are regulated by membrane potential. However, it remains unclear whether GPCRs intrinsically respond to changes in membrane potential. Here we show that two prototypical GPCRs, the m2 and m1 muscarinic receptors (m2R and m1R), display charge-movement-associated currents analogous to 'gating currents' of voltage-gated channels. The gating charge-voltage relationship of m2R correlates well with the voltage dependence of the affinity of the receptor for acetylcholine. The loop that couples m2R and m1R to their G protein has a crucial function in coupling voltage sensing to agonist-binding affinity. Our data strongly indicate that GPCRs serve as sensors for both transmembrane potential and external chemical signals.     

Structure and function of an irreversible agonist-β(2) adrenoceptor complex

G-protein-coupled receptors (GPCRs) are eukaryotic integral membrane proteins that modulate biological function by initiating cellular signalling in response to chemically diverse agonists. Despite recent progress in the structural biology of GPCRs, the molecular basis for agonist binding and allosteric modulation of these proteins is poorly understood. Structural knowledge of agonist-bound states is essential for deciphering the mechanism of receptor activation, and for structure-guided design and optimization of ligands. However, the crystallization of agonist-bound GPCRs has been hampered by modest affinities and rapid off-rates of available agonists. Using the inactive structure of the human β(2) adrenergic receptor (β(2)AR) as a guide, we designed a β(2)AR agonist that can be covalently tethered to a specific site on the receptor through a disulphide bond. The covalent β(2)AR-agonist complex forms efficiently, and is capable of activating a heterotrimeric G protein. We crystallized a covalent agonist-bound β(2)AR-T4L fusion protein in lipid bilayers through the use of the lipidic mesophase method, and determined its structure at 3.5?? resolution. A comparison to the inactive structure and an antibody-stabilized active structure (companion paper) shows how binding events at both the extracellular and intracellular surfaces are required to stabilize an active conformation of the receptor. The structures are in agreement with long-timescale (up to 30?μs) molecular dynamics simulations showing that an agonist-bound active conformation spontaneously relaxes to an inactive-like conformation in the absence of a G protein or stabilizing antibody.     

Structure of a nanobody-stabilized active state of the β(2) adrenoceptor

G protein coupled receptors (GPCRs) exhibit a spectrum of functional behaviours in response to natural and synthetic ligands. Recent crystal structures provide insights into inactive states of several GPCRs. Efforts to obtain an agonist-bound active-state GPCR structure have proven difficult due to the inherent instability of this state in the absence of a G protein. We generated a camelid antibody fragment (nanobody) to the human β(2) adrenergic receptor (β(2)AR) that exhibits G protein-like behaviour, and obtained an agonist-bound, active-state crystal structure of the receptor-nanobody complex. Comparison with the inactive β(2)AR structure reveals subtle changes in the binding pocket; however, these small changes are associated with an 11?? outward movement of the cytoplasmic end of transmembrane segment 6, and rearrangements of transmembrane segments 5 and 7 that are remarkably similar to those observed in opsin, an active form of rhodopsin. This structure provides insights into the process of agonist binding and activation.     

G-protein-coupled receptor heterodimerization modulates receptor function.

The opioid system modulates several physiological processes, including analgesia, the stress response, the immune response and neuroendocrine function. Pharmacological and molecular cloning studies have identified three opioid-receptor types, delta, kappa and mu, that mediate these diverse effects. Little is known about the ability of the receptors to interact to form new functional structures, the simplest of which would be a dimer. Structural and biochemical studies show that other G-protein-coupled receptors (GPCRs) interact to form homodimers. Moreover, two non-functional receptors heterodimerize to form a functional receptor, suggesting that dimerization is crucial for receptor function. However, heterodimerization between two fully functional receptors has not been documented. Here we provide biochemical and pharmacological evidence for the heterodimerization of two fully functional opioid receptors, kappa and delta. This results in a new receptor that exhibits ligand binding and functional properties that are distinct from those of either receptor. Furthermore, the kappa-delta heterodimer synergistically binds highly selective agonists and potentiates signal transduction. Thus, heterodimerization of these GPCRs represents a novel mechanism that modulates their function.     

Structure of the δ-opioid receptor bound to naltrindole

The opioid receptor family comprises three members, the μ-, δ- and κ-opioid receptors, which respond to classical opioid alkaloids such as morphine and heroin as well as to endogenous peptide ligands like endorphins. They belong to the G-protein-coupled receptor (GPCR) superfamily, and are excellent therapeutic targets for pain control. The δ-opioid receptor (δ-OR) has a role in analgesia, as well as in other neurological functions that remain poorly understood. The structures of the μ-OR and κ-OR have recently been solved. Here we report the crystal structure of the mouse δ-OR, bound to the subtype-selective antagonist naltrindole. Together with the structures of the μ-OR and κ-OR, the δ-OR structure provides insights into conserved elements of opioid ligand recognition while also revealing structural features associated with ligand-subtype selectivity. The binding pocket of opioid receptors can be divided into two distinct regions. Whereas the lower part of this pocket is highly conserved among opioid receptors, the upper part contains divergent residues that confer subtype selectivity. This provides a structural explanation and validation for the 'message-address' model of opioid receptor pharmacology, in which distinct 'message' (efficacy) and 'address' (selectivity) determinants are contained within a single ligand. Comparison of the address region of the δ-OR with other GPCRs reveals that this structural organization may be a more general phenomenon, extending to other GPCR families as well.     

The structural basis of agonist-induced activation in constitutively active rhodopsin

G-protein-coupled receptors (GPCRs) comprise the largest family of membrane proteins in the human genome and mediate cellular responses to an extensive array of hormones, neurotransmitters and sensory stimuli. Although some crystal structures have been determined for GPCRs, most are for modified forms, showing little basal activity, and are bound to inverse agonists or antagonists. Consequently, these structures correspond to receptors in their inactive states. The visual pigment rhodopsin is the only GPCR for which structures exist that are thought to be in the active state. However, these structures are for the apoprotein, or opsin, form that does not contain the agonist all-trans retinal. Here we present a crystal structure at a resolution of 3 ? for the constitutively active rhodopsin mutant Glu 113 Gln in complex with a peptide derived from the carboxy terminus of the α-subunit of the G protein transducin. The protein is in an active conformation that retains retinal in the binding pocket after photoactivation. Comparison with the structure of ground-state rhodopsin suggests how translocation of the retinal β-ionone ring leads to a rotation of transmembrane helix 6, which is the critical conformational change on activation. A key feature of this conformational change is a reorganization of water-mediated hydrogen-bond networks between the retinal-binding pocket and three of the most conserved GPCR sequence motifs. We thus show how an agonist ligand can activate its GPCR.     

Structure and dynamics of the M3 muscarinic acetylcholine receptor

Acetylcholine, the first neurotransmitter to be identified, exerts many of its physiological actions via activation of a family of G-protein-coupled receptors (GPCRs) known as muscarinic acetylcholine receptors (mAChRs). Although the five mAChR subtypes (M1-M5) share a high degree of sequence homology, they show pronounced differences in G-protein coupling preference and the physiological responses they mediate. Unfortunately, despite decades of effort, no therapeutic agents endowed with clear mAChR subtype selectivity have been developed to exploit these differences. We describe here the structure of the G(q/11)-coupled M3 mAChR ('M3 receptor', from rat) bound to the bronchodilator drug tiotropium and identify the binding mode for this clinically important drug. This structure, together with that of the G(i/o)-coupled M2 receptor, offers possibilities for the design of mAChR subtype-selective ligands. Importantly, the M3 receptor structure allows a structural comparison between two members of a mammalian GPCR subfamily displaying different G-protein coupling selectivities. Furthermore, molecular dynamics simulations suggest that tiotropium binds transiently to an allosteric site en route to the binding pocket of both receptors. These simulations offer a structural view of an allosteric binding mode for an orthosteric GPCR ligand and provide additional opportunities for the design of ligands with different affinities or binding kinetics for different mAChR subtypes. Our findings not only offer insights into the structure and function of one of the most important GPCR families, but may also facilitate the design of improved therapeutics targeting these critical receptors.