scholarly journals Structural basis of GABAB receptor–Gi protein coupling

Nature ◽  
2021 ◽  
Author(s):  
Cangsong Shen ◽  
Chunyou Mao ◽  
Chanjuan Xu ◽  
Nan Jin ◽  
Huibing Zhang ◽  
...  
Keyword(s):  
G Protein ◽  
Transmembrane Domain ◽  
Gabab Receptor ◽  
Transmembrane Helix ◽  
Active Form ◽  
Binding Mode ◽  
Structural Basis ◽  
Intracellular Loop ◽  
Protein Activation ◽  
Gi Protein

AbstractG-protein-coupled receptors (GPCRs) have central roles in intercellular communication1,2. Structural studies have revealed how GPCRs can activate G proteins. However, whether this mechanism is conserved among all classes of GPCR remains unknown. Here we report the structure of the class-C heterodimeric GABAB receptor, which is activated by the inhibitory transmitter GABA, in its active form complexed with Gi1 protein. We found that a single G protein interacts with the GB2 subunit of the GABAB receptor at a site that mainly involves intracellular loop 2 on the side of the transmembrane domain. This is in contrast to the G protein binding in a central cavity, as has been observed with other classes of GPCR. This binding mode results from the active form of the transmembrane domain of this GABAB receptor being different from that of other GPCRs, as it shows no outside movement of transmembrane helix 6. Our work also provides details of the inter- and intra-subunit changes that link agonist binding to G-protein activation in this heterodimeric complex.

scholarly journals Structure and dynamics of the active human parathyroid hormone receptor-1

Science ◽  
2019 ◽  
Vol 364 (6436) ◽  
pp. 148-153 ◽  
Author(s):  
Li-Hua Zhao ◽  
Shanshan Ma ◽  
Ieva Sutkeviciute ◽  
Dan-Dan Shen ◽  
X. Edward Zhou ◽  
...  
Keyword(s):  
Parathyroid Hormone ◽  
G Protein ◽  
Hormone Receptor ◽  
Transmembrane Domain ◽  
Transmembrane Helix ◽  
Receptor Activation ◽  
Structural Basis ◽  
Parathyroid Hormone Receptor ◽  
Class B ◽  
Long Acting

The parathyroid hormone receptor-1 (PTH1R) is a class B G protein–coupled receptor central to calcium homeostasis and a therapeutic target for osteoporosis and hypoparathyroidism. Here we report the cryo–electron microscopy structure of human PTH1R bound to a long-acting PTH analog and the stimulatory G protein. The bound peptide adopts an extended helix with its amino terminus inserted deeply into the receptor transmembrane domain (TMD), which leads to partial unwinding of the carboxyl terminus of transmembrane helix 6 and induces a sharp kink at the middle of this helix to allow the receptor to couple with G protein. In contrast to a single TMD structure state, the extracellular domain adopts multiple conformations. These results provide insights into the structural basis and dynamics of PTH binding and receptor activation.

scholarly journals Structural Determinants for G Protein Activation and Selectivity in the Second Intracellular Loop of the Thyrotropin Receptor

Endocrinology ◽  
2005 ◽  
Vol 146 (1) ◽  
pp. 477-485 ◽  
Author(s):  
Susanne Neumann ◽  
Gerd Krause ◽  
Maren Claus ◽  
Ralf Paschke
Keyword(s):  
G Protein ◽  
Transmembrane Domain ◽  
Point Mutations ◽  
Hydrophobic Residue ◽  
Intracellular Loop ◽  
Structural Determinants ◽  
Protein Activation ◽  
G Protein Activation ◽  
Potential Interactions ◽  
Receptor Domain

The TSH receptor (TSHR) activates mainly two signal transduction pathways, cAMP production and phosphoinositide turnover, mediated by Gs and Gq coupling, respectively. Several activating deletion and point mutations within intracellular loop 3 (ICL3) and the adjacent portion of transmembrane domain 6 (TM6) support a direct G protein activation by this receptor domain. The ICL3, however, is predicted by modeling to interact with other receptor domains, primarily ICL2, to form a pocket for G protein binding and to allow optimum interaction. Systematic mutagenesis was used to identify important sites within ICL2 and potential interactions between ICL2 and ICL3 of the TSHR required for G protein coupling. Deletions of four or five residues and their corresponding multiple alanine substitutions were introduced into ICL2. Residues I523-D530, comprising mainly the N-terminal half of ICL2, appeared to be critical for Gs- and Gq-mediated signaling. A single alanine substitution screening within ICL2 revealed hydrophobic residue M527 in particular and, to lesser extents, F525, R528, L529, and D530 as residues that selectively abolished or strongly impaired Gq activation. Molecular modeling suggests that F525 interacts with ICL3. To test this hypothesis, ICL2/ICL3 double mutants introducing strong complementary properties were constructed and tested for functional rescue of Gq-mediated signaling. Our results indicate that ICL2 interacts with ICL3 in close vicinity to F525 and T607, suggesting a conformational cooperation between ICL2 and ICL3 during Gq activation by TSHR.

scholarly journals Steroid and G Protein Binding Characteristics of the Seatrout and Human Progestin Membrane Receptor α Subtypes and Their Evolutionary Origins

Endocrinology ◽  
2007 ◽  
Vol 148 (2) ◽  
pp. 705-718 ◽  
Author(s):  
Peter Thomas ◽  
Y. Pang ◽  
J. Dong ◽  
P. Groenen ◽  
J. Kelder ◽  
...  
Keyword(s):  
G Protein ◽  
Hormone Receptors ◽  
G Protein Coupled Receptors ◽  
Spotted Seatrout ◽  
Immunocytochemical Staining ◽  
Intracellular Loop ◽  
Binding Characteristics ◽  
Protein Activation ◽  
Gi Protein ◽  
G Protein Coupled

A novel progestin receptor (mPR) with seven-transmembrane domains was recently discovered in spotted seatrout and homologous genes were identified in other vertebrates. We show that cDNAs for the mPR α subtypes from spotted seatrout (st-mPRα) and humans (hu-mPRα) encode progestin receptors that display many functional characteristics of G protein-coupled receptors. Flow cytometry and immunocytochemical staining of whole MDA-MB-231 cells stably transfected with the mPRαs using antibodies directed against their N-terminal regions show the receptors are localized on the plasma membrane and suggest the N-terminal domain is extracellular. Both recombinant st-mPRα and hu-mPRα display high affinity (Kd 4.2–7.8 nm), limited capacity (Bmax 0.03–0.32 nm), and displaceable membrane binding specific for progestins. Progestins activate a pertussis toxin-sensitive inhibitory G protein (Gi) to down-regulate membrane-bound adenylyl cyclase activity in both st-mPRα- and hu-mPRα-transfected cells. Coimmunoprecipitation experiments demonstrate the receptors are directly coupled to the Gi protein. Similar to G protein-coupled receptors, dissociation of the receptor/G protein complex results in a decrease in ligand binding to the mPRαs and mutation of the C-terminal, and third intracellular loop of st-mPRα causes loss of ligand-dependent G protein activation. Phylogenetic analysis indicates the mPRs are members of a progesterone and adipoQ receptor (PAQR) subfamily that is only present in chordates, whereas other PAQRs also occur in invertebrates and plants. Progesterone and adipoQ receptors are related to the hemolysin3 family and have origins in the Eubacteria. Thus, mPRs arose from Eubacteria independently from members of the GPCR superfamily, which arose from Archeabacteria, suggesting convergent evolution of seven-transmembrane hormone receptors coupled to G proteins.

scholarly journals Structures of metabotropic GABAB receptor

2020 ◽  
Author(s):  
Makaía M. Papasergi-Scott ◽  
Michael J. Robertson ◽  
Alpay B. Seven ◽  
Ouliana Panova ◽  
Jesper M. Mathiesen ◽  
...  
Keyword(s):  
Ligand Binding ◽  
G Protein ◽  
Cellular Response ◽  
Transmembrane Domain ◽  
Gabab Receptor ◽  
Rational Drug Design ◽  
Protein Activation ◽  
Brain Physiology ◽  
Rational Drug ◽  
G Protein Activation

AbstractGABA (γ-aminobutyric acid) stimulation of the metabotropic GABAB receptor results in prolonged inhibition of neurotransmission that is central to brain physiology. GABAB belongs to the Family C of G protein-coupled receptors (GPCRs), which operate as dimers to relay synaptic neurotransmitter signals into a cellular response through the binding and activation of heterotrimeric G proteins. GABAB, however, is unique in its function as an obligate heterodimer in which agonist binding and G protein activation take place on distinct subunits. Here we show structures of heterodimeric and homodimeric full-length GABAB receptors. Complemented by cellular signaling assays and atomistic simulations, the structures reveal an essential role for the GABAB extracellular loop 2 (ECL2) in relaying structural transitions by ordering the linker connecting the extracellular ligand-binding domain to the transmembrane region. Furthermore, the ECL2 of both GABAB subunits caps and interacts with the hydrophilic head of a phospholipid occupying the extracellular half of the transmembrane domain, thereby providing a potentially crucial link between ligand binding and the receptor core that engages G protein. These results provide a starting framework to decipher mechanistic modes of signal transduction mediated by GABAB dimers and have important implications for rational drug design targeting these receptors.

scholarly journals Agonist-specific conformational changes in the yeast alpha-factor pheromone receptor.

1996 ◽  
Vol 16 (9) ◽  
pp. 4818-4823 ◽  
Author(s):  
G Büküşoğlu ◽  
D D Jenness
Keyword(s):  
G Protein ◽  
Conformational Changes ◽  
Transmembrane Helix ◽  
Intracellular Loop ◽  
Cleavage Rate ◽  
Pheromone Receptor ◽  
Protein Activation ◽  
The Third ◽  
Third Intracellular Loop ◽  
Alpha Factor

The yeast alpha-factor pheromone receptor is a member of the G-protein-coupled receptor family. Limited trypsin digestion of yeast membranes was used to investigate ligand-induced conformational changes in this receptor. The agonist, alpha-factor, accelerated cleavage in the third intracellular loop, whereas the antagonist, desTrp1,Ala3-alpha-factor, reduced the cleavage rate. Thus, the enhanced accessibility of the third intracellular loop is specific to the agonist. alpha-Factor inhibited cleavage weakly at a second site near the cytoplasmic terminus of the seventh transmembrane helix, whereas the antagonist showed a stronger inhibition of cleavage at this site and at another site in the C-terminal domain of the receptor. The alpha-factor-induced conformational changes appeared to be inherent properties of the receptor, as they were retained in G-protein-deficient mutants. Moreover, a mutant receptor (ste2-L236H) that affects the third loop and is defective for G-protein coupling retained the ability to undergo the agonist-induced conformational changes. These results are consistent with a model in which G-protein activation is limited by the availability of specific contacts between the G protein and the third intracellular loop of the receptor. The antagonist appears to promote a distinct conformational state that differs from either the unoccupied or the agonist-occupied state.

scholarly journals Structural basis of the activation of the CC chemokine receptor 5 by a chemokine agonist

2020 ◽  
Author(s):  
Polina Isaikina ◽  
Ching-Ju Tsai ◽  
Nikolaus Dietz ◽  
Filip Pamula ◽  
Anne Grahl ◽  
...  
Keyword(s):  
Chemokine Receptor ◽  
Chemokine Receptors ◽  
Binding Mode ◽  
Activation Mechanism ◽  
Structural Basis ◽  
Cc Chemokine ◽  
Gi Protein ◽  
Agonist And Antagonist ◽  
Cc Chemokine Receptor 5 ◽  
Chemokine Receptor 5

AbstractThe human CC chemokine receptor 5 (CCR5) is a G protein-coupled receptor (GPCR) that plays a major role in inflammation and is involved in the pathology of cancer, HIV, and COVID-19. Despite its significance as a drug target, the activation mechanism of CCR5, i.e. how chemokine agonists transduce the activation signal through the receptor, is yet unknown. Here, we report the cryo-EM structure of wild-type CCR5 in an active conformation bound to the chemokine super-agonist [6P4]CCL5 and the heterotrimeric Gi protein. The structure provides the rationale for the sequence-activity relation of agonist and antagonist chemokines. The N-terminus of agonist chemokines pushes onto an aromatic connector that transmits activation to the canonical GPCR microswitch network. This activation mechanism differs significantly from other CC chemokine receptors that bind shorter chemokines in a shallow binding mode and have unique sequence signatures and a specialized activation mechanism.One-sentence summaryThe structure of CCR5 in complex with the chemokine agonist [6P4]CCL5 and the heterotrimeric Gi protein reveals its activation mechanism

scholarly journals GHSR-D2R heteromerization modulates dopamine signaling through an effect on G protein conformation

2018 ◽  
Vol 115 (17) ◽  
pp. 4501-4506 ◽  
Author(s):  
Marjorie Damian ◽  
Véronique Pons ◽  
Pedro Renault ◽  
Céline M’Kadmi ◽  
Bartholomé Delort ◽  
...  
Keyword(s):  
G Protein ◽  
Molecular Processes ◽  
Growth Hormone Secretagogue Receptor ◽  
Growth Hormone Secretagogue ◽  
Α Subunit ◽  
Protein Activation ◽  
Gi Protein ◽  
Dopamine Signaling ◽  
Lipid Environment ◽  
Tetrameric Complex

The growth hormone secretagogue receptor (GHSR) and dopamine receptor (D2R) have been shown to oligomerize in hypothalamic neurons with a significant effect on dopamine signaling, but the molecular processes underlying this effect are still obscure. We used here the purified GHSR and D2R to establish that these two receptors assemble in a lipid environment as a tetrameric complex composed of two each of the receptors. This complex further recruits G proteins to give rise to an assembly with only two G protein trimers bound to a receptor tetramer. We further demonstrate that receptor heteromerization directly impacts on dopamine-mediated Gi protein activation by modulating the conformation of its α-subunit. Indeed, association to the purified GHSR:D2R heteromer triggers a different active conformation of Gαi that is linked to a higher rate of GTP binding and a faster dissociation from the heteromeric receptor. This is an additional mechanism to expand the repertoire of GPCR signaling modulation that could have implications for the control of dopamine signaling in normal and physiopathological conditions.

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