Assembly of JAZ-JAZ and JAZ-NINJA complexes in jasmonate signaling.

Jasmonates (JAs) are plant hormones with crucial roles in development and stress resilience. They activate MYC transcription factors by mediating the proteolysis of MYC inhibitors called JAZ proteins. In the absence of JA, JAZ proteins bind and inhibit MYC through the assembly of MYC-JAZ-Novel Interactor of JAZ (NINJA)-TPL repressor complexes. However, JAZ and NINJA are predicted to be largely intrinsically unstructured, which has precluded their experimental structure determination. Through a combination of biochemical, mutational, and biophysical analyses and AlphaFold-derived ColabFold modeling, we characterized JAZ-JAZ and JAZ-NINJA interactions and generated models with detailed, high-confidence domain interfaces. We demonstrate that JAZ, NINJA, and MYC interface domains are dynamic in isolation and become stabilized in a stepwise order upon complex assembly. By contrast, most JAZ and NINJA regions outside of the interfaces remain highly dynamic and cannot be modeled in a single conformation. Our data indicate that the small JAZ Zinc finger expressed in Inflorescence Meristem (ZIM) motif mediates JAZ-JAZ and JAZ-NINJA interactions through separate surfaces, and our data further suggest that NINJA modulates JAZ dimerization. This study advances our understanding of JA signaling by providing insights into the dynamics, interactions, and structure of the JAZ-NINJA core of the JA repressor complex.

Structures of the entire human opioid receptor family.

Opioids are effective analgesics, but their use is beset by serious side effects, including addiction and respiratory depression, which contribute to the ongoing opioid crisis. The human opioid system contains four opioid receptors (µOR, δOR, κOR, and NOPR) and a set of related endogenous opioid peptides (EOPs), which show distinct selectivity toward their respective opioid receptors (ORs). Despite being key to the development of safer analgesics, the mechanisms of molecular recognition and selectivity of EOPs to ORs remain unclear. Here, we systematically characterize the binding of EOPs to ORs and present five structures of EOP-OR-Gi complexes, including ß-endorphin- and endomorphin-bound µOR, deltorphin-bound δOR, dynorphin-bound κOR, and nociceptin-bound NOPR. These structures, supported by biochemical results, uncover the specific recognition and selectivity of opioid peptides and the conserved mechanism of opioid receptor activation. These results provide a structural framework to facilitate rational design of safer opioid drugs for pain relief.

Structure insights into selective coupling of G protein subtypes by a class B G protein-coupled receptor.

The ability to couple with multiple G protein subtypes, such as Gs, Gi/o, or Gq/11, by a given G protein-coupled receptor (GPCR) is critical for many physiological processes. Over the past few years, the cryo-EM structures for all 15 members of the medically important class B GPCRs, all in complex with Gs protein, have been determined. However, no structure of class B GPCRs with Gq/11 has been solved to date, limiting our understanding of the precise mechanisms of G protein coupling selectivity. Here we report the structures of corticotropin releasing factor receptor 2 (CRF2R) bound to Urocortin 1 (UCN1), coupled with different classes of heterotrimeric G proteins, G11 and Go. We compare these structures with the structure of CRF2R in complex with Gs to uncover the structural differences that determine the selective coupling of G protein subtypes by CRF2R. These results provide important insights into the structural basis for the ability of CRF2R to couple with multiple G protein subtypes.

Molecular recognition of morphine and fentanyl by the human µ-opioid receptor.

Morphine and fentanyl are among the most used opioid drugs that confer analgesia and unwanted side effects through both G protein and arrestin signaling pathways of µ-opioid receptor (µOR). Here, we report structures of the human µOR-G protein complexes bound to morphine and fentanyl, which uncover key differences in how they bind the receptor. We also report structures of µOR bound to TRV130, PZM21, and SR17018, which reveal preferential interactions of these agonists with TM3 side of the ligand-binding pocket rather than TM6/7 side. In contrast, morphine and fentanyl form dual interactions with both TM3 and TM6/7 regions. Mutations at the TM6/7 interface abolish arrestin recruitment of µOR promoted by morphine and fentanyl. Ligands designed to reduce TM6/7 interactions display preferential G protein signaling. Our results provide crucial insights into fentanyl recognition and signaling of µOR, which may facilitate rational design of next-generation analgesics.

Structure and Enzymatic Activity of an Intellectual Disability-Associated Ornithine Decarboxylase Variant, G84R.

Ornithine decarboxylase (ODC) is a rate-limiting enzyme for the synthesis of polyamines (PAs). PAs are required for proliferation, and increased ODC activity is associated with cancer and neural over-proliferation. ODC levels and activity are therefore tightly regulated, including through the ODC-specific inhibitor, antizyme AZ1. Recently, ODC G84R has been reported as a partial loss-of-function variant that is associated with intellectual disability and seizures. However, G84 is distant from both the catalytic center and the ODC homodimerization interface. To understand how G84R modulates ODC activity, we have determined the crystal structure of ODC G84R in both the presence and the absence of the cofactor pyridoxal 5-phosphate. The structures show that the replacement of G84 by arginine leads to hydrogen bond formation of R84 with F420, the last residue of the ODC C-terminal helix, a structural element that is involved in the AZ1-mediated proteasomal degradation of ODC. In contrast, the catalytic center is essentially indistinguishable from that of wildtype ODC. We therefore reanalyzed the catalytic activity of ODC G84R and found that it is rescued when the protein is purified in the presence of a reducing agent to mimic the reducing environment of the cytoplasm. This suggests that R84 may exert its neurological effects not through reducing ODC catalytic activity but through misregulation of its AZ1-mediated proteasomal degradation.

Structural basis of binding and inhibition of ornithine decarboxylase by 1-amino-oxy-3-aminopropane.

Ornithine decarboxylase (ODC) is the rate-limiting enzyme for the synthesis of polyamines (PAs). PAs are oncometabolites that are required for proliferation, and pharmaceutical ODC inhibition is pursued for the treatment of hyperproliferative diseases, including cancer and infectious diseases. The most potent ODC inhibitor is 1-amino-oxy-3-aminopropane (APA). A previous crystal structure of an ODC-APA complex indicated that APA non-covalently binds ODC and its cofactor pyridoxal 5-phosphate (PLP) and functions by competing with the ODC substrate ornithine for binding to the catalytic site. We have revisited the mechanism of APA binding and ODC inhibition through a new crystal structure of APA-bound ODC, which we solved at 2.49 Šresolution. The structure unambiguously shows the presence of a covalent oxime between APA and PLP in the catalytic site, which we confirmed in solution by mass spectrometry. The stable oxime makes extensive interactions with ODC but cannot be catabolized, explaining APA's high potency in ODC inhibition. In addition, we solved an ODC/PLP complex structure with citrate bound at the substrate-binding pocket. These two structures provide new structural scaffolds for developing more efficient pharmaceutical ODC inhibitors.

Structure of an AMPK complex in an inactive, ATP-bound state.

Adenosine monophosphate (AMP)-activated protein kinase (AMPK) regulates metabolism in response to the cellular energy states. Under energy stress, AMP stabilizes the active AMPK conformation, in which the kinase activation loop (AL) is protected from protein phosphatases, thus keeping the AL in its active, phosphorylated state. At low AMP:ATP (adenosine triphosphate) ratios, ATP inhibits AMPK by increasing AL dynamics and accessibility. We developed conformation-specific antibodies to trap ATP-bound AMPK in a fully inactive, dynamic state and determined its structure at 3.5-angstrom resolution using cryo-electron microscopy. A 180° rotation and 100-angstrom displacement of the kinase domain fully exposes the AL. On the basis of the structure and supporting biophysical data, we propose a multistep mechanism explaining how adenine nucleotides and pharmacological agonists modulate AMPK activity by altering AL phosphorylation and accessibility.

Structural insights into the lipid and ligand regulation of serotonin receptors.

Serotonin, or 5-hydroxytryptamine (5-HT), is an important neurotransmitter1,2 that activates the largest subtype family of G-protein-coupled receptors3. Drugs that target 5-HT1A, 5-HT1D, 5-HT1E and other 5-HT receptors are used to treat numerous disorders4. 5-HT receptors have high levels of basal activity and are subject to regulation by lipids, but the structural basis for the lipid regulation and basal activation of these receptors and the pan-agonism of 5-HT remains unclear. Here we report five structures of 5-HT receptor-G-protein complexes: 5-HT1A in the apo state, bound to 5-HT or bound to the antipsychotic drug aripiprazole; 5-HT1D bound to 5-HT; and 5-HT1E in complex with a 5-HT1E- and 5-HT1F-selective agonist, BRL-54443. Notably, the phospholipid phosphatidylinositol 4-phosphate is present at the G-protein-5-HT1A interface, and is able to increase 5-HT1A-mediated G-protein activity. The receptor transmembrane domain is surrounded by cholesterol molecules-particularly in the case of 5-HT1A, in which cholesterol molecules are directly involved in shaping the ligand-binding pocket that determines the specificity for aripiprazol. Within the ligand-binding pocket of apo-5-HT1A are structured water molecules that mimic 5-HT to activate the receptor. Together, our results address a long-standing question of how lipids and water molecules regulate G-protein-coupled receptors, reveal how 5-HT acts as a pan-agonist, and identify the determinants of drug recognition in 5-HT receptors.

Structures of the human dopamine D3 receptor-Gi complexes.

The dopamine system, including five dopamine receptors (D1R-D5R), plays essential roles in the central nervous system (CNS), and ligands that activate dopamine receptors have been used to treat many neuropsychiatric disorders. Here, we report two cryo-EM structures of human D3R in complex with an inhibitory G protein and bound to the D3R-selective agonists PD128907 and pramipexole, the latter of which is used to treat patients with Parkinson's disease. The structures reveal agonist binding modes distinct from the antagonist-bound D3R structure and conformational signatures for ligand-induced receptor activation. Mutagenesis and homology modeling illuminate determinants of ligand specificity across dopamine receptors and the mechanisms for Gi protein coupling. Collectively our work reveals the basis of agonist binding and ligand-induced receptor activation and provides structural templates for designing specific ligands to treat CNS diseases targeting the dopaminergic system.

Structural insights into the human D1 and D2 dopamine receptor signaling complexes.

The D1- and D2-dopamine receptors (D1R and D2R), which signal through Gs and Gi, respectively, represent the principal stimulatory and inhibitory dopamine receptors in the central nervous system. D1R and D2R also represent the main therapeutic targets for Parkinson's disease, schizophrenia, and many other neuropsychiatric disorders, and insight into their signaling is essential for understanding both therapeutic and side effects of dopaminergic drugs. Here, we report four cryoelectron microscopy (cryo-EM) structures of D1R-Gs and D2R-Gi signaling complexes with selective and non-selective dopamine agonists, including two currently used anti-Parkinson's disease drugs, apomorphine and bromocriptine. These structures, together with mutagenesis studies, reveal the conserved binding mode of dopamine agonists, the unique pocket topology underlying ligand selectivity, the conformational changes in receptor activation, and potential structural determinants for G protein-coupling selectivity. These results provide both a molecular understanding of dopamine signaling and multiple structural templates for drug design targeting the dopaminergic system.

Structure of nucleosome-bound DNA methyltransferases DNMT3A and DNMT3B.

CpG methylation by de novo DNA methyltransferases (DNMTs) 3A and 3B is essential for mammalian development and differentiation and is frequently dysregulated in cancer1. These two DNMTs preferentially bind to nucleosomes, yet cannot methylate the DNA wrapped around the nucleosome core2, and they favour the methylation of linker DNA at positioned nucleosomes3,4. Here we present the cryo-electron microscopy structure of a ternary complex of catalytically competent DNMT3A2, the catalytically inactive accessory subunit DNMT3B3 and a nucleosome core particle flanked by linker DNA. The catalytic-like domain of the accessory DNMT3B3 binds to the acidic patch of the nucleosome core, which orients the binding of DNMT3A2 to the linker DNA. The steric constraints of this arrangement suggest that nucleosomal DNA must be moved relative to the nucleosome core for de novo methylation to occur.

Cryo-EM structure of an activated VIP1 receptor-G protein complex revealed by a NanoBiT tethering strategy.

Vasoactive intestinal polypeptide receptor (VIP1R) is a widely expressed class B G protein-coupled receptor and a drug target for the treatment of neuronal, metabolic, and inflammatory diseases. However, our understanding of its mechanism of action and the potential of drug discovery targeting this receptor is limited by the lack of structural information of VIP1R. Here we report a cryo-electron microscopy structure of human VIP1R bound to PACAP27 and Gs heterotrimer, whose complex assembly is stabilized by a NanoBiT tethering strategy. Comparison with other class B GPCR structures reveals that PACAP27 engages VIP1R with its N-terminus inserting into the ligand binding pocket at the transmembrane bundle of the receptor, which subsequently couples to the G protein in a receptor-specific manner. This structure has provided insights into the molecular basis of PACAP27 binding and VIP receptor activation. The methodology of the NanoBiT tethering may help to provide structural information of unstable complexes.

Identification and structural insight of an effective PPARγ modulator with improved therapeutic index for anti-diabetic drug discovery.

Peroxisome proliferator-activated receptor γ (PPARγ) is a key regulator of glucose homeostasis and lipid metabolism, and an important target for the development of modern anti-diabetic drugs. However, current PPARγ-targeting anti-diabetic drugs such as classical thiazolidinediones (TZDs) are associated with undesirable side effects. To address this concern, we here describe the structure-based design, synthesis, identification and detailed in vitro and in vivo characterization of a novel, decanoic acid (DA)-based and selective PPARγ modulator (SPPARγM), VSP-77, especially (S)-VSP-77, as the potential "hit" for the development of improved and safer anti-diabetic therapeutics. We have also determined the co-crystal structure of the PPARγ ligand-binding domain (LBD) in complex with two molecules of (S)-VSP-77, which reveal a previously undisclosed allosteric binding mode. Overall, these findings not only demonstrate the therapeutic advantage of (S)-VSP-77 over current TZD drugs and representative partial agonist INT131, but also provide a rational basis for the development of future SPPARγMs as safe and highly efficacious anti-diabetic drugs.

Structural basis of Fusarium myosin I inhibition by phenamacril.

Fusarium is a genus of filamentous fungi that includes species that cause devastating diseases in major staple crops, such as wheat, maize, rice, and barley, resulting in severe yield losses and mycotoxin contamination of infected grains. Phenamacril is a novel fungicide that is considered environmentally benign due to its exceptional specificity; it inhibits the ATPase activity of the sole class I myosin of only a subset of Fusarium species including the major plant pathogens F. graminearum, F. asiaticum and F. fujikuroi. To understand the underlying mechanisms of inhibition, species specificity, and resistance mutations, we have determined the crystal structure of phenamacril-bound F. graminearum myosin I. Phenamacril binds in the actin-binding cleft in a new allosteric pocket that contains the central residue of the regulatory Switch 2 loop and that is collapsed in the structure of a myosin with closed actin-binding cleft, suggesting that pocket occupancy blocks cleft closure. We have further identified a single, transferable phenamacril-binding residue found exclusively in phenamacril-sensitive myosins to confer phenamacril selectivity.

Cryo-EM Structure of the Human Cannabinoid Receptor CB2-Gi Signaling Complex.

Drugs selectively targeting CB2 hold promise for treating neurodegenerative disorders, inflammation, and pain while avoiding psychotropic side effects mediated by CB1. The mechanisms underlying CB2 activation and signaling are poorly understood but critical for drug design. Here we report the cryo-EM structure of the human CB2-Gi signaling complex bound to the agonist WIN 55,212-2. The 3D structure reveals the binding mode of WIN 55,212-2 and structural determinants for distinguishing CB2 agonists from antagonists, which are supported by a pair of rationally designed agonist and antagonist. Further structural analyses with computational docking results uncover the differences between CB2 and CB1 in receptor activation, ligand recognition, and Gi coupling. These findings are expected to facilitate rational structure-based discovery of drugs targeting the cannabinoid system.

Molecular Basis for Hormone Recognition and Activation of Corticotropin-Releasing Factor Receptors.

Corticotropin-releasing factor (CRF) and the three related peptides urocortins 1-3 (UCN1-UCN3) are endocrine hormones that control the stress responses by activating CRF1R and CRF2R, two members of class B G-protein-coupled receptors (GPCRs). Here, we present two cryoelectron microscopy (cryo-EM) structures of UCN1-bound CRF1R and CRF2R with the stimulatory G protein. In both structures, UCN1 adopts a single straight helix with its N terminus dipped into the receptor transmembrane bundle. Although the peptide-binding residues in CRF1R and CRF2R are different from other members of class B GPCRs, the residues involved in receptor activation and G protein coupling are conserved. In addition, both structures reveal bound cholesterol molecules to the receptor transmembrane helices. Our structures define the basis of ligand-binding specificity in the CRF receptor-hormone system, establish a common mechanism of class B GPCR activation and G protein coupling, and provide a paradigm for studying membrane protein-lipid interactions for class B GPCRs.

Structure-based design of a hyperthermostable AgUricase for hyperuricemia and gout therapy.

Arthrobacter globiformis Uricase (AgUricase) is a homotetrameric uricase with the potential for therapeutic use in treating hyperuricemia-related diseases. To achieve sufficient therapeutic effects, it is essential for this enzyme to have high thermostability and long half-life in physiological condition. To improve the thermostability of this enzyme, we introduced a series of cysteine pair mutations into the AgUricase subunits based on its structural model and studied the thermostability of the mutant enzymes with introduced disulfide bridges. Two intersubunit cysteine pair mutations, K12C-E286C and S296C-S296C, were found to markedly increase the melting temperatures of the corresponding mutant enzymes compared with WT AgUricase. The crystal structure of the K12C-E286C mutant at 1.99 Å resolution confirmed the formation of a distinct disulfide bond between the two subunits in the dimer. Structural analysis and biochemical data revealed that the C-terminal loop of AgUricase was flexible, and its interaction with neighboring subunits was required for the stability of the enzyme. We introduced an additional intersubunit K244C-C302 disulfide bond based on the crystal structure of the K12C-E286C mutant and confirmed that this additional disulfide bond further stabilized the flexible C-terminal loop and improved the thermostability of the enzyme. Disulfide cross-linking also protected AgUricase from protease digestion. Our studies suggest that the introduction of disulfide bonds into proteins is a potential strategy for enhancing the thermostability of multimeric proteins for medical applications.

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

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.