Family reunion of nuclear hormone receptors: structures, diseases, and drug discovery

Geochemical Characteristics and Origin of Sinian-Cambrian Natural Gas in Penglai Gas Area, Sichuan Basin

The Sichuan Basin in southern China is well-known for its large natural gas resource potential stored in Sinian-Cambrian systems. Recently, high-yield industrial gas flow has been discovered from the Dengying Formation (Sinian System) and Canglangpu Formation (Cambrian System) in the Penglai gas area, preluding the multilayer stereoscopic exploration in Sichuan Basin. However, the origin of the natural gas and its preserving mechanics is still debated, and thus, in this study the geochemical characteristics of the natural gas are systematically analyzed, based on the data from gas composition and hydrocarbon isotope of a series of local wells. On this basis, the geochemical characteristics of natural gas in different regions and layers are compared, and the reasons for these differences from the origin and influencing factors are analyzed. The results show the following: (1) The natural gas of the Penglai gas field is dry gas dominated by CH4, and the Sinian Dengying Formation gas has lower C2H6 content, larger dryness coefficient, heavier δ13C, and lighter δ2HCH4 than the Cambrian gas, which is associated with the high proportion of hydrocarbons from the high-maturity Dengying source rocks. (2) The natural gas from some wells in the lower part of the structure is characterized by high H2S content and low CH4 content, and heavy δ13C in the components, which seems to be affected by the thermochemical sulfate reduction (TSR) effect. (3) The natural gas from the Penglai gas area has a relatively low maturity, which appears to be attributed to the continuous sealing ability of the caprock, which can preserve both the early generated gas and the late thermal-cracked gas.

Development and therapeutic potential of allosteric retinoic acid receptor-related orphan receptor γt (RORγt) inverse agonists for autoimmune diseases

The transcription factor retinoic acid receptor-related orphan receptor γt (RORγt) is an attractive drug target for some autoimmune diseases owing to its roles in the differentiation of human T helper 17 (Th17) cells which produce pro-inflammatory cytokine interleukin (IL)-17. RORγt agonists and inverse agonists are classically targeted to the hydrophobic and highly conserved orthosteric binding pocket of RORγt ligand binding domain (LBD). Although successful, this approach also brings some challenges, including off-target effects due to lack of selectivity over other nuclear receptors (NRs). Allosteric regulation of RORγt by synthetic small molecules has recently emerged as novel research interests for its interesting modes of action (MOA), satisfying bioactivity profile and improved selectivity. In this review, we delineated the discovery and identification of the allosteric pocket of RORγt. Subsequently, we focused on examples of small molecules that allosterically inhibit RORγt, with a central attention on structural-activity-relationship (SAR) information, biological activity, pharmacokinetic (PK) property, and the ligand binding mode of these compounds. We also discussed the potential role of RORγt allosteric inverse agonists as small molecule therapeutics for autoimmune diseases.

Ginseng-derived panaxadiol ameliorates STZ-induced type 1 diabetes through inhibiting RORγ/IL-17A axis

Retinoic-acid-receptor-related orphan receptor γ (RORγ) is a major transcription factor for proinflammatory IL-17A production. Here, we revealed that the RORγ deficiency protects mice from STZ-induced Type 1 diabetes (T1D) through inhibiting IL-17A production, leading to improved pancreatic islet β cell function, thereby uncovering a potential novel therapeutic target for treating T1D. We further identified a novel RORγ inverse agonist, ginseng-derived panaxadiol, which selectively inhibits RORγ transcriptional activity with a distinct cofactor recruitment profile from known RORγ ligands. Structural and functional studies of receptor-ligand interactions reveal the molecular basis for a unique binding mode for panaxadiol in the RORγ ligand-binding pocket. Despite its inverse agonist activity, panaxadiol induced the C-terminal AF-2 helix of RORγ to adopt a canonical active conformation. Interestingly, panaxadiol ameliorates mice from STZ-induced T1D through inhibiting IL-17A production in a RORγ-dependent manner. This study demonstrates a novel regulatory function of RORγ with linkage of the IL-17A pathway in pancreatic β cells, and provides a valuable molecule for further investigating RORγ functions in treating T1D.

A Study on Beryl in the Cuonadong Be-W-Sn Polymetallic Deposit, Longzi County, Tibet, China

Recently, aquamarine was discovered in the Cuonadong Be-W-Sn Polymetallic Deposit, Longzi County, Tibet. Longzi aquamarine is being extracted and is expected to be available over the next decade. This study provides a full set of data through standard gemmological properties, including scenes, color characteristics and advanced spectroscopic and chemical analyses, including micro ultraviolet–visible–near-infrared (UV–Vis–NIR), Raman and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The main inclusions in Longzi aquamarine are gas–liquid inclusions and a great number of quartz inclusions. The content of type I H2O is greater than that of type II H2O because of the low-alkali metal content, and “tetrahedral” substitutions and “octahedral” substitutions exist at the same time.

Molecular dynamics simulations on RORγt: insights into its functional agonism and inverse agonism

The retinoic acid receptor-related orphan receptor (ROR) γt receptor is a member of nuclear receptors, which is indispensable for the expression of pro-inflammatory cytokine IL-17. RORγt has been established as a drug target to design and discover novel treatments for multiple inflammatory and immunological diseases. It is important to elucidate the molecular mechanisms of how RORγt is activated by an agonist, and how the transcription function of RORγt is interrupted by an inverse agonist. In this study we performed molecular dynamics simulations on four different RORγt systems, i.e., the apo protein, protein bound with agonist, protein bound with inverse agonist in the orthosteric-binding pocket, and protein bound with inverse agonist in the allosteric-binding pocket. We found that the orthosteric-binding pocket in the apo-form RORγt was mostly open, confirming that apo-form RORγt was constitutively active and could be readily activated (ca. tens of nanoseconds scale). The tracked data from MD simulations supported that RORγt could be activated by an agonist binding at the orthosteric-binding pocket, because the bound agonist helped to enhance the triplet His479-Tyr502-Phe506 interactions and stabilized H12 structure. The stabilized H12 helped RORγt to form the protein-binding site, and therefore made the receptor ready to recruit a coactivator molecule. We also showed that transcription function of RORγt could be interrupted by the binding of inverse agonist at the orthosteric-binding pocket or at the allosteric-binding site. After the inverse agonist was bound, H12 either structurally collapsed, or reorientated to a different position, at which the presumed protein-binding site was not able to be formed.

Modulation of nuclear receptor function: Targeting the protein-DNA interface

Nuclear receptors (NRs) are a superfamily of ligand-dependent transcription factors that modulate several biological processes. Traditionally, modulation of NRs has been focused on the development of ligands that recognize and bind to the ligand binding domain (LBD), resulting in activation or repression of transcription through the recruitment of coregulators. However, for more severe diseases, such as breast and prostate cancer, the conventional treatment addressing LBD modulation is not always successful, due to tumor resistance. To overcome these challenges and aiming to modulate NR activity by inhibiting the NR-DNA interaction, new studies focus on the development of molecules targeting alternative sites and domains on NRs. Here, we discuss two different approaches for this alternative NR modulation: one targeting the NR DNA binding domain (DBD); and the other targeting the DNA sites recognized by NRs. Our aim is to present the challenges and perspectives for developing specific inhibitors for each purpose, alongside with already reported examples.

The nuclear receptor superfamily: A structural perspective

Nuclear receptors (NRs) are a family of transcription factors that regulate numerous physiological processes such as metabolism, reproduction, inflammation, as well as the circadian rhythm. NRs sense changes in lipid metabolite levels to drive differential gene expression, producing distinct physiologic effects. This is an allosteric process whereby binding a cognate ligand and specific DNA sequences drives the recruitment of diverse transcriptional co-regulators at chromatin and ultimately transactivation or transrepression of target genes. Dysregulation of NR signaling leads to various malignances, metabolic disorders, and inflammatory disease. Given their important role in physiology and ability to respond to small lipophilic ligands, NRs have emerged as valuable therapeutic targets. Here, we summarize and discuss the recent progress on understanding the complex mechanism of action of NRs, primarily from a structural perspective. Finally, we suggest future studies to improve our understanding of NR signaling and better design drugs by integrating multiple structural and biophysical approaches.