Biology subjects

Thal, D. M.

Publications and source records attributed to Thal, D. M..

13 recordsLinked to original sources

bioRxiv2026

Structural basis of MK-97 positive allosteric modulation at the M4 mAChR

Positive allosteric modulators (PAMs) of the M4 muscarinic acetylcholine receptor (mAChR) represent a promising therapeutic strategy for treating cognitive deficits and neuropsychiatric disorders. While first-generation M4 mAChR PAMs, like LY2033298, demonstrated proof-of-concept, second-generation compounds, such as MK-97, exhibit substantially improved potency and reduced species variability. Here we report the cryo-EM structure of the M4 mAChR bound to the endogenous agonist, acetylcholine, and MK-97 at 2.7 [A] resolution, revealing the molecular basis for improved M4 mAChR PAM activity. MK-97 adopts a distinctive boomerang-shaped conformation within the extracellular-facing allosteric binding site, with a central pyridine vertex, a lower cyclopentylmethylpyrazole arm extending toward the floor of the orthosteric site, and an upper isoindolinone arm projecting toward extracellular loop 2 (ECL2). This extended binding mode establishes a distributed interaction network across transmembrane helices TM2, TM3, TM5, TM6, and TM7, with key contacts including a hydrogen bond with Y922.64 and a {pi}-{pi} stacking interaction with W4357.35. Integration of structural data, molecular dynamics simulations, and mutagenesis validation reveals that the high affinity of MK-97 derives from optimized engagement across all three binding regions rather than dependence on any single critical contact. Insights from comprehensive structure-activity relationship (SAR) studies provide a molecular framework for the rational design of next-generation M4 mAChR PAMs with improved pharmacological properties. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=70 SRC="FIGDIR/small/723386v1_ufig1.gif" ALT="Figure 1"> View larger version (20K): org.highwire.dtl.DTLVardef@75cb90org.highwire.dtl.DTLVardef@1876c9corg.highwire.dtl.DTLVardef@1eba8d0org.highwire.dtl.DTLVardef@9818ad_HPS_FORMAT_FIGEXP M_FIG C_FIG

pharmacology and toxicology↗

bioRxiv2025

Structure-guided allosteric modulation of the delta opioid receptor

Opioid analgesics remain essential for pain management but are associated with significant adverse effects, including respiratory depression, tolerance, and dependence. The {delta}-opioid receptor ({delta}OR) represents a promising therapeutic target for developing safer opioid analgesics with reduced adverse effects compared to conventional -opioid receptor-targeting drugs. Positive allosteric modulators (PAMs) offer advantages over direct agonists by enhancing endogenous opioid signaling while preserving natural spatiotemporal activation patterns, potentially avoiding tolerance and dependence issues. Here, we present high-resolution cryo-EM structures of {delta}OR complexed with the peptide agonist DADLE and the PAM MIPS3614, revealing a novel lipid-facing allosteric binding site formed by transmembrane helices 2, 3, and 4. MIPS3614 stabilizes the active receptor conformation through a critical hydrogen bond with residue N1313.35 in the conserved sodium binding site, a key regulatory region controlling GPCR activation. Comprehensive mutagenesis, molecular dynamics simulations, and structure-activity relationships validate this proposed mechanism. Structure-guided optimization yielded MIPS3983 with enhanced binding affinity and retained cooperativity. Our findings establish the first molecular framework for {delta}OR allosteric modulation and provide a structural foundation for the rational design of safer opioid therapeutics.

pharmacology and toxicology↗

bioRxiv2025

Structural basis for Porcupine inhibition

Wnt signalling is essential for embryonic development and tissue homeostasis, and its dysregulation is associated with multiple types of cancer. Porcupine (PORCN), an endoplasmic reticulum (ER)-resident membrane-bound O-acyltransferase, catalyses the palmitoylation of all 19 human Wnts--a critical modification required for their secretion and activity. This central role makes PORCN an attractive therapeutic target for Wnt-driven cancers, with several inhibitors currently in clinical trials. Here, we present high-resolution cryo-electron microscopy structures of human PORCN in complex with the inhibitors C59 (2.4 [A]) and ETC159 (2.6 [A]), as well as in a ligand-free state (3.3 [A]). These structures reveal critical ordered water molecules that form a hydrogen-bonding network within the active site, mediating inhibitor binding. Our docking simulations of diverse PORCN inhibitors demonstrate that despite their different chemical scaffolds, these compounds adopt similar conformations within the acyl-CoA binding site and are also engaged through a conserved water molecule. Our findings provide a structural foundation for the rational design of next-generation PORCN inhibitors with improved pharmacological properties for cancer therapy.

biochemistry↗

bioRxiv2025

Cryo-EM reveals a new allosteric binding site at the M5 mAChR

The M5 muscarinic acetylcholine receptor (M5 mAChR) represents a promising therapeutic target for neurological disorders. However, the high conservation of its orthosteric binding site has posed significant challenges for drug development. While selective positive allosteric modulators (PAMs) offer a potential solution, a structural understanding of the M5 mAChR and its allosteric binding sites has remained limited. Here, we present a 2.8 [A] cryo-electron microscopy structure of the M5 mAChR complexed with heterotrimeric Gq protein and the agonist iperoxo, completing the active-state structural characterization of the mAChR family. To identify the binding site of M5-selective PAMs, we implemented an integrated approach combining mutagenesis, pharmacological assays, structural biology, and molecular dynamics simulations. Our mutagenesis studies revealed that selective M5 PAMs bind outside previously characterized M5 mAChR allosteric sites. Subsequently, we obtained a 2.1 [A] structure of M5 mAChR co-bound with acetylcholine and the selective PAM VU6007678, revealing a novel allosteric pocket at the extrahelical interface between transmembrane domains 3 and 4 that was confirmed through mutagenesis and simulations. These findings demonstrate the diverse mechanisms of allosteric regulation in mAChRs and highlight the value of integrating pharmacological and structural approaches to identify novel allosteric binding sites.

pharmacology and toxicology↗

bioRxiv2025

Molecular basis of ligand binding and receptor activation at the human A3 adenosine receptor

Adenosine receptors (ARs: A1AR, A2AAR, A2BAR, and A3AR) are crucial therapeutic targets, yet developing selective, efficacious drugs remains challenging. Here, we present high-resolution cryo-electron microscopy (cryo-EM) structures of the human A3AR in three distinct functional states: bound to the endogenous agonist adenosine, the clinically relevant agonist Piclidenoson, and the covalent antagonist LUF7602. These structures, complemented by mutagenesis and pharmacological studies, reveal a unique A3AR activation mechanism involving an extensive hydrogen bond network from the extracellular surface down to the orthosteric binding site. In addition, we identify a cryptic pocket that accommodates the N6-iodobenzyl group of Piclidenoson through a ligand-dependent conformational change of M1745.35. Our comprehensive structural and functional characterization of A3AR advances understanding of adenosine receptor pharmacology and establishes a foundation for developing more selective therapeutics for various disorders including inflammatory diseases, cancer, and glaucoma. TeaserStructures of the A3AR in different conformations reveal a unique activation mechanism and cryptic binding pocket.

pharmacology and toxicology↗

bioRxiv2024

Obtaining high-resolution cryo-EM structures using a common LaB6, 120-keV electron microscope equipped with a sub 200-keV optimised direct electron detector.

Cryo-electron microscopy (Cryo-EM) single particle analysis (SPA) has become a major structural biology technique in recent years. High-resolution cryo-EM typically requires higher voltage cryo-TEMs with coherent FEG sources, stable columns, autoloader systems and direct electron detectors. These setups are specialised for Cryo-EM work and are expensive to establish and maintain. More recently the concept of using 100-keV cryo-TEMs has been introduced as a way to make cryo-EM more affordable and hence accessible to a larger group of researchers. So far, the implementation of these 100-keV cryo-TEMs have relied on specialised microscopes with FEG sources as well as more stable optics than usually present on the common 120-keV TEMs. We here explored whether a standard 120-keV TEM, commonly available at many laboratories worldwide, can be upgraded with a direct electron detector and its suitability for high-resolution cryo-EM using a standard side entry cryo-holder. Using this imaging configuration, we were successful in achieving a 2.65[A] reconstruction for standard apoferritin. We were also able to resolve a more challenging small 64kDa protein haemoglobin to 4.33[A]. Furthermore, we were able to solve an asymmetric 153 kDa membrane protein GPCR (M4 muscarinic acid receptor) to a resolution of 4.4[A]. Importantly, all these results were achieved using a standard automated data collection routine implemented through SerialEM, making it feasible to collect large cryo-EM data sets with a side entry cryo-holder. These results showcase a potentially widely accessible solution to obtaining interpretable cryo-EM structures. Furthermore, we envisage that this imaging configuration gives an option for many EM facilities and laboratories to set up a high-quality cryo-EM SPA sample screening capability without the need to procure costly specialised Cryo-TEMs. This could help to considerably lower the economic entry barrier for cryo-EM SPA and contribute to the "democratisation" of cryo-EM.

biophysics↗

bioRxiv2024

Positive allosteric modulation of a GPCR ternary complex

The activation of a G protein-coupled receptor (GPCR) leads to the formation of a ternary complex between agonist, receptor, and G protein that is characterised by high-affinity binding. Allosteric modulators bind to a distinct binding site from the orthosteric agonist and can modulate both the affinity and the efficacy of orthosteric agonists. The influence allosteric modulators have on the high-affinity active state of the GPCR-G protein ternary complex is unknown due to limitations on attempting to characterize this interaction in recombinant whole cell or membrane-based assays. Here, we use purified M2 muscarinic acetylcholine receptor (mAChR) reconstituted into nanodiscs to show that once the agonist-bound high-affinity state is promoted by the G protein, positive allosteric modulators stabilise the ternary complex that, in the presence of nucleotides leads to an enhanced initial rate of signalling. Our results enhance our understanding of how allosteric modulators influence orthosteric ligand signalling and will aid the design of allosteric therapeutics. TeaserAllostery from top and bottom, the combined influence of positive allosteric modulators on receptor signalling.

pharmacology and toxicology↗

bioRxiv2024

Structural insights into the human P2X1 receptor and ligand interactions

The P2X1 receptor is a trimeric ligand-gated ion channel that plays a pivotal role in urogenital and immune functions. Consequently, it offers numerous potential indications for novel drug treatments. Unfortunately, the progress of drug discovery targeting the P2X1 receptor has been impeded by the absence of structural information. To gain deeper insights into the binding site of the P2X1 receptor, we employed cryogenic electron microscopy (cryo-EM) to elucidate the structures of the P2X1 receptor in both an ATP-bound desensitised state and an NF449-bound closed state. NF449 is a potent P2X1 receptor antagonist and engages with the receptor in a distinctive manner. To gain insights into the molecular machinery governing receptor inhibition and activation and better understand P2X1 receptor ligand subtype selectivity, critical P2X1 receptor residues involved in ligand binding were mutated. Radioligand binding assays with [3H]-,{beta}-methylene ATP and intracellular calcium influx were employed to assess the effect of these mutations on ligand binding and receptor activation, thereby validating key ligand-receptor interactions. This research expands our understanding of the P2X1 receptor structure at a molecular level and opens new avenues for in silico drug design targeting the P2X1 receptor.

pharmacology and toxicology↗

bioRxiv2023

Cryo-EM structures of human arachidonate 12S-Lipoxygenase (12-LOX) bound to endogenous and exogenous inhibitors

Human 12-lipoxygenase (12-LOX) is an enzyme involved in platelet activation and is a promising target for antiplatelet therapies. Despite the clinical importance of 12-LOX, the exact mechanisms of how it affects platelet activation are unclear, and the lack of structural information has limited drug discovery efforts. In this study, we used single-particle cryoelectron microscopy to determine the high-resolution structures (1.7 [A] - 2.8 [A]) of human 12-LOX for the first time. Our results showed that 12-LOX can exist in multiple oligomeric states, from monomer to hexamer, which may impact its catalytic activity and membrane association. We also identified different conformations within a 12-LOX dimer, likely representing different time points in its catalytic cycle. Furthermore, we were able to identify small molecules bound to the 12-LOX structures. The active site of the 12-LOX tetramer is occupied by an endogenous 12-LOX inhibitor, a long-chain acyl-Coenzyme A. Additionally, we found that the 12-LOX hexamer can simultaneously bind to arachidonic acid and ML355, a selective 12-LOX inhibitor that has passed a phase I clinical trial for treating heparin-induced thrombocytopenia and has received fast-track designation by the FDA. Overall, our findings provide novel insights into the assembly of 12-LOX oligomers, its catalytic mechanism, and small molecule binding, paving the way for further drug development targeting the 12-LOX enzyme. Key PointsO_LIThe first full-length structures of human arachidonate 12S-Lipoxygenase (12-LOX) C_LIO_LIReveals mechanisms of oligomeric and conformational states C_LIO_LIUncovers natural inhibitor of 12S-Lipoxygenase (12-lox) C_LIO_LIReveals a binding site of inhibitor ML355 C_LI

biochemistry↗

bioRxiv2022

Pharmacological hallmarks of allostery at the M4 muscarinic receptor elucidated through structure and dynamics

Allosteric modulation of G protein-coupled receptors (GPCRs) is a major paradigm in drug discovery. Despite decades of research, a molecular level understanding of the general principals that govern the myriad pharmacological effects exerted by GPCR allosteric modulators remains limited. The M4 muscarinic acetylcholine receptor (M4 mAChR) is a well-validated and clinically relevant allosteric drug target for several major psychiatric and cognitive disorders. Here, we present high-resolution cryo-electron microscopy structures of the M4 mAChR bound to a cognate Gi1 protein and the high affinity agonist, iperoxo, in the absence and presence of two different positive allosteric modulators, LY2033298 or VU0467154. We have also determined the structure of the M4 mAChR-Gi1 complex bound to its endogenous agonist, acetylcholine (ACh). Structural comparisons, together with molecular dynamics, mutagenesis, and pharmacological validations, have provided in-depth insights into the role of structure and dynamics in orthosteric and allosteric ligand binding, global mechanisms of receptor activation, cooperativity, probe-dependence, and species variability; all key hallmarks underpinning contemporary GPCR drug discovery.

pharmacology and toxicology↗

bioRxiv2021

Selective G protein signaling driven by Substance P-Neurokinin Receptor structural dynamics

The neuropeptide Substance P (SP) is important in pain and inflammation. SP activates the neurokinin-1 receptor (NK1R) to signal via Gqand Gs proteins. Neurokinin A also activates NK1R, but leads to selective Gq signaling. How two stimuli yield distinct G-protein signaling at the same G-protein-coupled-receptor remains unclear. We determined cryo-EM structures of active NK1R bound to SP or the Gq-biased peptide SP6-11. Peptide interactions deep within NK1R are critical for receptor activation. Conversely, interactions between SP and NK1R extracellular loops are required for potent Gs signaling but not Gq signaling. Molecular dynamics simulations showed that these superficial contacts restrict SP flexibility deep in the NK1R pocket. SP6-11, which lacks these interactions, is dynamic while bound to NK1R. Structural dynamics of NK1R agonists therefore depend on interactions with the receptor extracellular loops and regulate G-protein signaling selectivity. Similar interactions between other neuropeptides and their cognate receptors may tune intracellular signaling.

biochemistry↗

bioRxiv2021

Structures of the human cholecystokinin 1 (CCK1) receptor bound to Gs and Gq mimetic proteins: insight into mechanisms of G protein selectivity

G protein-coupled receptors (GPCRs) are critical regulators of cellular function acting via heterotrimeric G proteins as their primary transducers with individual GPCRs capable of pleiotropic coupling to multiple G proteins. Structural features governing G protein selectivity and promiscuity are currently unclear. Here we used cryo-electron microscopy to determine structures of the CCK1R bound to the CCK peptide agonist, CCK-8 and two distinct transducer proteins, its primary transducer Gq, and the more weakly coupled Gs. As seen with other Gq/11-GPCR complexes, the Gq-5 helix bound to a relatively narrow pocket in the CCK1R core. Surprisingly, the backbone of the CCK1R and volume of the G protein binding pocket was essentially equivalent when Gs was bound, with the Gs 5 helix displaying a conformation that arises from "unwinding" of the far C-terminal residues, compared to canonically Gs coupled receptors. Thus, integrated changes in the conformations of both the receptor and G protein play critical roles in the promiscuous coupling of individual GPCRs. One-Sentence SummaryCryo-EM structures of the CCK-1R reveal key mechanisms for promiscuous G protein coupling.

pharmacology and toxicology↗

bioRxiv2019

Crystal structure of the M5 muscarinic acetylcholine receptor

The human M5 muscarinic acetylcholine receptor (mAChR) has recently emerged as an exciting therapeutic target for treating a range of disorders, including drug addiction. However, a lack of structural information for this receptor subtype has limited further drug development and validation. Here we report a high-resolution crystal structure of the human M5 mAChR bound to the clinically used inverse agonist, tiotropium. This structure allowed for a comparison across all five mAChR family members that revealed important differences in both orthosteric and allosteric sites that could inform the rational design of selective ligands. These structural studies together with chimeric swaps between the extracellular regions of the M2 and M5 mAChR further revealed the structural insight into \"kinetic-selectivity\", where ligands show differential residency times between related family members. Collectively, our study provides important insights into the nature of orthosteric and allosteric ligand interaction across the mAChR family that could be exploited for the design of selective ligands.\n\nSignificance StatementThe five subtypes of the muscarinic acetylcholine receptors (mAChRs) are expressed throughout the central and peripheral nervous system where they play a vital role in physiology and pathologies. Recently, the M5 mAChR subtype has emerged as an exciting drug target for the treatment of drug addiction. We have determined the atomic structure of the M5 mAChR bound to the clinically used inverse agonist tiotropium. The M5 mAChR structure now allows for a full comparison of all five mAChR subtypes and reveals subtle differences in the extracellular loop (ECL) regions of the receptor that mediate orthosteric and allosteric ligand selectivity. Together these findings open the door for future structure-based design of selective drugs that target this therapeutically important class of receptors.

pharmacology and toxicology↗