Biology subjects

Hilger, D.

Publications and source records attributed to Hilger, D..

12 recordsLinked to original sources

bioRxiv2026

Discovery of a Cell-Permeable Gi-Signaling Inhibitor

Heterotrimeric G proteins regulate diverse physiological processes, yet selective small molecule modulators for the Gi subfamily remain scarce. Here, we employed native metabolomics to screen a fungal culture collection for G protein binders, which led to the discovery of N-hydroxyapiosporamide (NHAP), a fungal specialized metabolite that functionally inhibits Gi-signaling. NHAP selectively binds Gi1 and diminishes Gi1-mediated GTP turnover in biochemical assays. In primary ventricular cardiomyocytes, NHAP largely reversed acetylcholine-induced negative inotropy, demonstrating functional Gi-signaling blockade in a physiological context without acute cytotoxicity. This work establishes NHAP as a first-in-class Gi-selective inhibitor, providing a cell-permeable chemical scaffold for the optimization of next-generation agents to control Gi-signaling in cell-based systems and, ultimately, to target Gi1-driven pathologies.

biochemistry↗

bioRxiv2026

Functional diversity of GPCR-Gustducin complexes controls signaling output and suppresses alternative pathways

Gustducin (Ggust), the G protein mediating taste receptor signaling, is expressed not only in sensory taste cells but throughout the human body alongside numerous non-taste G protein-coupled receptors (GPCRs). Whether and how these receptors engage Ggust, and the functional consequences of such interactions, remain poorly understood. Here, we developed two complementary biosensors that enable direct monitoring of GPCR-Ggust interaction and downstream signaling in living cells, allowing pharmacological characterization of Ggust activity by non-taste GPCRs. Unexpectedly, we find that several non-taste GPCRs do not activate Ggust but instead stabilize the G protein heterotrimer and suppress basal signaling by forming unproductive GPCR-G protein complexes, whereas others induce conventional Ggust activation and signal transduction. We further show that these unproductive GPCR-Ggust complexes suppress the activation of alternative signaling pathways by sequestering receptors from other G proteins. This previously unrecognized mode of interaction functionally partitions GPCRs into activators and inactivators of Ggust and represents a mechanism for balancing concurrent signaling pathways within a cell. HighlightsO_LIDevelopment of biosensors for gustducin activation and signal transduction C_LIO_LIAnalysis of single-cell co-expression data of non-tastant GPCRs and gustducin C_LIO_LIProfiling of non-tastant GPCR-induced gustducin activation and signal transduction C_LIO_LIProductive and unproductive GPCR-gustducin complexes revealed C_LIO_LIUnproductive GPCR-gustducin complexes suppress alternative signaling pathways C_LI

cell biology↗

bioRxiv2025

Ligand-dependent G protein dynamics underlying opioid signaling efficacy

Activation of heterotrimeric G proteins by G protein-coupled receptors (GPCRs) requires large-scale opening of the G -helical domain (AHD) to expose the nucleotide-binding site and facilitate GDP-GTP exchange. While orthosteric ligands are known to modulate GPCR conformation and signaling efficacy, how these effects propagate to the G protein itself remains unclear. Using single-molecule fluorescence resonance energy transfer (smFRET) imaging, we monitored AHD motions in Gi proteins coupled to the -opioid receptor (OR) across a spectrum of ligand- and nucleotide-bound states. We find that receptor ligands differentially modulate these dynamics from over 70 [A] away, with higher-efficacy agonists more effectively promoting transitions to an open, low-nucleotide-affinity conformation. These data also capture transient OR-Gi intermediates during nucleotide binding and suggest that -opioid ligand efficacy arises in part from allosteric control over G protein conformational equilibria that kinetically gate activation.

biophysics↗

bioRxiv2025

Cryo-EM structure of a cell-free synthesized full-length human β1-adrenergic receptor in complex with Gs

The third intracellular loop (ICL3) of the {beta}1-adrenergic receptor ({beta}1AR) plays a critical role in regulating G protein coupling, yet the structural basis has remained unclear due to truncations of ICL3 in all available structures of the {beta}1AR in complex with Gs or a G protein mimetic nanobody. To address this, we used cell-free cotranslational insertion of full-length human {beta}1AR into nanodiscs and determined its cryo-EM structure in complex with Gs. In this structure, ICL3 extends transmembrane helix 5, resulting in enhanced interactions with Gs and in a slight rotation of the engaged G protein. This repositioning enables new polar interactions between Gs, ICL2 and helix 8, while ICL1 and helix 8 form additional contacts with G{beta}. These structural insights, supported by mutational analysis, demonstrate that ICL3 enhances G protein activation and downstream cAMP signaling by promoting more extensive interactions between the receptor and the heterotrimeric G protein.

biochemistry↗

bioRxiv2023

Cryo-EM structure of cell-free synthesized human histamine H2 receptor coupled to heterotrimeric Gs protein in lipid nanodisc environment

Here we describe the cryo-electron microscopy structure of the human histamine 2 receptor (H2R) in an active conformation with bound histamine and in complex with Gs heterotrimeric protein at an overall resolution of 3.4 [A]. The complex was generated by cotranslational insertion into preformed nanodisc membranes using cell-free synthesis in E. coli lysates. It is the first structure obtained by this detergent-free strategy and the first GPCR/Gs complex structure in lipid environment. Structural comparison with the inactive conformation of H2R and the inactive and Gq-coupled active state of H1R together with structure-guided functional experiments reveal molecular insights into the specificity of ligand binding and G protein coupling for this receptor family. We demonstrate lipid-modulated folding of cell-free synthesized H2R, its agonist-dependent internalization and its interaction with endogenously synthesized H1R and H2R in HEK293 cells by applying a recently developed nanotransfer technique.

molecular biology↗

bioRxiv2023

Time-resolved cryo-EM of G protein activation by a GPCR

G protein-coupled receptors (GPCRs) activate heterotrimeric G proteins by stimulating the exchange of guanine nucleotide in the G subunit. To visualize this mechanism, we developed a time-resolved cryo-EM approach that examines the progression of ensembles of pre-steady-state intermediates of a GPCR-G protein complex. Using variability analysis to monitor the transitions of the stimulatory Gs protein in complex with the {beta}2-adrenergic receptor ({beta}2AR) at short sequential time points after GTP addition, we identified the conformational trajectory underlying G protein activation and functional dissociation from the receptor. Twenty transition structures generated from sequential overlapping particle subsets along this trajectory, compared to control structures, provide a high-resolution description of the order of events driving G protein activation upon GTP binding. Structural changes propagate from the nucleotide-binding pocket and extend through the GTPase domain, enacting alterations to G Switch regions and the 5 helix that weaken the G protein-receptor interface. Molecular dynamics (MD) simulations with late structures in the cryo-EM trajectory support that enhanced ordering of GTP upon closure of the alpha-helical domain (AHD) against the nucleotide-bound Ras-homology domain (RHD) correlates with irreversible 5 helix destabilization and eventual dissociation of the G protein from the GPCR. These findings also highlight the potential of time-resolved cryo-EM as a tool for mechanistic dissection of GPCR signaling events.

physiology↗

bioRxiv2022

Negative allosteric modulation of the glucagon receptor by RAMP2

Receptor activity-modifying proteins (RAMPs) modulate the activity of many Family B heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs). The glucagon receptor (GCGR), a Family B GPCR responsible for maintenance of proper blood sugar levels, interacts with RAMP2, though the purpose and consequence of this interaction is poorly understood. Using a series of biochemical and cell-based assays, we show that RAMP2 interacts with and broadly inhibits GCGR-induced downstream signaling. Hydrogen-deuterium exchange monitored by mass spectrometry (HDX-MS) demonstrates that RAMP2 enhances local flexibility in select locations in and near the receptor extracellular domain (ECD) as well as at a key region in the 6th transmembrane helix, while single-molecule fluorescence resonance energy transfer (smFRET) experiments show that this RAMP2-induced ECD disorder results in inhibition of active and intermediate states of the intracellular face of the receptor. Using cryo-electron microscopy (cryoEM), we determined the structure of the GCGR-Gs complex at 2.9 [A] resolution in the presence of RAMP2. RAMP2 apparently does not interact with GCGR in an ordered manner, yet the ECD of GCGR is indeed largely disordered in the presence of RAMP2. This disorder is accompanied by rearrangements of several key areas of the receptor, resulting in the formation of a likely unproductive complex. Together, our studies suggest that RAMP2 acts as a negative allosteric modulator of GCGR by enhancing conformational sampling of the ECD.

biochemistry↗

bioRxiv2021

Structures of active melanocortin-4 receptor--Gs-protein complexes with NDP-α-MSH and setmelanotide

The melanocortin-4 receptor (MC4R), a hypothalamic master regulator of energy homeostasis and appetite, is a G-protein coupled receptor and a prime target for the treatment of obesity. Here, we present cryo-electron microscopy structures of MC4R- Gs-protein complexes with two recently FDA-approved drugs, the peptide agonists NDP--MSH and setmelanotide, with 2.9 [A] and 2.6 [A] resolution. Together with signaling data, the complex structures reveal the agonist-induced origin of transmembrane helix (TM) 6 regulated receptor activation. In both structures, different ligand binding modes of NDP--MSH, a high-affinity variant of the endogenous agonist, and setmelanotide, an anti-obesity drug with biased signaling, underline the key role of TM3 for ligand-specific interactions and of calcium ion as a ligand-adaptable cofactor. The agonist-TM3 interplay subsequently impacts the receptor- Gs-protein interfaces, mainly at intracellular loop 2. These structures reveal mechanistic details of MC4R activation or inhibition and provide important insights into receptor selectivity that will facilitate the development of tailored anti-obesity drugs.

biochemistry↗

bioRxiv2019

Uncovering patterns of atomic interactions in static and dynamic structures of proteins

The number of structures and molecular dynamics simulations of proteins is exploding owing to dramatic advances in cryo-electron microscopy, crystallography, and computing. One of the most powerful ways to analyze structural information involves comparisons of interatomic interactions across different structures or simulations of the same protein or related proteins from the same family (e.g. different GPCRs). Such comparative analyses are of interest to a wide range of researchers but currently prove challenging for all but a few. To facilitate comparative structural analyses, we have developed tools for (i) rapidly computing and comparing interatomic interactions and (ii) interactively visualizing interactions to enable structure-based interpretations. Using these tools, we have developed the Contact Comparison Atlas, a web-based resource for the comparative analysis of interactions in structures and simulations of proteins. Using the Contact Comparison Atlas and our tools, we have identified patterns of interactions with functional implications in structures of G-protein-coupled receptors, G proteins and kinases and in the dynamics of muscarinic receptors. The Contact Comparison Atlas can be used to enable structure modeling, drug discovery, protein engineering, and the prediction of disease-associated mutations. Contact Comparison Atlas website: https://getcontacts.github.io/atlas/

biophysics↗

bioRxiv2019

Structural insights into ligand efficacy and activation of the glucagon receptor

The glucagon receptor family comprises Class B G protein-coupled receptors (GPCRs) that play a crucial role in regulating blood sugar levels. Receptors of this family represent important therapeutic targets for the treatment of diabetes and obesity. Despite intensive structural studies, we only have a poor understanding of the mechanism of peptide hormone-induced Class B receptor activation. This process involves the formation of a sharp kink in transmembrane helix 6 that moves out to allow formation of the nucleotide-free G protein complex. Here, we present the cryo-EM structure of the glucagon receptor (GCGR), a prototypical Class B GPCR, in complex with an engineered soluble glucagon derivative and the heterotrimeric G-protein, Gs. Comparison with the previously determined crystal structures of GCGR bound to a partial agonist reveals a structural framework to explain the molecular basis of ligand efficacy that is further supported by mutagenesis data.

biophysics↗

bioRxiv2018

Local membrane charge regulates β2 adrenergic receptor coupling to Gi

G protein coupled receptors (GPCRs) are transmembrane receptors that signal through heterotrimeric G proteins. Lipid modifications anchor G proteins to the plasma membrane; however, little is known about the effect of phospholipid composition on GPCR-G protein coupling. The {beta}2 adrenergic receptor ({beta}2AR) signals through both Gs and Gi in cardiac myocytes where studies suggest that Gi signaling may be cardioprotective. However, Gi coupling is much less efficient than Gs coupling in most cell-based and biochemical assays, making it difficult to study {beta}2AR-Gi interactions. To investigate the role of phospholipid composition on Gs and Gi coupling, we reconstituted {beta}2AR in detergent/lipid mixed micelles and found that negatively charged phospholipids (PS and PG) inhibit {beta}2AR-Gi3 coupling. Replacing negatively charged lipids with neutral lipids (PC or PE) facilitated the formation of a functional {beta}2AR-Gi3 interaction that activated Gi3. Ca2+, known to interact with negatively charged PS, facilitated {beta}2AR-Gi3 interaction in PS. Mutational analysis suggested that Ca2+ interacts with the negatively charged EDGE motif on the carboxyl-terminal end of the N helix of Gi3 and coordinates an EDGE-PS interaction. These results were confirmed in {beta}2AR reconstituted into nanodisc phospholipid bilayers. {beta}2AR-Gi3 interaction was favored in neutral lipids (PE and PC) over negatively charged lipids (PG and PS). In contrast, basal {beta}2AR-Gs interaction was favored in negatively charged lipids over neutral lipids. In negatively-charged lipids, Ca2+ and Mg2+ facilitated {beta}2AR-Gi3 interaction. Taken together, our observations suggest that local membrane charge modulates the interaction between {beta}2AR and competing G protein subtypes.

biochemistry↗

bioRxiv2017

Platform for rapid nanobody discovery in vitro

Camelid single-domain antibody fragments (\"nanobodies\") provide the remarkable specificity of antibodies within a single immunoglobulin VHH domain. This unique feature enables applications ranging from their use as biochemical tools to therapeutic agents. Virtually all nanobodies reported to date have been obtained by animal immunization, a bottleneck restricting many applications of this technology. To solve this problem, we developed a fully in vitro platform for nanobody discovery based on yeast surface display of a synthetic nanobody scaffold. This platform provides a facile and cost-effective method for rapidly isolating nanobodies targeting a diverse range of antigens. We provide a blueprint for identifying nanobodies starting from both purified and non-purified antigens, and in addition, we demonstrate application of the platform to discover rare conformationally-selective nanobodies to a lipid flippase and a G protein-coupled receptor. To facilitate broad deployment of this platform, we have made the library and all associated protocols publicly available.

biochemistry↗