Ligand Binding Ability Research Articles

A class-A GPCR solubilized under high hydrostatic pressure retains its ligand binding ability

The effect of high hydrostatic pressure (HHP) on the solubilization of a class-A G protein-coupled receptor, the silkmoth pheromone biosynthesis-activating neuropeptide receptor (PBANR), was investigated. PBANR was expressed in expresSF+ insect cells as a C-terminal fusion protein with EGFP. The membrane fraction was subjected to HHP treatment (200MPa) at room temperature for 1–16h in the presence of 0–2.0% (w/v) n-dodecyl-β-D-maltopyranoside (DDM). The solubilization yield of PBANR-EGFP in the presence of 0.6% (w/v) DDM increased to ~1.5-fold after 1h HHP treatment. Fluorescence-detection size-exclusion chromatography demonstrated that the PBANR-EGFP ligand binding ability was retained after HHP-mediated solubilization. The PBANR-EGFP solubilized with 1.0% DDM under HHP at room temperature for 6h retained ligand binding ability, whereas solubilization in the absence of HHP treatment resulted in denaturation.

Rational engineering of the CDK9/CyclinT complex improves protein stability enabling kinetic analysis of inhibitors by SPR

Inhibition of CDK9, an enzyme that regulates transcriptional elongation, can lead to apoptosis in cancer cells. Thus CDK9 inhibitors are potential new anti‐cancer agents. In order to more fully characterize novel CDK9 inhibitors that we are developing we wanted to be able to perform kinetic analyses including the determination of kinetic on and off rates. The CDK9/CyclinT kinase domain exhibited rapid loss of ligand binding ability when immobilized on a SPR chip, preventing collection of kinetic data. To improve stability, a series of amino acid changes were made based on the crystal structure. These included surface residue changes of both the CDK9 kinase domain and Cyclin T, and combinations of the various changes (up to 7 changes in CDK9 and 5 in Cyclin T). Modified genes were synthesized, a matrix of modified CDK9 and cyclin T combinations defined (18 conditions) and expressed in insect cells. Constructs were evaluated by expression levels, purification yield, ability to concentrate protein to high levels, increased melting temperature, conjugation and stability during SPR. The original CDK9/Cyclin T complex lost activity minutes after conjugation to the SPR chip whereas the “thermostabilized” CDK9 (7 residue modified) Cyclin T (5 residue modified) complex is active for 2.5 days after immobilization allowing for determination of on and off rates of CDK9 Cyclin T inhibitors.

Challenge of mimicking the influences of the cellular environment on RNA structure by PEG-induced macromolecular crowding.

There are large differences between the cellular environment and the conditions widely used to study RNA in vitro. SHAPE RNA structure probing in Escherichia coli cells has shown that the cellular environment stabilizes both long-range and local tertiary interactions in the adenine riboswitch aptamer domain. Synthetic crowding agents are widely used to understand the forces that stabilize RNA structure and in efforts to recapitulate the cellular environment under simplified experimental conditions. Here, we studied the structure and ligand binding ability of the adenine riboswitch in the presence of the macromolecular crowding agent, polyethylene glycol (PEG). Ethylene glycol and low-molecular mass PEGs destabilized RNA structure and caused the riboswitch to sample secondary structures different from those observed in simple buffered solutions or in cells. In the presence of larger PEGs, longer-range loop-loop interactions were more similar to those in cells than in buffer alone, consistent with prior work showing that larger PEGs stabilize compact RNA states. Ligand affinity was weakened by low-molecular mass PEGs but increased with high-molecular mass PEGs, indicating that PEG cosolvents exert complex chemical and steric effects on RNA structure. Regardless of polymer size, however, nucleotide-resolution structural characteristics observed in cells were not recapitulated in PEG solutions. Our results reveal that the cellular environment is difficult to recapitulate in vitro; mimicking the cellular state will likely require a combination of crowding agents and other chemical species.

GIGYF2 mutation in late-onset Parkinson's disease with cognitive impairment.

Although in the last two decades there has been considerable progress in understanding the genetic basis of Parkinson’s disease (PD), the majority of PD is sporadic and its genetic causes are largely unknown. In an attempt to identify novel genetic causes of PD, whole exome sequencing and subsequent analyses were performed in a family featuring late-onset PD with cognitive impairment. A novel genetic variant (p.Arg610Gly) in the GIGYF2 gene, previously known to be associated with PD, was identified as potential disease-causing mutation. The GIGYF2 p.Arg610Gly mutation situated in the GYF domain of the encoding protein was predicted to be pathogenic and to disrupt the GYF’s ligand–binding abilities. While further research is still required, this finding may shed light on the GIGYF2-associated mechanisms that lead to PD and suggests insulin dysregulation as a disease-specific mechanism for both PD and cognitive dysfunction.

G Protein-Coupled Receptor 87: a Promising Opportunity for Cancer Drug Discovery.

G protein-coupled receptors (GPRs) constitute one of the largest families of membrane proteins encoded by the human genome. Upon binding to various ligands, these seven-transmembrane receptors play an essential role in many physiological processes, including neurotransmission, immunity, inflammation, regulation of mood and behavior. In view of their important functions, aberrant expression and activity of GPRs have been implicated in a wide spectrum of diseases, including tumorigenesis. GPR87, a cell surface GPR related to the LPA receptor family, is overexpressed in diverse carcinomas and plays an essential role in tumor cell survival. In our recent work, we uncovered that GPR87 expression is regulated by the tumor suppressor p53 and by DNA damage in a p53-dependent manner. Moreover, we found that a lack of GPR87 triggers an increase in p53, concomitant with a decrease in Akt, which results in the sensitization of tumor cells to DNA damage-induced apoptosis and growth suppression. Altogether, we uncovered an essential function for GPR87 in p53-dependent cell survival in response to stress signals. Due to their unique structure, localization and ligand binding ability, GPRs have been extensively used for drug development and are the most common targets of commercial drugs. Although studies are required to determine GPR87 natural ligand(s) and signaling pathways, GPR87 is undoubtedly a very promising novel target for cancer prevention and treatment.

Notch Receptor-Ligand Engagement Maintains Hematopoietic Stem Cell Quiescence and Niche Retention.

Notch is long recognized as a signaling molecule important for stem cell self-renewal and fate determination. Here, we reveal a novel adhesive role of Notch-ligand engagement in hematopoietic stem and progenitor cells (HSPCs). Using mice with conditional loss of O-fucosylglycans on Notch EGF-like repeats important for the binding of Notch ligands, we report that HSPCs with faulty ligand binding ability display enhanced cycling accompanied by increased egress from the marrow, a phenotype mainly attributed to their reduced adhesion to Notch ligand-expressing stromal cells and osteoblastic cells and their altered occupation in osteoblastic niches. Adhesion to Notch ligand-bearing osteoblastic or stromal cells inhibits wild type but not O-fucosylglycan-deficient HSPC cycling, independent of RBP-JK -mediated canonical Notch signaling. Furthermore, Notch-ligand neutralizing antibodies induce RBP-JK -independent HSPC egress and enhanced HSPC mobilization. We, therefore, conclude that Notch receptor-ligand engagement controls HSPC quiescence and retention in the marrow niche that is dependent on O-fucosylglycans on Notch.

Mechanisms of tumor-promoting activities of nicotine in lung cancer: synergistic effects of cell membrane and mitochondrial nicotinic acetylcholine receptors.

BackgroundOne of the major controversies of contemporary medicine is created by an increased consumption of nicotine and growing evidence of its connection to cancer, which urges elucidation of the molecular mechanisms of oncogenic effects of inhaled nicotine. Current research indicates that nicotinergic regulation of cell survival and death is more complex than originally thought, because it involves signals emanating from both cell membrane (cm)- and mitochondrial (mt)-nicotinic acetylcholine receptors (nAChRs). In this study, we elaborated on the novel concept linking cm-nAChRs to growth promotion of lung cancer cells through cooperation with the growth factor signaling, and mt-nAChRs — to inhibition of intrinsic apoptosis through prevention of opening of mitochondrial permeability transition pore (mPTP).MethodsExperiments were performed with normal human lobar bronchial epithelial cells, the lung squamous cell carcinoma line SW900, and intact and NNK-transformed immortalized human bronchial cell line BEP2D.ResultsWe demonstrated that the growth-promoting effect of nicotine mediated by activation of α7 cm-nAChR synergizes mainly with that of epidermal growth factor (EGF), α3 — vascular endothelial growth factor (VEGF), α4 — insulin-like growth factor I (IGF-I) and VEGF, whereas α9 with EGF, IGF-I and VEGF. We also established the ligand-binding abilities of mt-nAChRs and demonstrated that quantity of the mt-nAChRs coupled to inhibition of mPTP opening increases upon malignant transformation.ConclusionsThese results indicated that the biological sum of simultaneous activation of cm- and mt-nAChRs produces a combination of growth-promoting and anti-apoptotic signals that implement the tumor-promoting action of nicotine on lung cells. Therefore, nAChRs may be a promising molecular target to arrest lung cancer progression and re-open mitochondrial apoptotic pathways.

A hotspot in the glucocorticoid receptor DNA-binding domain susceptible to loss of function mutation

Glucocorticoids (GCs) are used to treat a variety of inflammatory disorders and certain cancers. However, GC resistance occurs in subsets of patients. We found that EL4 cells, a GC-resistant mouse thymoma cell line, harbored a point mutation in their GC receptor (GR) gene, resulting in the substitution of arginine 493 by a cysteine in the second zinc finger of the DNA-binding domain. Allelic discrimination analyses revealed that the R493C mutation occurred on both alleles. In the absence of GCs, the GR in EL4 cells localized predominantly in the cytoplasm and upon dexamethasone treatment underwent nuclear translocation, suggesting that the ligand binding ability of the GR in EL4 cells was intact. In transient transfection assays, the R493C mutant could not transactivate the MMTV-luciferase reporter. Site-directed mutagenesis to revert the R493C mutation restored the transactivation activity. Cotransfection experiments showed that the R493C mutant did not inhibit the transcriptional activities of the wild-type GR. In addition, the R493C mutant did not repress either the AP-1 or NF-κB reporters as effectively as WT GR. Furthermore, stable expression of the WT GR in the EL4 cells enabled GC-mediated gene regulation, specifically upregulation of IκBα and downregulation of interferon γ and interleukin 17A. Arginine 493 is conserved among multiple species and all human nuclear receptors and its mutation has also been found in the human GR, androgen receptor, and mineralocorticoid receptor. Thus, R493 is necessary for the transcriptional activity of the GR and a hotspot for mutations that result in GC resistance.

Insights into structure and function of human PWWP domains

The PWWP domain is a small structural unit that can bind both DNA and histone, hence involved in chromatin targeting. Here we summarize the structural feature s of the human PWWP domains and highlight their ligand binding ability from a structural view. Their assoc iation with biological functions is also discussed.

Global Shape and Ligand Binding Efficiency of the HIV-1-neutralizing Antibodies Differ from Those of Antibodies That Cannot Neutralize HIV-1

Asymmetric disposition of Fab arms in the structures solved for the broadly neutralizing monoclonal antibody (nmAb) IgG1 b12 raised the question of whether the unusual shape observed for b12 is common for all IgG1 mAbs or if there is a difference in the overall shape of nmAbs versus non-nmAbs. We compared small angle x-ray scattering (SAXS) data-based models and limited proteolysis profiles of some IgG1 mAbs known to be having and lacking HIV-1 neutralizing potency. In non-nmAbs, the Fab arms were found to be symmetrically disposed in space relative to central Fc, but in most nmAbs, the Fab arms were asymmetrically disposed, as seen for IgG1 b12. The only exceptions were 2G12 and 4E10, where both Fab arms were closed above Fc, suggesting some Fab-Fc and/or Fab-Fab interaction in the nmAbs that constrained extension of the Fab-Fc linker. Interestingly, these observations were correlated with differential proteolysis profiles of the mAbs by papain. Under conditions when papain could cut both Fab arms of non-nmAbs, only one Fab arm could be removed from neutralizing ones (except for 2G12 and 4E10). Chromatography and small angle x-ray scattering results of papain-digested products revealed that 1) the Fab-Fc or Fab-Fab interactions in unliganded mAbs are retained in digested products, and 2) whereas anti-gp120 non-nmAbs could bind two gp120 molecules, nmAbs could bind only one gp120. Additional experiments showed that except for 2G12 and 4E10, unopen shapes of nmAbs remain uninfluenced by ionic strength but can be reversibly opened by low pH of buffer accompanied by loss of ligand binding ability.

In vitro hemocompatibility and toxic mechanism of graphene oxide on human peripheral blood T lymphocytes and serum albumin.

Graphene oxide (GO) has shown tremendous application potential as a biomedical material. However, its interactions with blood components are not yet well understood. In this work, we assess the toxicity of pristine GO (p-GO) and functionalized GO (GO-COOH and GO-PEI) to primary human peripheral blood T lymphocytes and human serum albumin (HSA), and also study the underlying toxic mechanism. Our results indicate that p-GO and GO-COOH have good biocompatibility to T lymphocytes at the concentration below 25 μg mL(-1), but notable cytotoxicity above 50 μg mL(-1). By contrast, GO-PEI exhibits significant toxicity even at 1.6 μg mL(-1). Further investigations show that although p-GO does not enter into the cell or damage the membrane, its presence leads to the increase in reactive oxygen species (ROS), moderate DNA damage, and T lymphocyte apoptosis. Interestingly, little effect on T lymphocyte immune response suppression is observed in this process despite p-GO inflicting cell apoptosis. The toxic mechanism is that p-GO interacts directly with the protein receptors to inhibit their ligand-binding ability, leading to ROS-dependent passive apoptosis through the B-cell lymphoma-2 (Bcl-2) pathway. Compared with p-GO, GO-COOH exhibits a similar toxic effect on T lymphocytes except keeping a normal ROS level. A proposed toxic mechanism is that GO-COOH inhibits protein receptor-ligand binding, and passes the passive apoptosis signal to nucleus DNA through a ROS-independent mechanism. On the other hand, GO-PEI shows severe hematotoxicity to T lymphocytes by inducing membrane damage. For plasma protein HSA, the binding of GO-COOH results in minimal conformational change and HSA's binding capacity to bilirubin remains unaffected, while the binding of p-GO and GO-PEI exhibits strong toxicity on HSA. These findings on the interactions of two-dimensional nanomaterials and biological systems, along with the enquiry of the mechanisms, would provide essential support for further safety evaluation of the biomedical applications of GO.

The ligand binding ability of dopamine D1 receptors synthesized using a wheat germ cell-free protein synthesis system with liposomes

G-protein coupled receptors (GPCRs) share a common seven-transmembrane topology and mediate cellular responses to a variety of extracellular signals. However, structural and functional approaches to GPCRs have often been limited by the difficulty of producing a sufficient amount of receptor protein using conventional expression systems. We synthesized human dopamine D1 receptors using a wheat cell-free protein synthesis system with liposomes and then analyzed their receptor binding ability. We determined the specific binding of [3H]SCH23390 to the synthesized receptors generated from a cell-free protein synthesis system or rat striatal membranes. From Scatchard plot analysis, the dissociation constant (Kd) and the maximum density (Bmax) of the synthesized receptors were 6.61±0.06nM and 1.85±0.05pmol/mg protein, respectively. The same analysis for rat striatal membrane gave a Kd of 2.67±0.05nM and Bmax of 0.70±0.10pmol/mg protein. Using a competition binding assay, Ki values of antagonists, SCH23390, LE300 and SKF83566, for the synthetic receptors were the same as those for rat striatal membranes, but Ki values of agonists, A68930, SKF38393 and dopamine, were 5–17 fold higher than those for rat striatal membranes. These results suggest that the dopamine D1 receptors synthesized in liposomes have a functional binding capacity. The different patterns of binding of antagonists and agonists to the synthetic receptors and rat striatal membranes indicate that G proteins are involved in agonist binding to dopamine D1 receptors. The cell-free protein synthesis method with liposomes will be invaluable for the functional analysis of GPCRs.

Allosteric Regulation of the Ligand-Binding Ability of Zinc Porphyrins with Sterically Bulky Shielding Units by Metal Complexation

Abstract An artificial allosteric system composed of a zinc porphyrin moiety as a ligand-binding site, diphenylanthracene moieties as sterically bulky shielding units, and bipyridine terminals as Fe(II) ion-binding sites, was designed, synthesized, and characterized. The allosteric system forms an [Fe(bpy)3]-type complex in the presence of Fe(II) ions and induces a large conformational change in the alkyl side chains and shielding units, in which the anthracene groups would cover both the top and bottom of the porphyrin Zn(II) center. Consequently, the ligand-binding ability of the zinc porphyrin unit was allosterically suppressed. We found that the formation of the Fe(II) complex resulted in a 9.5-fold reduction in the binding constant between the zinc porphyrin and 3,5-bis(3,5-di-tert-butylphenyl)pyridine at 20 °C. Comparisons of entropy and enthalpy changes in the absence and presence of Fe(II) ions led to the conclusion that the allosteric suppression was mainly due to the destabilization of the Zn(II)-coordinated complex owing to the steric repulsion between the ligand and the shielding unit.

Elucidation of differences in N-glycosylation between different molecular weight forms of recombinant CLEC-2 by LC MALDI tandem MS

C-type lectin-like receptor 2 (CLEC-2) is a newly identified receptor expressed on the platelet surface. It has been reported that CLEC-2 exists as a higher molecular weight (HMW) and a lower molecular weight (LMW) form, which share the same protein core but differ in glycans. The two forms appear to have different ligand-binding abilities, indicating that the differential glycosylation of CLEC-2 possibly produces functionally distinct glycoforms. This study aimed to explore an easy method to directly elucidate the N-glycosylation difference by employing a glycoproteomics approach. The off-line coupling of nano-LC with a MALDI-QIT-TOF mass spectrometer was demonstrated to be capable of sensitive and direct elucidation of the glycosylation difference between HMW and LMW CLEC-2, simultaneously providing information about their oligosaccharide structures and the glycosylation sites. The results reveal that a specific glycosylation site, Asn 134, is differently glycosylated in the two forms, with complex types of bi-antennary, tri-antennary and tetra-antennary, N-linked, fucosylated glycans identified at this site in the HMW form but not in the LMW form. The observed difference in glycosylation might provide new insights into the underlying mechanisms of biological functions of CLEC-2. Because of its simplicity and sensitivity, the method explored in this work suggests that it holds promise as a method of elucidating differences in direct N-glycosylation of target glycoprotein, even in small amount of samples.

Analytical strategies based on quantum dots for heavy metal ions detection.

Heavy metal contamination is one of the major concerns to human health because these substances are toxic and retained by the ecological system. Therefore, in recent years, there has been a pressing need for fast and reliable methods for the analysis of heavy metal ions in environmental and biological samples. Quantum dots (QDs) have facilitated the development of sensitive sensors over the past decade, due to their unique photophysical properties, versatile surface chemistry and ligand binding ability, and the possibility of the encapsulation in different materials or attachment to different functional materials, while retaining their native luminescence property. This paper comments on different sensing strategies with QD for the most toxic heavy metal ions (i.e., cadmium, Cd2+; mercury, Hg2+; and lead, Pb2+). Finally, the challenges and outlook for the QD-based sensors for heavy metals ions are discussed.

Testing the versatility of the alternating sites of reactivity mechanism in the phosphagen kinases (768.11)

Phosphagen kinases achieve “buffering” of cellular ATP levels by catalyzing the reversible transfer of a phosphoryl group from ATP to a guanidino acceptor to form a high energy compound, phosphagen. Creatine kinase (CK), a PK found mainly in vertebrates, exists as a dimer in muscles; whereas, arginine kinase (AK), found exclusively in invertebrates, exists mainly as a monomer. The physiological functions of different oligomerization states within the PK family are not fully understood. Crystal structures of dimeric CK and AK are consistent with cooperativity in ligand binding between the two subunits. Based on these results, a reciprocating mechanism of catalysis was suggested for dimeric PKs. However, the exact mechanism and the potential effects of negative cooperativity on ligand binding ability of dimeric PKs remains unexplained. In this study, we’ve shown direct functional evidence of negative cooperativity in rabbit muscle CK (rbCK) by measuring the enzymes’ affinity for MgADP using isothermal titration calorimetry. Measurements of rbCK‐ligand interactions, in presence of saturating concentrations of creatine and nitrate, to form the transition‐state analogue quaternary complex, were fitted using a two‐site binding model with Kd1 = 56 ± 32 µM and Kd2 = 2.7 ± 1.4 mM. In the absence of creatine and nitrate, MgADP binding by rbCK fits a one‐site binding model, with Kd = 720 ± 330 µM. These suggest that the presence of creatine enables the conformation necessary to permit cross‐talk between the subunits. Pre‐steady state kinetic assays and the effect of viscosity on kcat show that the rate‐limiting step of reaction catalyzed by PKs is dependent on the oligomerization state of the enzyme, consistent with the alternating site of reactivity mechanism.Grant Funding Source: NSF Grant #0619123

Pattern recognition scavenger receptor A/CD204 regulates airway inflammatory homeostasis following organic dust extract exposures

Exposure to agriculture organic dusts, comprised of a diversity of pathogen-associated molecular patterns, results in chronic airway diseases. The multi-functional class A macrophage scavenger receptor (SRA)/CD204 has emerged as an important class of pattern recognition receptors with broad ligand binding ability. The objective was to determine the role of SRA in mediating repetitive and post-inflammatory organic dust extract (ODE)-induced airway inflammation. Wild-type (WT) and SRA knockout (KO) mice were intra-nasally treated with ODE or saline daily for 3 weeks and immediately euthanized or allowed to recover for 1 week. Results show that lung histopathologic changes were increased in SRA KO mice as compared to WT following repetitive ODE exposures marked predominately by increased size and distribution of lymphoid aggregates. After a 1-week recovery from daily ODE treatments, there was significant resolution of lung injury in WT mice, but not SRA KO animals. The increased lung histopathology induced by ODE treatment was associated with decreased accumulation of neutrophils, but greater accumulation of CD4+ T-cells. The lung cytokine milieu induced by ODE was consistent with a TH1/TH17 polarization in both WT and SRA KO mice. Overall, the data demonstrate that SRA/CD204 plays an important role in the normative inflammatory lung response to ODE, as evidenced by the enhanced dust-mediated injury viewed in the absence of this receptor.

New insight into the binding interaction of hydroxylated carbon nanotubes with bovine serum albumin

In order to understand the effects of carbon nanotubes on the structural stability of proteins, the ligand-binding ability, fibrillation, and chemical denaturation of bovine serum albumin in the presence of a multi-walled hydroxylated carbon nanotubes (HO-MWCNTs) was characterized by UV–vis, circular dichroism, fluorescence spectroscopy and molecule modeling methods at the molecular level. The experiment results indicated that the fluorescence intensity of BSA was decreased obviously in presence of HO-MWCNTs. The binding interaction of HO-MWCNTs with BSA led to the secondary structure changes of BSA. This interaction could not only affect the ligand-binding ability of BSA, but also change the rate of fibrillation and denaturation of BSA. This work gave us some important information about the structures and properties of protein induced by carbon nanotubes.

Metal ions optical sensing by semiconductor quantum dots

Colloidal semiconductor nanocrystals or quantum dots (QDs) have been facilitating the development of sensitive fluorescence sensors over the past decade, due to their unique photophysical properties, versatile surface chemistry and ligand binding ability, and the possibility of the encapsulation in different materials or attachment to different functional materials, while retaining their native luminescence property. The optical metal ion chemosensors with high sensitivity and selectivity have been developed due to the importance of the metal ions' fundamental roles, possessed in a wide range of biological processes and the aquatic environment. This review addresses the different sensing strategies with chemically modified QD hybrid structures for the sensing of metal ions in aqueous solution or an in vivo environment, and discusses the photophysical mechanisms in the different sensor systems while comparing their detecting/sensing selectivity. The perspectives for the future potential developments in QD based optical sensing for metal ions are discussed.

Analysis of the roles of mutations in thyroid hormone receptor-β by a bacterial biosensor system

Mutations in thyroid hormone receptors (TRs) often lead to metabolic and developmental disorders, but patients with these mutations are difficult to treat with existing thyromimetic drugs. In this study, we analyzed six clinically observed mutations in the ligand-binding domain of the human TRβ using an engineered bacterial hormone biosensor. Six agonist compounds, including triiodothyronine (T3), thyroxine (T4), 3,5,3'-triiodothyroacetic acid (Triac), GC-1, KB-141, and CO-23, and the antagonist NH-3 were examined for their ability to bind to each of the TRβ mutants. The results indicate that some mutations lead to the loss of ability to bind to native ligands, ranging from several fold to several hundred fold, while other mutations completely abolish the ability to bind to any ligand. Notably, the effect of each ligand on each TRβ mutant in this bacterial system is highly dependent on both the mutation and the ligand; some ligands were bound well by a wide variety of mutants, while other ligands lost their affinity for all but the WT receptor. This study demonstrates the ability of our bacterial system to differentiate agonist compounds from antagonist compounds and shows that one of the TRβ mutations leads to an unexpected increase in antagonist ability relative to other mutations. These results indicate that this bacterial sensor can be used to rapidly determine ligand-binding ability and character for clinically relevant TRβ mutants.