Ligand Binding Activity Research Articles

Investigating GIPR (Ant)Agonism: A Structural Analysis of GIP and Its Receptor

The glucose-dependent insulinotropic polypeptide (GIP) is a 42-residue metabolic hormone that is actively being targeted for its regulatory role of glycemia and energy balance. Rational design of ligands, however, has been tedious with no structural data of the GIP receptor available. This study investigates structure and function of the GIP receptor (GIPR), using a homology model based on the GLP-1 receptor. Molecular dynamics combined with in vitro mutational data were used to pinpoint residues that play a role in ligand binding and/or receptor activation. Significant differences in binding mode were identified for the naturally occurring agonists GIP(1-30)NH2 and GIP(1-42) compared to high potency antagonists GIP(3-30)NH2 and GIP(5-30)NH2. Residues R1832.60, R1902.67 and R3005.40 are shown to play a key role in the activation of the GIPR and evidence suggests that a disruption of the K293ECL2 – E362ECL3 salt bridge by GIPR antagonists strongly reduces GIPR activation. These findings improve the basis for rational design of ligands targeting the GIPR.

The Glycosphingolipid GM3 Modulates Conformational Dynamics of the Glucagon Receptor

The extracellular domain (ECD) of class B1 G-protein-coupled receptors (GPCRs) plays a central role in signal transduction and is uniquely positioned to sense both the extracellular and membrane environments. Although recent studies suggest a role for membrane lipids in the modulation of class A and class F GPCR signaling properties, little is known about the effect of lipids on class B1 receptors. In this study, we employed multiscale molecular dynamics simulations to access the dynamics of the glucagon receptor (GCGR) ECD in the presence of native-like membrane bilayers. Simulations showed that the ECD could move about a hinge region formed by residues Q122–E126 to adopt both closed and open conformations relative to the transmembrane domain. ECD movements were modulated by binding of the glycosphingolipid GM3. These large-scale fluctuations in ECD conformation may affect the ligand binding and receptor activation properties. We also identify a unique phosphatidylinositol (4,5)-bisphosphate (PIP2) interaction profile near intracellular loop (ICL) 2/TM3 at the G-protein-coupling interface, suggesting a mechanism of engaging G-proteins that may have a distinct dependence on PIP2 compared with class A GPCRs. Given the structural conservation of class B1 GPCRs, the modulatory effects of GM3 and PIP2 on GCGR may be conserved across these receptors, offering new insights into potential therapeutic targeting.

Comparative Ligandomic Analysis of Human Lung Epithelial Cells Exposed to PM2.5

ObjectiveTo investigate whether exposure to particulate matter of diameter equal to or less than 2.5 μm (PM2.5) alters the response of lung epithelial cells to extrinsic regulation by globally profiling cell surface ligands and quantifying their binding activity. MethodsHuman A549 lung epithelial cells (LECs) were treated with or without PM2.5. Ligandomic profiling was applied to these cells for the global identification of LEC-binding ligands with simultaneous quantification of binding activity. Quantitative comparisons of the entire ligandome profiles systematically identified ligands with increased or decreased binding to PM2.5-treated LECs. ResultsWe found 143 ligands with increased binding to PM2.5-treated LECs and 404 ligands with decreased binding. Many other ligands showed no change in binding activity. For example, apolipoprotein E (ApoE), Notch2, and growth arrest-specific 6 (Gas6) represent ligands with increased, decreased, or unchanged binding activity, respectively. Both ApoE and Gas6 are phagocytosis ligands, suggesting that phagocytic receptors on LECs after stimulation with PM2.5 were differentially upregulated by PM2.5. ConclusionThese results suggest that the newly-developed ligandomics is a valuable approach to globally profile the response of LECs to PM2.5 in terms of regulating the expression of cell surface receptors, as quantified by ligand binding activity. This quantitative ligandome profiling will provide indepth understanding of the LEC molecular response on the cell surface to particulate matter air pollution.

Intracellular delivery of nanoparticles fabricated from monoclonal and polyclonal antibodies against influenza A and hepatitis B virus antigens

Specific antibodies (AB) may serve as molecular tools for both targeted, etiotropic and immunomodulation therapy of the infectious and oncological diseases. Despite their ability to bind with extracellular virions and isolated viral antigens AB may not pass through host cell membranes to inhibit intracellular infectious agents. Nanoparticles (NP) were fabricated from polyclonal and monoclonal AB against the influenza A structural and non-structural proteins as well as against the hepatitis B virus surface antigen (HBsAg). ELISA and immunofluorescent analysis revealed the ligand-binding activity of the AB NP comparable with the properties of the original AB. Fluorescent microscopy and quantitation showed efficient cellular uptake of the labeled AB NP and their degradation in 5 days posttreatment. Intracellular AB NP induced interferon (IFN) gene expression but not interleukin (IL) 4 and IL10 transcription. The cytokines mediated immunomodulation potential of the protein NP.

Long-term systemic administration of kynurenic acid brain region specifically elevates the abundance of functional CB1 receptors in rats

Kynurenic acid (KYNA) is one of the most significant metabolite of the kynurenine pathway both in terms of functional and potential therapeutic value. It is an N-methyl-D-aspartate (NMDA) receptor antagonist, but it can also activate the G-protein coupled receptor 35 (GPR35), which shares several structural and functional properties with cannabinoid receptors. Previously our group demonstrated that systemic chronic KYNA treatment altered opioid receptor G-protein activity. Opioid receptors also overlap in many features with cannabinoid receptors. Thus, our aim was to examine the direct in vitro and systemic, chronic in vivo effect of KYNA on type 1 cannabinoid receptor (CB1R) binding and G-protein activity.Based on competition and [35S]GTPγS G-protein binding assays in rat brain, KYNA alone did not show significant binding towards the CB1R, nor did it alter CB1R ligand binding and agonist activity in vitro. When rats were chronically treated with KYNA (single daily, i.p., 128 mg/kg for 9 days), the KYNA plasma and cerebrospinal fluid levels significantly increased compared to vehicle treated group. Furthermore, in G-protein binding assays, in the whole brain the amount of G-proteins in basal and in maximum activity coupled to the CB1R also increased due to the treatment. At the same time, the overall stimulatory properties of the receptor remained unaltered in vehicle and KYNA treated samples. Similar observations were made in rat hippocampus, but not in the cortex and brainstem. In saturation binding assays the density of CB1Rs in rat whole brain and hippocampus were also significantly enhanced after the same treatment, without significantly affecting ligand binding affinity.Thus, KYNA indirectly and brain region specifically increases the abundance of functional CB1Rs, without modifying the overall binding and activity of the receptor. Supposedly, this can be a compensatory mechanism on the part of the endocannabinoid system induced by the long-term KYNA exposure.

Essential role of the C148–C227 disulphide bridge in the human 5-HT2A homodimeric receptor

The 5-HT2A receptor is a homodimeric G protein-coupled receptor implied in multiple diseases, including schizophrenia. Recently, its co-crystallisation with the antipsychotic drugs zotepine and risperidone has revealed the importance of its extracellular domains in its pharmacology. Previous studies have shown that the non-specific disruption of extracellular disulphide bridges in the 5-HT2A receptor decreases ligand binding and receptor activation. There is enough evidence to hypothesize that this decrease may be due to a reduction of the disulphide bridge that links transmembrane domain 3 (TM-3) and extracellular loop 2 (ECL-2) of the 5-HT2A receptor via cysteine 148 (C148) and C227.Thus, to study the influence of the C148–C227 disulphide bridge on 5-HT2A receptor pharmacology, we substituted C148 and C227 in the human 5-HT2A receptor (WT) with alanines, to obtain two single mutants (C148A and C227A) and a double mutant (C148A/C227A), and the resultant DNA constructs were used to generate four stable cell lines. These substitutions reduced the binding of the 5-HT2A receptor to [3H]lysergic acid diethylamide ([3H]LSD) and impeded the 5-HT2A receptor-mediated activation of phospholipase C (PLC). Furthermore, bioluminescence resonance energy transfer (BRET) and western blotting analysis revealed that these mutations did not alter the homodimeric nature of the 5-HT2A receptor. However, fluorescence microscopy showed that these mutations hindered receptor trafficking to the cell membrane.These results illustrate the importance of the disulphide bridge between TM-3 and ECL-2 in maintaining the correct 5-HT2A receptor conformation to allow ligand binding and migration of the homodimeric receptor to the cell membrane.

Rational development of a high-affinity secretin receptor antagonist

The secretin receptor is a prototypic class B GPCR with substantial and broad pharmacologic importance. The aim of this project was to develop a high affinity selective antagonist as a new and important pharmacologic tool and to aid stabilization of this receptor in an inactive conformation for ultimate structural characterization. Amino-terminal truncation of the natural 27-residue ligand reduced biological activity, but also markedly reduced binding affinity. This was rationally and experimentally overcome with lactam stabilization of helical structure and with replacement of residues with natural and unnatural amino acids. A key new step in this effort was the replacement of peptide residue Leu22 with L-cyclohexylalanine (Cha) to enhance potential hydrophobic interactions with receptor residues Leu31, Val34, and Phe92 that were predicted from molecular modeling. Alanine-replacement mutagenesis of these residues markedly affected ligand binding and biological activity. The optimal antagonist ligand, (Y10,c[E16,K20],I17,Cha22,R25)sec(6–27), exhibited high binding affinity (4 nM), similar to natural secretin, and exhibited no demonstrable biological activity to stimulate cAMP accumulation, intracellular calcium mobilization, or β-arrestin-2 translocation. It acts as an orthosteric competitive antagonist, predicted to bind within the peptide-binding groove in the receptor extracellular domain. The analogous peptide that was one residue longer, retaining Thr5, exhibited partial agonist activity, while further truncation of even a single residue (Phe6) reduced binding affinity. This sec(6–27)-based peptide will be an important new tool for pharmacological and structural studies.

Extracellular Redox Regulation of α7β Integrin-Mediated Cell Migration Is Signaled via a Dominant Thiol-Switch

While adhering to extracellular matrix (ECM) proteins, such as laminin-111, cells temporarily produce hydrogen peroxide at adhesion sites. To study the redox regulation of α7β1 integrin-mediated cell adhesion to laminin-111, a conserved cysteine pair within the α-subunit hinge region was replaced for alanines. The molecular and cellular effects were analyzed by electron and atomic force microscopy, impedance-based migration assays, flow cytometry and live cell imaging. This cysteine pair constitutes a thiol-switch, which redox-dependently governs the equilibrium between an extended and a bent integrin conformation with high and low ligand binding activity, respectively. Hydrogen peroxide oxidizes the cysteines to a disulfide bond, increases ligand binding and promotes cell migration toward laminin-111. Inversely, extracellular thioredoxin-1 reduces the disulfide, thereby decreasing laminin binding. Mutation of this cysteine pair into the non-oxidizable hinge-mutant shows molecular and cellular effects similar to the reduced wild-type integrin, but lacks redox regulation. This proves the existence of a dominant thiol-switch within the α subunit hinge of α7β1 integrin, which is sufficient to implement activity regulation by extracellular redox agents in a redox-regulatory circuit. Our data reveal a novel and physiologically relevant thiol-based regulatory mechanism of integrin-mediated cell-ECM interactions, which employs short-lived hydrogen peroxide and extracellular thioredoxin-1 as signaling mediators.

GSTP1 Inhibits LPS-Induced Inflammatory Response Through Regulating Autophagy in THP-1 Cells.

Glutathione S-transferase Pi (GSTP1) was originally identified as one of the cytosolic phase II detoxification enzymes and was also considered to function via its non-catalytic, ligand-binding activity. Autophagy is a self-protective mechanism of the cell to remove unnecessary or dysfunctional components, which plays a crucial role in balancing the beneficial and detrimental effects of immunity and inflammation. However, little is known about whether and how GSTP1 mediates autophagy via inhibiting LPS-induced inflammatory response. Here, we show that LPS-induced autophagy and autophagic flux blockade in THP-1 cells in a concentration- and time-dependent manner. Further, we found that the autophagy activation inhibited the activation of inflammatory signaling pathway and the release of inflammatory factors. However, inhibition of autophagy by 3-methyladenine or chloroquine significantly reduced the anti-inflammatory effect of GSTP1. In addition, our findings provide evidence that GSTP1 regulates autophagy through PI3K-Akt-mTOR pathway and inhibits LPS-induced inflammation. Overall, the current study provides an important reference for future applications of GSTP1 in the treatment of inflammatory diseases.

Benzofuran and coumarin derivatives from the root of Angelica dahurica and their PPAR-γ ligand-binding activity

A phytochemical investigation of the root of Angelica dahurica led to the isolation of benzofuran and coumarin derivatives. This is the first report of the isolation and identification of three furanocoumarin sulfates from A. dahurica root. The structures of a total of twelve undescribed compounds were determined by extensive spectroscopic analysis, including 2D NMR data, hydrolysis, and solvolysis, followed by either physicochemical and spectroscopic data or X-ray crystallographic analysis. The isolated compounds were evaluated for their PPAR-γ ligand-binding activity, and six compounds showed significant PPAR-γ ligand-binding activity. In particular, the undescribed benzofuran derivative, 3-[6,7-furano-9-hydroxy-4-(2″,3″-dihydroxy-3″-methylbutyloxy)]-phenyl propionic acid, exhibited the most potent PPAR-γ ligand-binding activity and accumulated intracellular lipid in 3T3-L1 cells.

Chemical Constituents of the Terrestrial Stems of Ephedra sinica and their PPAR-γ Ligand-Binding Activity

AbstractBioassay-guided fractionation of the MeOH extract of Ephedra sinica terrestrial stems, using a PPAR-γ ligand binding assay, resulted in the isolation of 10 compounds, including one new bisabolane-type sesquiterpenoid (10). The structure of the new compound was determined by extensive spectroscopic analysis, including two-dimensional (2D) NMR. Among the isolated compounds, the sitosterol derivatives (1 and 2), flavonoid glucoside (7), and the new sesquiterpenoid (10), showed significant PPAR-γ ligand-binding activity.

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.

Surface Plasmon Resonance as a Tool for Ligand Binding Investigation of Engineered GPR17 Receptor, a G Protein Coupled Receptor Involved in Myelination.

The aim of this study was to investigate the potential of surface plasmon resonance (SPR) spectroscopy for the measurement of real-time ligand-binding affinities and kinetic parameters for GPR17, a G protein-coupled receptor (GPCR) of major interest in medicinal chemistry as potential target in demyelinating diseases. The receptor was directly captured, in a single-step, from solubilized membrane extracts on the sensor chip through a covalently bound anti-6x-His-antibody and retained its ligand binding activity for over 24 h. Furthermore, our experimental setup made possible, after a mild regeneration step, to remove the bound receptor without damaging the antibody, and thus to reuse many times the same chip. Two engineered variants of GPR17, designed for crystallographic studies, were expressed in insect cells, extracted from crude membranes and analyzed for their binding with two high affinity ligands: the antagonist Cangrelor and the agonist Asinex 1. The calculated kinetic parameters and binding constants of ligands were in good agreement with those reported from activity assays and highlighted a possible functional role of the N-terminal residues of the receptor in ligand recognition and binding. Validation of SPR results was obtained by docking and molecular dynamics of GPR17-ligands interactions and by functional in vitro studies. The latter allowed us to confirm that Asinex 1 behaves as GPR17 receptor agonist, inhibits forskolin-stimulated adenylyl cyclase pathway and promotes oligodendrocyte precursor cell maturation and myelinating ability.

Direct Monitoring of GPCR Reconstitution and Ligand-Binding Activity by Plasmon Waveguide Resonance.

The study of G-protein-coupled receptor (GPCR ) mechanisms of activation and signaling often the isolation, purification, and reconstitution of GPCRs in model lipid membranes. GPCR reconstitution from a detergent-micelle system into model membranes is usually a laborious process whose success is tested after the whole process is over by rather indirect methods such as SDS-PAGE and western blotting or by biophysical approaches. Following that, protein activity is measured in yet a different experimental setup. Overall, the whole procedure is tedious, long, and often requires high quantities of material and the use of labeled proteins. Herein, a protocol is described to follow, in a single experimental setup, both GPCR reconstitution from detergent micelles into planar lipid bilayers and its ligand-binding activity using plasmon waveguide resonance. Alternatively, receptor/ligand interactions can also be investigated from cell membrane fragments overexpressing the receptor of interest, bypassing isolation and reconstitution procedures. The method is direct, sensitive, and does not rely on the use of any labeled material.

The use of consensus sequence information to engineer stability and activity in proteins.

The goal of protein design is to create proteins that are stable, soluble, and active. Here we focus on one approach to protein design in which sequence information is used to create a "consensus" sequence. Such consensus sequences comprise the most common residue at each position in a multiple sequence alignment (MSA). After describing some general ideas that relate MSA and consensus sequences and presenting a statistical thermodynamic framework that relates consensus and non-consensus sequences to stability, we detail the process of designing a consensus sequence and survey reports of consensus design and characterization from the literature. Many of these consensus proteins retain native biological activities including ligand binding and enzyme activity. Remarkably, in most cases the consensus protein shows significantly higher stability than extant versions of the protein, as measured by thermal or chemical denaturation, consistent with the statistical thermodynamic model. To understand this stability increase, we compare various features of consensus sequences with the extant MSA sequences from which they were derived. Consensus sequences show enrichment in charged residues (most notably glutamate and lysine) and depletion of uncharged polar residues (glutamine, serine, and asparagine). Surprisingly, a survey of stability changes resulting from point substitutions show little correlation with residue frequencies at the corresponding positions within the MSA, suggesting that the high stability of consensus proteins may result from interactions among residue pairs or higher-order clusters. Whatever the source, the large number of reported successes demonstrates that consensus design is a viable route to generating active and in many cases highly stabilized proteins.

Prediction of 3D Protein Structure Based on The Mutation of AKAP3 and PLOD3 Genes in The Case of Non-Obstructive Azoospermia.

BackgroundThe present study has been designed with the aim of evaluating A-kinase anchoring proteins 3 (AKAP3) and Procollagen-Lysine, 2-Oxoglutarate 5-Dioxygenase 3 (PLOD3) gene mutations and prediction of 3D protein structure for ligand binding activity in the cases of non-obstructive azoospermic male.Materials and MethodsClinically diagnosed cases of non-obstructive azoospermia (n=111) with age matched controls (n=42) were included in the present case-control study for genetics analysis and confirmation of diagnosis. The sample size was calculated using Epi info software version 6 with 90 power and 95% confidence interval. Genomic DNA was isolated from blood (2.0 ml) and a selected case was used for whole exome sequencing (WES) using Illumina Hiseq for identification of the genes. Bioinformatic tools were used for decode the amino acid sequence from biological database (www.ncbi.nlm.nih.gov/protein). 3D protein structure of AKAP3 and PLOD3 genes was predicted using I-TASSER server and binding energy was calculated by Ramachandran plot.ResultsPresent study revealed the mutation of AKAP3 gene, showing frameshift mutation at rs67512580 (ACT → -CT) and loss of adenine in homozygous condition, where, leucine changed into serine. Similarly, PLOD3 gene shows missense mutation in heterozygous condition due to loss of guanine in the sequence AGG→A-G and it is responsible for the change in post-translational event of amino acid where arginine change into lysine. 3D structure shows 8 and 4 pockets binding site in AKAP3 and PLOD3 gene encoded proteins with MTX respectively, but only one site bound to the receptor with less binding energy representing efficient model of protein structure.ConclusionThese genetic variations are responsible for alteration of translational events of amino acid sequences, leading to protein synthesis change following alteration in the predicted 3D structure and functions during spermiogen- esis, which might be a causative “risk” factor for male infertility.

Nanomechanics of the molecular complex between staphylococcal adhesin SpsD and elastin.

Staphylococcus pseudintermedius surface protein SpsD binds to extracellular matrix proteins to invade canine epithelial cells. Using single-molecule experiments, we show that SpsD engages in two modes of interaction with elastin that are tightly controlled by physical stress. Binding is weak (∼100 pN) at low tensile force (i.e. loading rate), but is dramatically enhanced (up to ∼1500 pN) by mechanical tension. Consistent with a "dock, lock, and latch" (DLL) mechanism, this force represents among the highest mechanical strengths known for a non-covalent biological interaction. The transition from weak to strong binding correlates with an increase in molecular stiffness but, surprisingly, with a decrease in molecular extension. This unanticipated mechanical behavior indicates that the adhesin is engaged in two distinct interaction mechanisms. Our results emphasize the crucial role of protein nanomechanics in the adhesion of staphylococci, and illustrate their wide diversity of force-dependent ligand-binding activities. These single-molecule mechanical experiments may contribute to the development of antiadhesion approaches to treat infections caused by S. pseudintermedius and other bacterial pathogens engaged in DLL interactions.

Evaluation of chemical cross-linkers for in-depth structural analysis of G protein-coupled receptors through cross-linking mass spectrometry

Chemical cross-linking would conceivably cause structural disruption of a protein, but few cross-linkers have been fully evaluated in this aspect. Furthermore, integral membrane proteins may differ from soluble proteins in the selection of suitable cross-linkers, which has never been investigated. In this study, we systematically evaluated the impact of five conventional cross-linkers targeting Lys, Asp and Glu, and two Arg-reactive cross-linkers on the structural and functional integrity of two G protein-coupled receptors (GPCRs). Perturbation of the receptor structure and ligand-binding activity was observed, depending on the receptor and cross-linking conditions. In particular, our study demonstrated that the concentrations of PDH and KArGO need to be fine-tuned in order to minimize the structural and functional disturbance of specific GPCRs. A set of amenable cross-linkers was selected to acquire the most comprehensive cross-link maps for two GPCRs. Our in-depth cross-linking mass spectrometry (CXMS) analysis has revealed dynamic features of structural regions in GPCRs that are not observable in the crystal structures. Thus, CXMS analysis of GPCRs using the expanded toolkit would facilitate structural modeling of uncharacterized receptors and gain new insights into receptor-ligand interactions.

BiAb Mediated Restoration of the Linkage between Dystroglycan and Laminin-211 as a Therapeutic Approach for α-Dystroglycanopathies.

Patients with α-dystroglycanopathies, a subgroup of rare congenital muscular dystrophies, present with a spectrum of clinical manifestations that includes muscular dystrophy as well as CNS and ocular abnormalities. Although patients with α-dystroglycanopathies are genetically heterogeneous, they share a common defect of aberrant post-translational glycosylation modification of the dystroglycan alpha-subunit, which renders it defective in binding to several extracellular ligands such as laminin-211 in skeletal muscles, agrin in neuromuscular junctions, neurexin in the CNS, and pikachurin in the eye, leading to various symptoms. The genetic heterogeneity associated with the development of α-dystroglycanopathies poses significant challenges to developing a generalized treatment to address the spectrum of genetic defects. Here, we propose the development of a bispecific antibody (biAb) that functions as a surrogate molecular linker to reconnect laminin-211 and the dystroglycan beta-subunit to ameliorate sarcolemmal fragility, a primary pathology in patients with α-dystroglycan-related muscular dystrophies. We show that the treatment of LARGEmyd-3J mice, an α-dystroglycanopathy model, with the biAb improved muscle function and protected muscles from exercise-induced damage. These results demonstrate the viability of a biAb that binds to laminin-211 and dystroglycan simultaneously as a potential treatment for patients with α-dystroglycanopathy.

QTY code designed thermostable and water-soluble chimeric chemokine receptors with tunable ligand affinity

Chemokine receptors are of great interest as they play a critical role in many immunological and pathological processes. The ability to study chemokine receptors in aqueous solution without detergent would be significant because natural receptors require detergents to become soluble. We previously reported using the QTY code to design detergent-free chemokine receptors. We here report the design of 2 detergent-free chimeric chemokine receptors that were experimentally unattainable in detergent solution. We designed chimeric receptors by switching the N terminus and 3 extracellular (EC) loops between different receptors. Specifically, we replaced the N terminus and 3 EC loops of CCR5QTY with the N terminus and 3 EC loops of CXCR4. The ligand for CXCR4; namely CXCL12, binds to the chimeric receptor CCR5QTY (7TM)-CXCR4 (N terminus+3 EC loops), but with lower affinity compared to CXCR4; the CCL5 ligand of CCR5 binds the chimeric receptor with ∼20× lower affinity. The chimeric design helps to elucidate the mechanism of native receptor-ligand interaction. We also show that all detergent-free QTY-designed chemokine receptors, expressed in Escherichia coli, bind to their respective chemokines with affinities in the nanomolar (nM) range, similar to the affinities of native receptors and SF9-produced QTY variants. These QTY-designed receptors exhibit remarkable thermostability in the presence of arginine and retain ligand-binding activity after heat treatment at 60 °C for 4 h and 24 h, and at 100 °C for 10 min. Our design approach enables affordable scale-up production of detergent-free QTY variant chemokine receptors with tunable functionality for various uses.