Interaction Of Agonists Research Articles

Differential regulation of muscarinic M1 receptors by orthosteric and allosteric ligands

BackgroundActivation of muscarinic M1 receptors is mediated via interaction of orthosteric agonists with the acetylcholine binding site or via interaction of allosteric agonists with different site(s) on the receptor. The focus of the present study was to determine if M1 receptors activated by allosteric agonists undergo the same regulatory fate as M1 receptors activated by orthosteric agonists.ResultsThe orthosteric agonists carbachol, oxotremorine-M and pilocarpine were compared to the allosteric agonists AC-42, AC-260584, N-desmethylclozapine and xanomeline. All ligands activated M1 receptors and stimulated interaction of the receptors with β-arrestin-1. All ligands reduced cell surface binding and induced the loss of total receptor binding. Receptor internalization was blocked by treatment with hypertonic sucrose indicating that all ligands induced formation of clathrin coated vesicles. However, internalized receptors recycled to the cell surface following removal of orthosteric, but not allosteric agonists. Whereas all ligands induced loss of cell surface receptor binding, no intracellular vesicles could be observed after treatment with AC-260584 or xanomeline. Brief stimulation of M1 receptors with AC-260584 or xanomeline resulted in persistent activation of M1 receptors, suggesting that continual receptor signaling might impede or delay receptor endocytosis into intracellular vesicles.ConclusionThese results indicate that allosteric agonists differ from orthosteric ligands and among each other in their ability to induce different regulatory pathways. Thus, signaling and regulatory pathways induced by different allosteric ligands are ligand specific.

Membrane promotes tBID interaction with BCLXL

Two important questions on the molecular mechanism of the B cell CLL/lymphoma 2 (BCL2) proteins involve the interaction network between pro- and antiapoptotic members and the role of their translocation to the mitochondrial membrane during apoptosis. We used fluorescence correlation spectroscopy to quantify the molecular interactions of BH3-interacting domain death agonist (BID) and its truncated form tBID with the B cell lymphoma extra-large protein truncated at the C terminus (BCL(XL)DeltaCt) in solution and in membranes, and we found that (i) only the active form tBID binds to BCL(XL)DeltaCt and (ii) that the membrane strongly promotes binding between them. Particularly, a BH3 peptide from BID disrupts the tBID-BCL(XL) complex in solution, but only partially in lipid bilayers. These data indicate that tBID-BCL(XL) interactions in solution and lipid membranes are distinct, and they support a model in which BCL(XL) inhibition of tBID takes place predominantly at the membrane. Our findings imply an active role of the membrane in modulating the interactions between BCL2 proteins that has so far been underestimated.

The Drosophila G protein‐coupled receptor, Methuselah, exhibits a promiscuous response to peptides

Methuselah (Mth) is a G protein-coupled receptor (GPCR) associated with longevity in Drosophila melanogaster. Previously, Stunted (Sun) was identified as a peptide agonist of Mth. Here, we identify two additional activators of Mth signaling: Drosophila Sex Peptide (SP) and a novel peptide (Serendipitous Peptide Activator of Mth, SPAM). Minimal functional sequences and key residues were identified from Sun and SPAM by studying truncation and alanine-scanning mutations. These peptide agonists share little sequence homology and illustrate the promiscuity of Mth for activation. mth mutants exhibit no defects in behaviors controlled by SP, casting doubt on the biological significance of Mth activation by any of these agonists, and illustrating the difficulty in applying in vitro studies to their relevance in vivo. Future studies of Mth ligands will help further our understanding of the functional interaction of agonists and GPCRs.

3H]Epibatidine Photolabels Non-equivalent Amino Acids in the Agonist Binding Site of Torpedo and α4β2 Nicotinic Acetylcholine Receptors

Nicotinic acetylcholine receptor (nAChR) agonists, such as epibatidine and its molecular derivatives, are potential therapeutic agents for a variety of neurological disorders. In order to identify determinants for subtype-selective agonist binding, it is important to determine whether an agonist binds in a common orientation in different nAChR subtypes. To compare the mode of binding of epibatidine in a muscle and a neuronal nAChR, we photolabeled Torpedo alpha(2)betagammadelta and expressed human alpha4beta2 nAChRs with [(3)H]epibatidine and identified by Edman degradation the photolabeled amino acids. Irradiation at 254 nm resulted in photolabeling of alphaTyr(198) in agonist binding site Segment C of the principal (+) face in both alpha subunits and of gammaLeu(109) and gammaTyr(117) in Segment E of the complementary (-) face, with no labeling detected in the delta subunit. For affinity-purified alpha4beta2 nAChRs, [(3)H]epibatidine photolabeled alpha4Tyr(195) (equivalent to Torpedo alphaTyr(190)) in Segment C as well as beta2Val(111) and beta2Ser(113) in Segment E (equivalent to Torpedo gammaLeu(109) and gammaTyr(111), respectively). Consideration of the location of the photolabeled amino acids in homology models of the nAChRs based upon the acetylcholine-binding protein structure and the results of ligand docking simulations suggests that epibatidine binds in a single preferred orientation within the alpha-gamma transmitter binding site, whereas it binds in two distinct orientations in the alpha4beta2 nAChR.

Structural determinants for interaction of partial agonists with acetylcholine binding protein and neuronal α7 nicotinic acetylcholine receptor

The pentameric acetylcholine-binding protein (AChBP) is a soluble surrogate of the ligand binding domain of nicotinic acetylcholine receptors. Agonists bind within a nest of aromatic side chains contributed by loops C and F on opposing faces of each subunit interface. Crystal structures of Aplysia AChBP bound with the agonist anabaseine, two partial agonists selectively activating the alpha7 receptor, 3-(2,4-dimethoxybenzylidene)-anabaseine and its 4-hydroxy metabolite, and an indole-containing partial agonist, tropisetron, were solved at 2.7-1.75 A resolution. All structures identify the Trp 147 carbonyl oxygen as the hydrogen bond acceptor for the agonist-protonated nitrogen. In the partial agonist complexes, the benzylidene and indole substituent positions, dictated by tight interactions with loop F, preclude loop C from adopting the closed conformation seen for full agonists. Fluctuation in loop C position and duality in ligand binding orientations suggest molecular bases for partial agonism at full-length receptors. This study, while pointing to loop F as a major determinant of receptor subtype selectivity, also identifies a new template region for designing alpha7-selective partial agonists to treat cognitive deficits in mental and neurodegenerative disorders.

Nicotinic Agonist Binding Site Mapped by Methionine- and Tyrosine-Scanning Coupled with Azidochloropyridinyl Photoaffinity Labeling

Agonists activating nicotinic acetylcholine receptors (nAChR) include potential therapeutic agents and also toxicants such as epibatidine and neonicotinoid insecticides with a chloropyridinyl substituent. Nicotinic agonist interactions with mollusk (Aplysia californica) acetylcholine binding protein, a soluble surrogate of the nAChR extracellular domain, are precisely defined by scanning with 17 methionine and tyrosine mutants within the binding site by photoaffinity labeling with 5-azido-6-chloropyridin-3-yl probes that have similar affinities to their nonazido counterparts. Methionine and tyrosine are the only residues found derivatized, and their reactivity exquisitely depends on the direction of the azido moiety and its apposition to the reactive amino acid side chains.

Improvement of the Closed Cranial Window Model in Rats by Intracarotid Infusion of Signalling Molecules Implicated in Migraine

Intravital microscopy on a closed cranial window allows one to measure change in the diameter of cranial blood vessels after intravenous (i.v.) administration of pharmacodynamic substances. Putative targets being pursued in migraine are large vasodilating peptide molecules such as calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase polypeptide (PACAP)-38. High i.v. doses are required to study their craniovascular pharmacology. Unfortunately, this leads to a drop in blood pressure (BP) that subsequently causes blood vessels to dilate by autoregulation. Hence it is difficult to decipher what effect is caused by direct receptor agonist interaction or contributed by autoregulation. In the present study we infused substances with an ingenious indwelling catheter in the common carotid artery in rats. Intracarotidly seven-, 12- and 17-fold lower doses of CGRP, PACAP-38 and capsaicin were required, respectively, compared with i.v. infusion to induce the same dilation in dural artery. Dilating intracarotid (i.c.) doses caused no or a minimal fall in BP, whereas equi-responsive i.v. doses caused a marked BP reduction. The CGRP blocking potential of olcegepant was amplified by > 20 times on i.c. infusion. Pial artery responses to CGRP did not change with i.c. infusion, demonstrating that dilations after i.v. CGRP are mediated by autoregulation rather than through specific receptors. We applied CGRP topically, which induced concentration-dependent dural vasodilation, but no effect on pial artery or on BP. In conclusion, this new approach offers an improvement of the existing model by allowing more accurate assessment of effects of pharmaca on the cranial vasculature without inducing significant systemic effects.

Molecular Modeling of Human Pentameric α7 Neuronal Nicotinic Acetylcholine Receptor and Its Interaction with its Agonist and Competitive Antagonist

The nicotinic Acetylcholine Receptor (nAChR) is the major class of neurotransmitter receptors that is involved in many neurodegenerative conditions such as schizophrenia, Alzheimer's and Parkinson's diseases. The N-terminal region or Ligand Binding Domain (LBD) of nAChR is located at pre- and post-synaptic nervous system, which mediates synaptic transmission. nAChR acts as the drug target for agonist and competitive antagonist molecules that modulate signal transmission at the nerve terminals. Based on Acetylcholine Binding Protein (AChBP) from Lymnea stagnalis as the structural template, the homology modeling approach was carried out to build three dimensional model of the N-terminal region of human α7nAChR. This theoretical model is an assembly of five α7 subunits with 5 fold axis symmetry, constituting a channel, with the binding pocket present at the interface region of the subunits. α-neurotoxin is a potent nAChR competitive antagonist that readily blocks the channel resulting in paralysis. The molecular interaction of α-Bungarotoxin, a long chain α-neurotoxin from (Bungarus multicinctus) and human α7nAChR was studied. Agonists such as acetylcholine, nicotine, which are used in a diverse array of biological activities, such as enhancements of cognitive performances, were also docked with the theoretical model of human α7nAChR. These docked complexes were analyzed further for identifying the crucial residues involved in interaction. These results provide the details of interaction of agonists and competitive antagonists with three dimensional model of the N-terminal region of human α7nAChR and thereby point to the design of novel lead compounds.

Evidence for Allosteric Interactions of Antagonist Binding to the Smoothened Receptor

The Smoothened receptor (Smo) mediates hedgehog (Hh) signaling critical for development, cell growth, and migration, as well as stem cell maintenance. Aberrant Hh signaling pathway activation has been implicated in a variety of cancers, and small-molecule antagonists of Smo have entered human clinical trials for the treatment of cancer. Here, we report the biochemical characterization of allosteric interactions of agonists and antagonists for Smo. Binding of two radioligands, [(3)H]3-chloro-N-[trans-4-(methylamino)cyclohexyl]-N-{[3-(4-pyridinyl)-phenyl]methyl}-1-benzothiophene-2-carboxamide (SAG-1.3) (agonist) and [(3)H]cyclopamine (antagonist), was characterized using human Smo expressed in human embryonic kidney 293F membranes. We observed full displacement of [(3)H]cyclopamine by all Smo agonist and antagonist ligands examined. N-[(1E)-(3,5-Dimethyl-1-phenyl-1H-pyrazol-4-yl)methylidene]-4-(phenylmethyl)-1-piperazinamine (SANT-1), an antagonist, did not fully inhibit the binding of [(3)H]SAG-1.3. In a functional cell-based beta-lactamase reporter gene assay, SANT-1 and N-[3-(1H-benzimidazol-2-yl)-4-chlorophenyl]-3,4,5-tris(ethyloxy)-benzamide (SANT-2) fully inhibited 3-chloro-4,7-difluoro-N-[trans-4-(methylamino)cyclohexyl]-N-{[3-(4-pyridinyl)phenyl]methyl}-1-benzothiophene-2-carboxamide (SAG-1.5)-induced Hh pathway activation. Detailed "Schild-type" radioligand binding analysis with [(3)H]SAG-1.3 revealed that two structurally distinct Smoothened receptor antagonists, SANT-1 and SANT-2, bound in a manner consistent with that of allosteric modulation. Our mechanism of action characterization of radioligand binding to Smo combined with functional data provides a better understanding of small-molecule interactions with Smo and their influence on the Hh pathway.

Modelling of α1‐adrenoceptor‐mediated temporal dynamics of inotropic response in rat heart to assess ligand binding and signal transduction parameters

In order to use the transient response to an antagonist (prazosin) to evaluate properties of agonist interactions with the alpha(1)-adrenoceptor system, an integrative mechanistic model of cardiac uptake of prazosin and its competitive interaction with phenylephrine at the receptor site was developed. Based on the operational model of agonism, the aim was to evaluate both the receptor binding and signal transduction process as determinants of the inotropic effect of phenylephrine. In Langendorff-perfused rat hearts, prazosin outflow concentration and left ventricular developed pressure were measured, first in the presence of 12.3 micromol x L(-1) phenylephrine following a 1 min infusion of 1.27 nmol [(3)H]-prazosin, and second, when after 30 min the phenylephrine concentration in perfusate was reduced to 6.1 micromol x L(-1), the 1 min infusion of 1.27 nmol [(3)H]-prazosin was repeated. The kinetic model accounted for cardiac uptake and receptor binding kinetics of prazosin (dissociation constant, mean +/- SD: 0.057 +/- 0.012 nmol.L(-1)), assuming that the competitive displacement of phenylephrine (dissociation constant: 101 +/- 13 nmol x L(-1)) reduced the receptor occupation by the agonist and, consequently, contractility. This competitive binding process appeared to be the rate-determining step in response generation. The relationship between receptor occupancy and inotropic response was described by an efficacy parameter (tau, ratio of receptor density and coupling efficiency) of 4.9. Mechanistic pharmacodynamic modelling of the kinetics of antagonism by prazosin allows quantitative assessment of the alpha(1)-adrenoceptor system both at the receptor and post-receptor levels.

Induction of supernumerary larval moulting in the tobacco hornworm Manduca sexta: interaction of bisacylhydrazine ecdysteroid agonists with endogenous Juvenile Hormone

Abstract When given in a critical dietary dose range, the insecticidal bisacylhydrazine ecdysteroid agonists RH‐5849 or tebufenozide (RH‐5992) cause fifth stage Manduca sexta (L.) larvae to moult to a supernumerary sixth‐stage giant larva. The effect is dependent on exposure to the chemicals immediately after the previous ecdysis. Previous removal of the corpora allata does not interfere with the induction of premature moulting by RH‐5849 but completely prevents the formation of supernumerary larvae. The juvenilizing effect is therefore due to the interaction of the moult‐promoting effect of the ecdysteroid agonists with the high titre of endogenous Juvenile Hormone that is present just after ecdysis to the fifth stage in this insect. The ecdysteroid agonists themselves appear to have no intrinsic Juvenile Hormone‐agonist properties. Sixth‐stage larvae resulting from exposure to critical dietary concentrations of RH‐5849 are morphologically completely larval in character. When transferred to diet without the ecdysteroid agonist, they feed normally and gain weight, growing much larger than control fifth stage insects. At the end of the supernumerary stage, they cease to feed, wander in the usual way, and form a normal pupal cuticle but then die as pharate pupae without shedding the sixth‐stage larval cuticle.

Role of TLR Agonist in Allergic Reactions to Drugs

RATIONALE: Lymphocyte transformation tests (LTT) is currently the only in vitro test available for diagnosing non-immediate allergic reactions (NIR) to drugs despite its low sensitivity. Dendritic cells (DC) have been used by our group to improve LTT sensitivity although it is still not optimal with some drugs probably because DC do not achieve a complete maturation. In these cases, a concomitant stimulation by TLR similar to the one that takes place in viral infections may contribute to a complete DC maturation and therefore a higher LTT. The aim of this work was to study how the interaction of drugs and agonist with TLR of DC induce changes in DC maturation and lymphocyte proliferation. METHODS: DC maturation was analyzed by flow cytometry and T cell proliferation to the drugs by LTT in presence or absence of TLR-7/8 agonist in subjects with a confirmed maculopapular exanthema (MPE) induced either by drugs or by virus and in healthy controls. RESULTS: Data showed an increase of DC maturational markers (HLA-DR, CD80 and CD86) compared to basal conditions in patients with MPE induced by drugs or viral infection. LTT was only positive (SI > 3) to the drug responsible of the reaction and when TLR agonist was present in the culture. In healthy controls no DC maturation was observed and LTT were negative. CONCLUSIONS: The presence of virus epitopes that interact with TLR from DC may increase LTT sensitivity in the evaluation of allergic reactions to drugs that occurred concomitantly to a viral infection.

Agonist and Antagonist Interactions in Beta Adrenergic Receptors

G-protein coupled receptors (GPCRs) are a large family of integral membrane proteins involved in signal transduction pathways, making them appealing drug targets for a wide spectrum of diseases. The recently solved X-ray structures of beta1 (B1AR) and beta2 (B2AR) adrenergic receptors bound to inverse agonists/antagonists open up a large field of potential investigations to understand the binding modes and mechanisms of activation of GPCRs.To investigate their structural and dynamic properties under pseudo in vivo conditions, we performed extensive molecular dynamics simulations (in an explicit membrane) of adrenergic receptors in complex with partial inverse agonists and agonists as well as in their apoform. To this end, we applied MD-based enhanced sampling techniques (steered MD, metadynamics, …) to describe ligand binding and to elucidate the process of ligand entrance and release.In this contribution, we rationalize the differences in binding mode between B1AR and B2AR for both agonists and antagonists (focusing on a limited set of key residues surrounding the binding pocket that are different between B1AR and B2AR). We also discuss main structural changes upon agonist/antagonist binding also in comparison with the most thoroughly studied GPCR, rhodopsin.

Dietary enrichment with wild blueberries ( Vaccinium angustifolium) affects the vascular reactivity in the aorta of young spontaneously hypertensive rats

We have previously reported on the positive effects of wild blueberries on arterial contractile response to α 1 adrenergic stimuli and on endothelium-mediated vasorelaxation. Our present study was designed to evaluate the effects of the dietary enrichment with wild blueberries on aortic function and reactivity in the developmental phase of essential hypertension in spontaneously hypertensive rats (SHR). We investigated the possible influence blueberries may have on the acetylcholine (Ach)-induced endothelium-dependent vasorelaxation and phenylephrine-induced vasoconstriction in young SHRs, as well as the contribution of the nitric oxide (NO) synthase and cyclooxygenase (COX) pathways in each of the above responses in an animal model with dysfunctional endothelium. Vascular ring studies were conducted in 3-mm isolated rat aortic ring preparations to investigate vasoconstriction induced by l-Phenylephrine (Phe, 10 −8 to 3×10 −6M) and vasorelaxation induced by acetylcholine (Ach, 10 −9 to 3×10 −6M). The major findings of our study were that in Phe-induced vasoconstriction, SHR-BB aortas relaxed to a greater degree in comparison to controls when mefenamic acid (MFA) was present and that the incubation with this COX inhibitor failed to restore — and in fact decreased — the maximum vasodilator response to Ach, in comparison to controls. Our vessel reactivity index ( pD 2) observations indicate that blueberries appear to modulate cell membrane–agonist (Ach) interactions primarily in response to Ach in the young SHR model, but not to the α 1 adrenoreceptor agonist. Incorporating wild blueberries in the diet seems to affect the endothelium-dependent vasorelaxation by modulating alternative metabolic pathway(s) (such as affecting the production/activity of COX-derived products) in the young SHR aorta.

Antinociceptive interactions of mu- and kappa-opioid agonists in the colorectal distension assay in rats

Interactions of opioid agonists, fentanyl and oxymorphone (mu-selective) and spiradoline and enadoline (kappa-selective), were examined for additive, sub-additive, or supra-additive antinociception in the colorectal distension (CRD) assay. Single-dose values (mg/kg, 0.006–0.016 for fentanyl, 0.25–1.26 for spiradoline, etc.) were summed to formulate theoretical additive-dose plots for comparison with actual combined-dose effects. Combined fentanyl and spiradoline yielded additive (low-dose levels) or supra-additive (high-dose levels) effects. Single and combined doses of fentanyl (0.012 mg/kg) and spiradoline (0.3 mg/kg) were tested after pretreatment with saline, beta-funaltrexamine (b-FNA, mu-selective antagonist), or nor-binaltorphimine (n-BNI, kappa-selective antagonist). Supra-additive effects of combined agonists were attenuated by either antagonist (greater with n-BNI). But paradoxical patterns of antagonism of single-dose effects occurred: the fentanyl antinociception was not antagonized by b-FNA, whereas the spiradoline antinociception was. The results indicate complex interactions of agonists in this visceral pain model and potential for combined agonists to improve pain relief with decreased side effects.

Establishment of Social Status without Individual Discrimination in the Cricket

Agonistic behavior in crickets was investigated to understand socially adaptive behavior, which assists with the understanding of the design of an artificial autonomous system in a social organization. Agonistic behavior between male crickets is released by the perception of cuticular substances of conspecific males. The degree of aggressiveness in crickets escalates from antennal fencing to tactical contact until one male quits fighting, at which time social status is established. The question of whether crickets are able to recognize one another to establish social status in an agonist interaction is worthy of pursuit. However, it would be difficult to conduct an experiment to explore this issue while using many individuals. Hence, we examined the social organization among male crickets using a two-step approach: (i) an experiment involving a simulated cricket behavior model and (ii) an experiment involving a behavior experiment using real animals. Our results suggest that crickets establish social status without recognition of their opponents.

Molecular Basis for the Selective Interaction of Synthetic Agonists with the Human Histamine H1-Receptor Compared with the Guinea Pig H1-Receptor

Previous studies revealed that phenylhistamines and histaprodifens possess higher potency and affinity at guinea pig histamine H(1)-receptor (gpH(1)R) than at human histamine H(1)-receptor (hH(1)R). However, we recently identified an imidazolylpropylguanidine [N(1)-(3-cyclohexylbutanoyl)-N(2)-[3-(1H-imidazol-4-yl)-propyl]guanidine (UR-AK57)] with higher potency and efficacy at hH(1)R compared with gpH(1)R. The aim of this study was to reveal the molecular basis for the species differences of synthetic ligands. We studied 11 novel phenylhistamines and phenoprodifens. H(1)R species isoforms were expressed in Sf9 insect cells, and [(3)H]mepyramine competition binding and GTPase assays were performed. We identified bulky phenylhistamines with higher potency and affinity at hH(1)R compared with gpH(1)R. Molecular dynamics simulations of ligand-H(1)R interactions revealed four potential binding modes for phenylhistamines possessing an additional histamine moiety; the terminal histamine moiety showed a high flexibility in the binding pocket. There are striking similarities in ligand properties in bulky phenylhistamines and UR-AK57. Comparison of bulky phenylhistamine binding mode with binding mode of UR-AK57 suggests that only one of these four binding modes should be established. The higher potency is explained by more effective van der Waals interaction of the compounds with Asn(2.61) (hH(1)R) relative to Ser(2.61) (gpH(1)R). In addition, two stable binding modes for phenoprodifens with different orientations in the binding-pocket were identified. Depending on phenoprodifen orientation, the highly conserved Trp(6.48), part of the toggle switch involved in receptor activation, was found in an inactive or active conformation, respectively. We identified the first phenylhistamines with higher potency at hH(1)R than at gpH(1)R and obtained insight into the binding mode of bulky phenylhistamines and imidazolylpropylguanidines.

Overview of Receptor Interactions of Agonists and Antagonists

Historically, the earliest methods used to quantitatively measure the fundamental properties of drugs (namely affinity and efficacy) employed isolated tissues, and it is in this realm that the null methods used to define "receptor pharmacology" were described. This unit describes these methods and their use to specifically classify agonists (through potency ratios and determination of relative affinities and efficacies) and antagonists (through analysis of surmountable and insurmountable antagonism) to yield estimates of potency. Different drugs can yield different behaviors in various tissues, so this unit is centered on a flow diagram to indicate the type of analysis appropriate for the behavior observed. For example, some agonists may be full agonists in some tissues and partial agonists in others, while some antagonists may demonstrate surmountable simple competitive antagonism in some tissues and insurmountable non-competitive antagonism in others. Methods exist for determination of affinity and efficacy for all of these behaviors, and these are delineated in this unit.

Purification and crystallization of a non-GluR2 AMPA-receptor ligand-binding domain: a case of cryo-incompatibility addressed by room-temperature data collection

Glutamate is the major excitatory neurotransmitter in the brain. Among the cognate ionotropic glutamate receptors, the subfamily selective for AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) is responsible for most fast excitatory synaptic signaling and plays key roles in synaptic plasticity. AMPA receptors (AMPA-Rs) have also been implicated in a number of neurological disorders. To investigate subunit-specific differences in the ligand binding and activation of AMPA-Rs, the GluR4 AMPA-R ligand-binding domain (LBD) was crystallized in complex with full and partial agonists. This is the first non-GluR2 AMPA-R LBD available for structural analysis. Standard cryoprotection protocols yielded high-resolution diffraction from flash-cooled crystals of the complex with the full agonist glutamate. However, for cocrystals with the partial agonist kainate, systematic screening and optimization of cryoprotection conditions yielded at best mosaic, weak diffraction at 100 K. In contrast, room-temperature data collection from capillary-mounted kainate cocrystals exhibited reproducible diffraction to better than 3 A resolution. Together, these crystals lay the foundation for a structural comparison of LBD-agonist interactions in distinct AMPA-R subunits.

Correction to “Molecular Interaction of a Potent Nonpeptide Agonist with the Chemokine Receptor CCR8”

Correction to “Molecular Interaction of a Potent Nonpeptide Agonist with the Chemokine Receptor CCR8”