Production of a Human Histamine Receptor for NMR Spectroscopy in Aqueous Solutions.

G protein-coupled receptors (GPCRs) bind a broad array of extracellular molecules and transmit intracellular signals that initiate physiological responses. The signal transduction functions of GPCRs are inherently related to their structural plasticity, which can be experimentally observed by spectroscopic techniques. Nuclear magnetic resonance (NMR) spectroscopy in particular is an especially advantageous method to study the dynamic behavior of GPCRs. The success of NMR studies critically relies on the production of functional GPCRs containing stable-isotope labeled probes, which remains a challenging endeavor for most human GPCRs. We report a protocol for the production of the human histamine H1 receptor (H1R) in the methylotrophic yeast Pichia pastoris for NMR experiments. Systematic evaluation of multiple expression parameters resulted in a ten-fold increase in the yield of expressed H1R over initial efforts in defined media. The expressed receptor could be purified to homogeneity and was found to respond to the addition of known H1R ligands. Two-dimensional transverse relaxation-optimized spectroscopy (TROSY) NMR spectra of stable-isotope labeled H1R show well-dispersed and resolved signals consistent with a properly folded protein, and 19F-NMR data register a response of the protein to differences in efficacies of bound ligands.

High-throughput production and structural characterization of libraries of self-assembly lipidic cubic phase materials.

A protocol is presented for the high-throughput (HT) production of lyotropic liquid crystalline phases from libraries of lipids and lipid mixtures using standard liquid dispensing robotics, implementing methods that circumvent the problems traditionally associated with handling the highly viscous cubic phase. In addition, the ability to structurally characterize lipidic phases and assess functionality for membrane proteins contained within cubic phases, in a HT manner, is demonstrated. The techniques are combined and exemplified using the application of membrane protein crystallization within lipidic cubic phases.

Production of the stable human histamine H1 receptor in Pichia pastoris for structural determination.

G-protein coupled receptors (GPCRs) play essential roles in regulation of many physiological processes and are one of the major targets of pharmaceutical drugs. The 3D structure can provide important information for the understanding of GPCR function and the design of new drugs. However, the success of structure determination relies largely on the production of recombinant GPCRs, because the expression levels of GPCRs are very low in native tissues except rhodopsin. All non-rhodopsin GPCRs whose structures were determined so far were expressed in insect cells and the availability of other hosts was unknown. Recently, we succeeded to determine the structure of human histamine H(1) receptor (H(1)R) expressed in Pichia pastoris. Here, we report the expression and purification procedures of recombinant H(1)R used in the structural determination. The receptor was designed to possess a N-terminal 19-residue deletion and a replacement of the third cytoplasmic loop with T4-lysozyme. The receptor was verified to show similar binding activities with the receptor expressed in other hosts. The receptor was purified by the immobilized metal ion affinity chromatography and used for the crystallographic study that resulted in the successful structure determination.

Identification of zebrafish histamine H1, H2 and H3 receptors and effects of histaminergic ligands on behavior.

Neuronal histamine regulates several functions in the vertebrate brain. The zebrafish brain contains a widespread histaminergic system and H(3) receptor ligand binding has been reported. In this study we provide evidence for the existence of histamine H(1), H(2) and H(3) receptor genes in zebrafish. Single copies of putative histamine H(1), H(2) and H(3) receptors were identified and cloned from the zebrafish brain. Expression analysis suggested that they are expressed in the brain and a few other tissues. Widespread distribution of zebrafish H(2) receptor binding sites was detected with [(125)I]iodoaminopotentidine in brain sections. Zebrafish larvae were exposed to 1, 10 or 100 microM of the H(1) ligand pyrilamine, the H(2) ligand cimetidine and the H(3) ligands thioperamide and immepip for 5 days. Significant decreases in swimming distance were observed with the highest dose of all ligands, whereas cimetidine gave a significant decrease also with 1 and 10 microM doses. These results provide the first molecular biological evidence for the presence of histamine receptors in zebrafish. These histamine receptors resemble those of higher vertebrates and they provide a useful model for pharmacological and behavioral studies for characterizing the functions of histamine in more detail.

Large-scale overproduction, functional purification and ligand affinities of the His-tagged human histamine H1 receptor.

This report describes an efficient strategy for amplified functional purification of the human H1 receptor after heterologous expression in Sf9 cells. The cDNA encoding a C-terminally histidine-tagged (10xHis) human histamine H1 receptor was used to generate recombinant baculovirus in a Spodoptera frugiperda-derived cell line (IPLB-Sf9). As judged from its ligand affinity profile, functional receptor could be expressed at high levels (30-40 pmol per 10(6) cells). Rapid proteolysis in the cell culture led to limited fragmentation, without loss of ligand binding, but could be efficiently suppressed by including the protease inhibitor leupeptin during cell culture and all subsequent manipulations. Effective solubilization of functional receptor with optimal recovery and stability required the use of dodecylmaltoside as a detergent in the presence of a high concentration of NaCl and of a suitable inverse agonist. Efficient purification of solubilized receptor could be achieved by affinity chromatography over nickel(II) nitrilotriacetic acid resin. Functional membrane reconstitution of purified H1 receptor was accomplished in mixed soybean lipids (asolectin). The final proteoliposomic H1 receptor preparation has a purity greater than 90% on a protein basis and displays a ligand binding affinity profile very similar to the untagged receptor expressed in COS-7 cells. In conclusion, we are able to produce pharmacologically viable H1 receptor in a stable membrane environment allowing economic large-batch operation. This opens the way to detailed studies of structure-function relationships of this medically and biologically important receptor protein by 3D-crystallography, FT-IR spectroscopy and solid-state NMR spectroscopy.

Effect of histamine on phosphoinositide turnover and intracellular calcium in human ciliary muscle cells.

This report describes the effect of histamine on phospholipase C (PLC) activity and calcium mobilization in cultured human ciliary muscle cells. PLC activity was assessed by measuring the production of inositol phosphates and intracellular calcium mobilization was assessed by Fura 2 ratio fluorometry. The stimulation of PLC by histamine was concentration dependent with an EC50 of 0.96 microM. The H1 antagonist chlorpheniramine blocked the response with an IC50 of 0.53 microM. Calcium fluorometry experiments indicated a mean basal calcium concentration of 36 nM with a 10(-4) M histamine induced mean peak value of 1132 nM followed by a gradually declining plateau phase. EC50 and IC50 (chlorpheniramine) values from histamine induced peak calcium concentrations agreed with the PLC results. Pretreatment of the cells with the PLC inhibitor U73122 at 10(-6) M completely blocked histamine induced calcium mobilization. Removal of extracellular calcium eliminated the plateau phase but not the initial calcium peak indicating that both intra and extracellular calcium sources are required for a normal response. The calcium ATPase inhibitor thapsigargin caused depletion of intracellular calcium stores and prevented a subsequent normal calcium mobilization response to histamine. Ryanodine, a release inhibitor of certain intracellular calcium stores, had no effect on the histamine induced response. The results of these experiments indicate that histamine, via an H1 receptor, activated the PLC second messenger pathway, and caused a multi-phasic mobilization of both intracellular and extracellular calcium. The entry of the extracellular calcium was shown to be dependent upon release of calcium from a ryanodine insensitive intracellular store.

Design of an affinity matrix for purification of the histamine H1 receptor from guinea pig cerebellum.

H1 receptors from guinea pig cerebellum were solubilized using digitonin, and [125I]iodobolpyramine was used as a probe. [125I]Iodobolpyramine binding to this solubilized preparation occurred with a KD of 0.1 nM and a Bmax of 220 fmol/mg of protein and was inhibited by various H1 ligands with the expected potencies. Using a gel filtration procedure, a very sensitive radioassay was set up for detecting H1 activity in the solubilized preparation: 0.1 nM [125I]iodobolpyramine specific binding represented greater than 90% of total binding. Moreover, the synthesis is described of potent H1 antagonists that are mepyramine derivatives with an amino alkyl acylamido alkyl spacer arm. One of them, UCL 1057 (Ki = 0.5 nM), has been coupled to a Sepharose epoxy-activated resin. The resulting affinity matrix adsorbed selectively [125I]iodobolpyramine binding sites from the guinea pig cerebellum soluble preparation. In contrast, a Sepharose-glycine matrix was not able to adsorb these sites.

Biochemical characterization of histamine H1 receptors in bovine adrenal medulla.

Bovine adrenal medullary membranes display high affinity and saturable binding to [3H]mepyramine, a selective H1 antagonist, with Kd of 1.5 +/- 0.1 nM and Bmax of 694 +/- 12 fmol/mg protein. [3H]Azidobenzpyramine, an azidobenzamide derivative of mepyramine, was synthesized and used to photolabel the high affinity mepyramine binding sites. Following photolysis, a protein component with an approximate molecular weight of 53-58 kDa was shown to be covalently labeled, as judged by gel filtration and SDS/PAGE; labeling being greatly reduced in the presence of excess unlabeled mepyramine. These results indicate that bovine adrenal medulla expresses a large number of H1 receptors, which are pharmacologically and biochemically indistinguishable from the H1 receptor of many other tissues of various species.

Solubilization and characterization of the pyrilamine-binding protein from cultured smooth muscle cells.

The cultured smooth muscle cell line DDT1MF-2 expresses a large number (9.7 x 10(6) receptors/cell) of functional histamine H1-type receptors [J. Cell. Physiol. 134:367-375 1988]. Two different binding assays, gel filtration and polyethylene glycol precipitation, indicated that the [3H]pyrilamine binding activity was solubilized by 1% digitonin with binding characteristics similar to those of intact cells. The solubilized proteins were then purified by sequential gel filtration, chromatofocusing, and reverse phase high pressure liquid chromatography. The calculated molecular weight of this purified pyrilamine-binding protein was 38-40 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. [3H]Pyrilamine binding to these 38-40-kDa proteins indicated a single class of binding site with a Kd of 288 nM, which is equivalent to that of intact cells and digitonin-solubilized proteins. The computer analysis Scatfit also indicated that one molecule of [3H]pyrilamine bound to one molecule of purified protein. Furthermore, a polyclonal antibody raised against the purified protein recognized the 38-40-kDa band by Western blotting techniques, specifically bound to the cell surface of DDT1MF-2 cells, and inhibited [3H]pyrilamine binding to these cells in a dose-dependent manner. These data strongly suggest that the purified 38-40-kDa protein is part of an antagonist binding domain on the histamine H1 receptor on DDT1MF-2 cells.

Digitonin-solubilized histamine H1-receptors bind to polyethylenimine-treated glass-fibre filters.

The binding of [3H]mepyramine to histamine H1-receptors solublized from guinea-pig cerebellum by 1% digitonin could be assayed by adsorption of the receptor-bound [3H]ligand to glass-fibre filters pretreated with 0.3% polyethylenimine (PEI). Non-specific binding was higher than in parallel experiments in which the bound and free [3H]ligand was separated by gel-filtration on Sephadex G-25 columns, but the parameters characterizing the inhibition curves were otherwise similar. The PEI-treated filter method could also be used to assay [3H]-(+)-N-methyl-4-methyl-diphenhydramine ([3H]QMDP) binding to solubilized H1-receptors, but the level of non-specific binding was higher and was only satisfactorily defined by icotidine or temelastine. A particular utility of the PEI-treated filter assay will be in measurements of the kinetics of H1-receptor-ligand interactions.

Solubilization, characterization and partial purification of [3H]mepyramine-binding protein, a possible histamine H1 receptor, from rat liver membrane.

[3H]Mepyramine binding protein, a possible subtype of histamine H1 receptors, was solubilized from rat liver membrane with 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS) and Tween 60 as detergents and glycerol as an enhancer of solubilization. The optimal concentration of CHAPS was 10 mM and that of glycerol was 20% or more (v/v). The molecular weight of the [3H]mepyramine binding protein-detergent complex was determined to be 670K by Sepharose CL-4B gel filtration and 800K by sucrose density gradient sedimentation. By target size analysis, the molecular weights of both the membrane-bound and solubilized [3H]mepyramine binding protein were determined to be 162K. These values are similar to those of other well-characterized H1-receptor proteins, though slightly different. Simultaneous computerized analysis of the data obtained by [3H]mepyramine binding to the solubilized [3H]mepyramine binding protein indicated the presence of a single binding site with a KD value of 19.0 +/- 5.6 nM and a binding capacity (Bmax) of 6.6 +/- 2.1 pmole/mg protein. The Ki value of cold mepyramine for [3H]mepyramine binding to the solubilized receptor was 20 +/- 4 nM, whereas those of diphenhydramine, d-chlorpheniramine and triprolidine were all 2.9 +/- 0.8 microM, or about 150 times that of mepyramine. These data on the molecular and binding characteristics of the solubilized protein reported here suggest that there is a subtype of histamine H1 receptor in rat liver membrane. The solubilized preparation retained 90% and 75% of its [3H]mepyramine binding activity after storage at -80 degrees C and 4 degrees C, respectively, for 20 days. The solubilized [3H]mepyramine binding protein was purified 30-fold by Sepharose CL-4B gel filtration, Bio Gel HTP hydroxylapatite, Octyl Sepharose 4B and hydroxylapatite HPLC column chromatographies.

Characterization of histamine H1-receptor on rat hepatocytes.

The binding sites for [3H]pyrilamine in isolated rat hepatocytes were characterized. Scatchard analysis revealed two kinds of binding sites in hepatocytes, a high-affinity site and a low-affinity one. The rates of binding of the radioligand with the high-affinity binding site and its dissociation were rapid. The specificity of the sites for various histamine antagonists indicated that the high-affinity [3H]pyrilamine binding site is representative of the histamine H1 receptor. Treatment of hepatocytes with protease or phospholipase A2 significantly decreased the maximum binding capacity of the high-affinity site without affecting its dissociation constant, suggesting that the binding site is proteinaceous and is sensitive to a change in the lipid moiety of the membrane. Hepatocytic cyclic AMP and cyclic GMP were not significantly modulated by incubating hepatocytes with histamine. Thus, the action of histamine on hepatocytes might not be mediated by the cyclic nucleotides.

Solubilization and Characterization of Histamine H1 receptors in brain.

[3H]Doxepin, a tricyclic antidepressant, binds with high affinity to guinea pig brain membranes with a drug specificity indicating an association with H1 histamine receptors. The [3H]doxepin binding site has been solubilized, with digitonin being the only detergent able to maintain specific binding after solubilization. After solubilization, the kinetics and drug specificity of binding are virtually identical with those obtained in the intact membranes, indicating a conservation of the transmitter binding site after removal of the receptor from its lipid environment. The regulation of agonist affinity for the histamine H1 receptor by cations is maintained after solubilization. Sodium and to a similar extent lithium, but not potassium, rubidium, or cesium, decrease the affinity of agonists for the receptor. The divalent cations manganese and magnesium maintain their ability to increase agonist affinity after solubilization. Guanine nucleotides, however, lose their ability to decrease agonist affinity for the histamine H1 receptor after solubilization. Histamine receptors in rat brain differ from guinea pig brain receptors in the potency of several antihistamines. The difference is maintained in the solubilized receptors. Sucrose gradient and gel filtration experiments indicated Mr approximately 430,000 for the receptor-digitonin complex. The isoelectric point of the receptor is 4.8. None of these physical techniques distinguishes between guinea pig and rat brain receptors.

Solubilization, separation, and partial characterization of histamine H1 and H2 receptors from calf thymocyte membranes.

Histamine membrane receptors are defined as either H1 (blocked by diphenhydramine-like antagonists) or H2 (blocked by cimetidine-like agents). We now report the solubilization, separation, and partial characterization of specific H1 and H2 membrane receptors from calf thymocytes. Membrane fragments were incubated with [3H]histamine either alone or with unlabeled histamine, diphenhydramine, or cimetidine. Maximal specific binding occurred with incubation at 37 degrees C for 2 h at a concentration of 5 x 10(-6) M [3H]histamine. Labeled receptors were solubilized from membranes with 0.3 M KCl and 1% Nonidet 40. Chromatography of the solubilized labeled receptors on ion exchange columns revealed two classes of receptor. One class bound to DEAE-cellulose and eluted as a sharp peak at 0.15 M NaCl/Pi. The other bound to phosphocellulose and eluted as a sharp peak at 0.55 M NaCl/Pi. Initial incubation of the membranes in the presence of the H1 receptor antagonist diphenhydramine virtually abolished the DEAE-cellulose peak, while incubation with cimetidine, the H2 receptor antagonist, blocked the phosphocellulose peak. We conclude that H1 and H2 histamine receptors are physically separable and can be defined by their ability to bind to either DEAE-cellulose or phosphocellulose.

Purification of histamine receptor (VI). An improved double labeling method with "double protection".

Studies were done on the specific labeling of the histaminergic H1-receptor of the longitudinal smooth muscle of cat small intestine. A procedure involving 'double protection' combined with the double labeling technique was developed. The first protection was the usual with a protective antihistamine, promethazine, and the second was cross protection of non-specific sites with non-hitaminergic drugs, thioriazine and atropine. Muscle tissue protected with promethazine against non-radioactive dibenamine was treated with 3H-dibenamine in the presence of these second protectors. The second protectors covered non-receptor sites which had been protected from non-radioactive dibenamine with promethazine. The dose-response curves were carefully checked in each experiment to confirm that the second protectors did not interfere with the specific coverage provided by the first protector. Finally 14C-dibenamine was applied to measure non-specific binding after which the labeled muscles were fractionated and the radioactivity was counted. The specificity of labeling achieved in the receptor-rich fraction by this method is discussed.