Proinflammatory chemokine CXCL14 activates MAS-related G protein-coupled receptor MRGPRX2 and its putative mouse ortholog MRGPRB2

Patients with idiopathic pulmonary fibrosis show a strongly upregulated expression of chemokine CXCL14, whose target is still unknown. Screening of CXCL14 in a panel of human G protein-coupled receptors (GPCRs) revealed its potent and selective activation of the orphan MAS-related GPCR X2 (MRGPRX2). This receptor is expressed on mast cells and - like CXCL14 - upregulated in bronchial inflammation. CXCL14 induces robust activation of MRGPRX2 and its putative mouse ortholog MRGPRB2 in G protein-dependent and β-arrestin recruitment assays that is blocked by a selective MRGPRX2/B2 antagonist. Truncation combined with mutagenesis and computational studies identified the pharmacophoric sequence of CXCL14 and its presumed interaction with the receptor. Intriguingly, C-terminal domain sequences of CXCL14 consisting of 4 to 11 amino acids display similar or increased potency and efficacy compared to the full CXCL14 sequence (77 amino acids). These results provide a rational basis for the future development of potential idiopathic pulmonary fibrosis therapies.

Age Impairs Soluble Guanylyl Cyclase Function in Mouse Mesenteric Arteries

Endothelial dysfunction (ED) comes with age, even without overt vessel damage such as that which occurs in atherosclerosis and diabetic vasculopathy. We hypothesized that aging would affect the downstream signalling of the endothelial nitric oxide (NO) system in the vascular smooth muscle (VSM). With this in mind, resistance mesenteric arteries were isolated from 13-week (juvenile) and 40-week-old (aged) mice and tested under isometric conditions using wire myography. Acetylcholine (ACh)-induced relaxation was reduced in aged as compared to juvenile vessels. Pretreatment with L-NAME, which inhibits nitrix oxide synthases (NOS), decreased ACh-mediated vasorelaxation, whereby differences in vasorelaxation between groups disappeared. Endothelium-independent vasorelaxation by the NO donor sodium nitroprusside (SNP) was similar in both groups; however, SNP bolus application (10⁻⁶ mol L⁻¹) as well as soluble guanylyl cyclase (sGC) activation by runcaciguat (10⁻⁶ mol L⁻¹) caused faster responses in juvenile vessels. This was accompanied by higher cGMP concentrations and a stronger response to the PDE5 inhibitor sildenafil in juvenile vessels. Mesenteric arteries and aortas did not reveal apparent histological differences between groups (van Gieson staining). The mRNA expression of the α1 and α2 subunits of sGC was lower in aged animals, as was PDE5 mRNA expression. In conclusion, vasorelaxation is compromised at an early age in mice even in the absence of histopathological alterations. Vascular smooth muscle sGC is a key element in aged vessel dysfunction.

Role of soluble guanylyl cyclase in renal afferent and efferent arterioles

Renal arteriolar tone depends considerably on the dilatory action of nitric oxide (NO) via activation of soluble guanylyl cyclase (sGC) and cGMP action. NO deficiency and hypoxia/reoxygenation are important pathophysiological factors in the development of acute kidney injury. It was hypothesized that the NO-sGC-cGMP system functions differently in renal afferent arterioles (AA) compared with efferent arterioles (EA) and that the sGC activator cinaciguat differentially dilates these arterioles. Experiments were performed in isolated, perfused mouse glomerular arterioles. Hypoxia (0.1% oxygen) was achieved by using a hypoxia chamber. Phosphodiesterase 5 (PDE5) and sGC subunits were considerably expressed on the mRNA level in AA. PDE5 inhibition with sildenafil, which blocks cGMP degradation, diminished the responses to ANG II bolus application in AA, but not significantly in EA. Vasodilation induced by sildenafil in ANG II-preconstricted vessels was stronger in EA than AA. Cinaciguat, an NO- and heme-independent sGC activator, dilated EA more strongly than AA after N^G-nitro-l-arginine methyl ester (l-NAME; NO synthase inhibitor) treatment and preconstriction with ANG II. Cinaciguat-induced dilatation of l-NAME-pretreated and ANG II-preconstricted arterioles was similar to controls without l-NAME treatment. Cinaciguat also induced dilatation in iodinated contrast medium treated AA. Furthermore, it dilated EA, but not AA, after hypoxia/reoxygenation. The results reveal an important role of the NO-sGC-cGMP system for renal dilatation and that EA have a more potent sGC activated dilatory system. Furthermore, AA seem to be more sensitive to hypoxia/reoxygenation than EA under these experimental conditions.

A Whole Genome-Wide Arrayed CRISPR Screen in Primary Organ Fibroblasts to Identify Regulators of Kidney Fibrosis

Kidney fibrosis presents a hallmark of chronic kidney disease. With ever-increasing patient numbers and limited treatment options available, novel strategies for therapeutic intervention in kidney disease are warranted. Fibrosis commonly results from a wound healing response to repeated or chronic tissue damage, irrespective of the underlying etiology, and can occur in virtually any solid organ or tissue. In order to identify targets relevant for kidney fibrosis, we aimed to employ CRISPR screening in primary human kidney fibroblasts. We demonstrate that CRISPR technology can be applied in primary kidney fibroblasts and can furthermore be used to conduct arrayed CRISPR screening using a high-content imaging readout in a whole genome-wide manner. Hits coming out of this screen were validated using orthogonal approaches and present starting points for validation of novel targets relevant to kidney disease.

Hypoxia/Reoxygenation of Rat Renal Arteries Impairs Vasorelaxation via Modulation of Endothelium-Independent sGC/cGMP/PKG Signaling

Ischemia/reperfusion injury holds a key position in many pathological conditions such as acute kidney injury and in the transition to chronic stages of renal damage. We hypothesized that besides a reported disproportional activation of vasoconstrictor response, hypoxia/reoxygenation (H/R) adversely affects endothelial dilatory systems and impairs relaxation in renal arteries. Rat renal interlobar arteries were studied under isometric conditions. Hypoxia was induced by application of 95% N₂, 5% CO₂ for 60 min to the bath solution, followed by a 10 min period of reoxygenation (95% O₂, 5% CO₂). The effect of H/R on relaxation was assessed using various inhibitors of endothelial dilatory systems. mRNA expression of phosphodiesterase 5 (PDE5), NADPH oxidases (NOX), and nitric oxide synthase (NOS) isoforms were determined using qRT-PCR; cGMP was assayed with direct cGMP ELISA. Acetylcholine induced relaxation was impaired after H/R. Inhibition of the NOS isoforms with L-NAME, and cyclooxygenases (COXs) by indomethacin did not abolish the H/R effect. Moreover, blocking the calcium activated potassium channels K_Ca3.1 and K_Ca2.1, the main mediators of the endothelium-derived hyperpolarizing factor, with TRAM34 and UCL1684, respectively, showed similar effects in H/R and control. Arterial stiffness did not differ comparing H/R with controls, indicating no impact of H/R on passive vessel properties. Moreover, superoxide was not responsible for the observed H/R effect. Remarkably, H/R attenuated the endothelium-independent relaxation by sodium nitroprusside, suggesting endothelium-independent mechanisms of H/R action. Investigating the signaling downstream of NO revealed significantly decreased cGMP and impaired relaxation during PDE5 inhibition with sildenafil after H/R. Inhibition of PKG, the target of cGMP, did not normalize SNP-induced relaxation following H/R. However, the soluble guanylyl cyclase (sGC) inhibitor ODQ abolished the H/R effect on relaxation. The mRNA expressions of the endothelial and the inducible NOS were reduced. NOX and PDE5 mRNA were similarly expressed in H/R and control. Our results provide new evidence that impaired renal artery relaxation after H/R is due to a dysregulation of sGC leading to decreased cGMP levels. The presented mechanism might contribute to an insufficient renal reperfusion after ischemia and should be considered in its pathophysiology.

Long-term levosimendan treatment improves systolic function and myocardial relaxation in mice with cardiomyocyte-specific disruption of the Serca2 gene

In human heart failure (HF), reduced cardiac function has, at least partly, been ascribed to altered calcium homeostasis in cardiomyocytes. The effects of the calcium sensitizer levosimendan on diastolic dysfunction caused by reduced removal of calcium from cytosol in early diastole are not well known. In this study, we investigated the effect of long-term levosimendan treatment in a murine model of HF where the sarco(endo)plasmatic reticulum ATPase (Serca) gene is specifically disrupted in the cardiomyocytes, leading to reduced removal of cytosolic calcium. After induction of Serca2 gene disruption, these mice develop marked diastolic dysfunction as well as impaired contractility. SERCA2 knockout (SERCA2KO) mice were treated with levosimendan or vehicle from the time of KO induction. At the 7-wk end point, cardiac function was assessed by echocardiography and pressure measurements. Vehicle-treated SERCA2KO mice showed significantly diminished left-ventricular (LV) contractility, as shown by decreased ejection fraction, stroke volume, and cardiac output. LV pressure measurements revealed a marked increase in the time constant (τ) of isovolumetric pressure decay, showing impaired relaxation. Levosimendan treatment significantly improved all three systolic parameters. Moreover, a significant reduction in τ toward normalization indicated improved relaxation. Gene-expression analysis, however, revealed an increase in genes related to production of the ECM in animals treated with levosimendan. In conclusion, long-term levosimendan treatment improves both contractility and relaxation in a heart-failure model with marked diastolic dysfunction due to reduced calcium transients. However, altered gene expression related to fibrosis was observed.

Myocardial transcriptome analysis of human arrhythmogenic right ventricular cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiomyopathy primarily of the right ventricle characterized through fibrofatty replacement of cardiomyocytes. The genetic etiology in ARVC patients is most commonly caused by dominant inheritance and high genetic heterogeneity. Though histological examinations of ARVC-affected human myocardium reveals fibrolipomatous replacement, the molecular mechanisms leading to loss of cardiomyocytes are largely unknown. We therefore analyzed the transcriptomes of six ARVC hearts and compared our findings to six nonfailing donor hearts (NF). To characterize the ARVC-specific transcriptome, we compared our findings to samples from seven patients with idiopathic dilated cardiomyopathy (DCM). The myocardial DCM and ARVC samples were prepared from hearts explanted during an orthotopic heart transplantation representing myocardium from end-stage heart failure patients (NYHA IV). From each heart, left (LV) and right ventricular (RV) myocardial samples were analyzed by Affymetrix HG-U133 Plus 2.0 arrays, adding up to six sample groups. Unsupervised cluster analyses of the groups revealed a clear separation of NF and cardiomyopathy samples. However, in contrast to the other samples, the analyses revealed no distinct expression pattern in LV and RV of myocardial ARVC samples. We further identified differentially expressed transcripts using t-tests and found transcripts separating diseased and NF ventricular myocardium. Of note, in failing myocardium only ~15-16% of the genes are commonly regulated compared with NF samples. In addition both cardiomyopathies are clearly distinct on the transcriptome level. Comparison of the expression patterns between the failing RV and LV using a paired t-test revealed a lack of major differences between LV and RV gene expression in ARVC hearts. Our study is the first analysis of specific ARVC-related RV and LV gene expression patterns in terminal failing human hearts.

Charcot-Marie-Tooth disease CMT4A: GDAP1 increases cellular glutathione and the mitochondrial membrane potential

Mutations in GDAP1 lead to recessively or dominantly inherited peripheral neuropathies (Charcot-Marie-Tooth disease, CMT), indicating that GDAP1 is essential for the viability of cells in the peripheral nervous system. GDAP1 contains domains characteristic of glutathione-S-transferases (GSTs), is located in the outer mitochondrial membrane and induces fragmentation of mitochondria. We found GDAP1 upregulated in neuronal HT22 cells selected for resistance against oxidative stress. GDAP1 over-expression protected against oxidative stress caused by depletion of the intracellular antioxidant glutathione (GHS) and against effectors of GHS depletion that affect the mitochondrial membrane integrity like truncated BH3-interacting domain death agonist and 12/15-lipoxygenase. Gdap1 knockdown, in contrast, increased the susceptibility of motor neuron-like NSC34 cells against GHS depletion. Over-expression of wild-type GDAP1, but not of GDAP1 with recessively inherited mutations that cause disease and reduce fission activity, increased the total cellular GHS content and the mitochondrial membrane potential up to a level where it apparently limits mitochondrial respiration, leading to reduced mitochondrial Ca(2+) uptake and superoxide production. Fibroblasts from autosomal-recessive CMT4A patients had reduced GDAP1 levels, reduced GHS concentration and a reduced mitochondrial membrane potential. Thus, our results suggest that the potential GST GDAP1 is implicated in the control of the cellular GHS content and mitochondrial activity, suggesting an involvement of oxidative stress in the pathogenesis of CMT4A.

TOX3 is a neuronal survival factor that induces transcription depending on the presence of CITED1 or phosphorylated CREB in the transcriptionally active complex

TOX3 is a nuclear protein containing a high mobility group (HMG)-box domain, which regulates Ca(2+)-dependent transcription in neurons through interaction with the cAMP-response-element-binding protein (CREB). TOX3 appears to be associated with breast cancer susceptibility and was previously shown to be expressed downstream of a cytoprotective cascade together with CITED1, a transcriptional regulator that does not bind directly to DNA. In the present study we show that TOX3 is predominantly expressed in the brain, forms homodimers and interacts with CITED1. TOX3 overexpression protects neuronal cells from cell death caused by endoplasmic reticulum stress or BAX overexpression through the induction of anti-apoptotic transcripts and repression of pro-apoptotic transcripts, which correlates with enhanced transcription involving isolated estrogen-responsive elements and estrogen-responsive promoters. However, both functions cannot be inhibited with the anti-estrogen fulvestrant and are only attenuated by mutation of estrogen-responsive elements. TOX3 also interacts with native CREB and induces the CREB-responsive BCL-2 promoter, which can be inhibited by coexpression of CITED1. Coexpression of CREB, by contrast, abolishes TOX3-mediated transcription from the estrogen-responsive complement C3 promoter. Our results suggest that TOX3 can enhance transcriptional activation from different cytoprotective promoters and that this is dependent on the predominance of either phosphorylated CREB or CITED1 within the transcriptionally active complex.

NMR-derived topology of a GFP-photoprotein energy transfer complex

Förster resonance energy transfer within a protein-protein complex has previously been invoked to explain emission spectral modulation observed in several bioluminescence systems. Here we present a spatial structure of a complex of the Ca(2+)-regulated photoprotein clytin with its green-fluorescent protein (cgGFP) from the jellyfish Clytia gregaria, and show that it accounts for the bioluminescence properties of this system in vitro. We adopted an indirect approach of combining x-ray crystallography determined structures of the separate proteins, NMR spectroscopy, computational docking, and mutagenesis. Heteronuclear NMR spectroscopy using variously (15)N,(13)C,(2)H-enriched proteins enabled assignment of backbone resonances of more than 94% of the residues of both proteins. In a mixture of the two proteins at millimolar concentrations, complexation was inferred from perturbations of certain (1)H-(15)N HSQC-resonances, which could be mapped to those residues involved at the interaction site. A docking computation using HADDOCK was employed constrained by the sites of interaction, to deduce an overall spatial structure of the complex. Contacts within the clytin-cgGFP complex and electrostatic complementarity of interaction surfaces argued for a weak protein-protein complex. A weak affinity was also observed by isothermal titration calorimetry (K(D) = 0.9 mM). Mutation of clytin residues located at the interaction site reduced the degree of protein-protein association concomitant with a loss of effectiveness of cgGFP in color-shifting the bioluminescence. It is suggested that this clytin-cgGFP structure corresponds to the transient complex previously postulated to account for the energy transfer effect of GFP in the bioluminescence of aequorin or Renilla luciferase.

Green-fluorescent protein from the bioluminescent jellyfish Clytia gregaria: cDNA cloning, expression, and characterization of novel recombinant protein

The bioluminescent systems of many marine organisms are comprised of two proteins--the Ca(2+)-regulated photoprotein and green-fluorescent protein (GFP). This work reports the cloning of the full-size cDNA encoding GFP (cgreGFP) from jellyfish Clytia gregaria, its expression and properties of the recombinant protein. The overall degree of identity between the amino acid sequence of the novel cgreGFP and the sequence of GFP (avGFP) from Aequorea victoria is 42% (similarity--64%) despite these GFPs originating from jellyfish that both belong to the same class, Hydrozoa. However although the degree of identity is low, three residues, Ser-Tyr-Gly, which form the chromophore are identical in both GFPs. The cgreGFP displayed two absorption peaks at 278 and 485 nm, and the fluorescence maximum at 500 nm. The fluorescence quantum yield was determined to be 0.86, the brightness to be 54 mM(-1) cm(-1). For the first time we have also demonstrated an efficient radiationless energy transfer in vitro between clytin and cgreGFP in solution at micromolar concentrations. The cgreGFP may be a useful intracellular fluorescent marker, as it was able to be expressed in mammalian cells.

A novel giant peroxisomal superoxide dismutase motif-containing protein

Oxidative glutamate toxicity in the neuronal cell line HT22 is a model for neuronal cell death by oxidative stress. In this model, extracellular glutamate blocks cystine uptake via the glutamate/cystine antiporter system x(c)(), eventually leading to depletion of the antioxidant glutathione and cell death. We used subtractive suppression hybridization and a screening procedure using various HT22 sublines to identify transcripts relevantly upregulated in resistance to oxidative glutamate toxicity. One of these coded for a novel protein of 3440 amino acids comprising a superoxide dismutase (SOD) motif, which we named TIGR for "transcript increased in glutamate resistance." TIGR is mainly expressed in the nervous system in cortical pyramidal and hippocampal neurons. Intracellularly, TIGR colocalizes with catalase, strongly suggesting a peroxisomal localization. Overexpression of TIGR but not of a mutant lacking two conserved histidine residues in the SOD motif increased SOD activity and protected against oxidative stress in mammalian cells, but had no direct SOD activity in yeast. We conclude that this novel giant peroxisomal protein is implicated in resistance to oxidative stress. Despite the presence of a SOD motif, which is necessary for protection in mammalian cells, the protein is not a functional SOD, but might be involved in SOD activity.

Genomic profiling of developing cardiomyocytes from recombinant murine embryonic stem cells reveals regulation of transcription factor clusters

Cardiomyocytes derived from pluripotent embryonic stem cells (ESC) have the advantage of providing a source for standardized cell cultures. However, little is known on the regulation of the genome during differentiation of ESC to cardiomyocytes. Here, we characterize the transcriptome of the mouse ESC line CM7/1 during differentiation into beating cardiomyocytes and compare the gene expression profiles with those from primary adult murine cardiomyocytes and left ventricular myocardium. We observe that the cardiac gene expression pattern of fully differentiated CM7/1-ESC is highly similar to adult primary cardiomyocytes and murine myocardium, respectively. This finding is underlined by demonstrating pharmacological effects of catecholamines and endothelin-1 on ESC-derived cardiomyocytes. Furthermore, we monitor the temporal changes in gene expression pattern during ESC differentiation with a special focus on transcription factors involved in cardiomyocyte differentiation. Thus, CM7/1-ESC-derived cardiomyocytes are a promising new tool for functional studies of cardiomyocytes in vitro and for the analysis of the transcription factor network regulating pluripotency and differentiation to cardiomyocytes.

The constitutively active orphan G-protein-coupled receptor GPR39 protects from cell death by increasing secretion of pigment epithelium-derived growth factor

GPR39 is a constitutively active orphan G-protein-coupled receptor capable of increasing serum response element-mediated transcription. We found GPR39 to be up-regulated in a hippocampal cell line resistant against diverse stimulators of cell death and show that its overexpression protects against oxidative and endoplasmic reticulum stress, as well as against direct activation of the caspase cascade by Bax overexpression. In contrast, silencing GPR39 rendered cells more susceptible to cell death. An array analysis of transcripts induced by GPR39 revealed up-regulation of RGS16 (inhibitor of G-protein signaling 16), which suggested coupling to Galpha(13) and induction of serum response element-mediated transcription by the small GTPase RhoA. In line with this, co-expression of GPR39 with RGS16, dominant-negative RhoA, or serum response factor abolished cell protection, whereas overexpression of the serum response factor protected from cell death. Further downstream the signaling cascade, GPR39 overexpression leads to increased secretion of the cytoprotective pigment epithelium-derived growth factor (PEDF). Medium conditioned by cells overexpressing GPR39 contained 4-fold more PEDF, and when stripped off it lost most but not all of its protective properties. We conclude that GPR39 is a novel inhibitor of cell death, which might represent a therapeutic target with implications for processes involving apoptosis and endoplasmic reticulum stress like cancer, ischemia/reperfusion injury, and neurodegenerative disease.

Probing the substrate specificity of the ergothioneine transporter with methimazole, hercynine, and organic cations

Recently, we have identified the ergothioneine (ET) transporter ETT (gene symbol SLC22A4). Much interest in human ETT has been generated by case-control studies that suggest an association of polymorphisms in the SLC22A4 gene with susceptibility to chronic inflammatory diseases. ETT was originally designated a multispecific novel organic cation transporter (OCTN1). Here we reinvestigated, based on stably transfected 293 cells and with ET as reference substrate, uptake of quinidine, verapamil, and pyrilamine. ETT from human robustly catalyzed transport of ET (68micfrol/(minmgprotein)), but no transport of organic cations was discernible. With ET as substrate, ETT was relatively resistant to inhibition by selected drugs; the most potent inhibitor was verapamil (K(i)=11micromol/l). The natural compound hercynine and antithyroid drug methimazole are related in structure to ET. However, efficiency of ETT-mediated transport of methimazole (K(i)=7.5mmol/l) was 130-fold lower, and transport of hercynine (K(i)=1.4mmol/l) was 25-fold lower than transport of ET. ETT from mouse, upon expression in 293 cells, catalyzed high affinity, sodium-driven uptake of ET very similar to ETT from human. Additional real-time PCR experiments based on 16 human tissues revealed ETT mRNA levels considerably lower than in bone marrow. Our experiments establish that ETT is highly specific for its physiological substrate ergothioneine. ETT is not a cationic drug transporter, and it does not have high affinity for organic cation inhibitors. Detection of ETT mRNA or protein can therefore be utilized as a specific molecular marker of intracellular ET activity.

Large-scale, high-throughput validation of short hairpin RNA sequences for RNA interference

A method for high-throughput cloning and analysis of short hairpin RNAs (shRNAs) is described. Using this approach, 464 shRNAs against 116 different genes were screened for knockdown efficacy, enabling rapid identification of effective shRNAs against 74 genes. Statistical analysis of the effects of various criteria on the activity of the shRNAs confirmed that some of the rules thought to govern small interfering RNA (siRNA) activity also apply to shRNAs. These include moderate GC content, absence of internal hairpins, and asymmetric thermal stability. However, the authors did not find strong support for position specific rules. In addition, analysis of the data suggests that not all genes are equally susceptible to RNA interference (RNAi).

Discovery of the ergothioneine transporter

Variants of the SLC22A4 gene are associated with susceptibility to rheumatoid arthritis and Crohn's disease. SLC22A4 codes for an integral membrane protein, OCTN1, that has been presumed to carry organic cations like tetraethylammonium across the plasma membrane. Here, we show that the key substrate of this transporter is in fact ergothioneine (ET). Human OCTN1 was expressed in 293 cells. A substrate lead, stachydrine (alias proline betaine), was identified by liquid chromatography MS difference shading, a new substrate search strategy. Analysis of transport efficiency of stachydrine-related solutes, affinity, and Na+ dependence indicates that the physiological substrate is ET. Efficiency of transport of ET was as high as 195 microl per min per mg of protein. By contrast, the carnitine transporter OCTN2 from rat did not transport ET at all. Because ET is transported >100 times more efficiently than tetraethylammonium and carnitine, we propose the functional name ETT (ET transporter) instead of OCTN1. ET, all of which is absorbed from food, is an intracellular antioxidant with metal ion affinity. Its particular purpose is unresolved. Cells with expression of ETT accumulate ET to high levels and avidly retain it. By contrast, cells lacking ETT do not accumulate ET, because their plasma membrane is virtually impermeable for this compound. The real-time PCR expression profile of human ETT, with strong expression in CD71+ cells, is consistent with a pivotal function of ET in erythrocytes. Moreover, prominent expression of ETT in monocytes and SLC22A4 polymorphism associations suggest a protective role of ET in chronic inflammatory disorders.

Interchange of aequorin and obelin bioluminescence color is determined by substitution of one active site residue of each photoprotein

The bioluminescence spectra from the Ca2+-regulated photoproteins aequorin (lambdamax=469 nm) and obelin (lambdamax=482 nm) differ because aequorin has an H-bond from its Tyr82 to the bound coelenteramide, not present in obelin at the corresponding Phe88. Substitutions of this Phe88 by Tyr, Trp, or His shifted the obelin bioluminescence to shorter wavelength with F88Y having lambdamax=453 nm. Removal of the H-bond by the substitution of Y82F in aequorin shifted its bioluminescence to lambdamax=501 nm. All mutants were stable with good activity and were expressible in mammalian cells, thereby demonstrating potential for monitoring multiple events in cells using multi-color detection.

Cloning and expression of cDNA for a luciferase from the marine copepod Metridia longa. A novel secreted bioluminescent reporter enzyme

Metridia longa is a marine copepod from which a blue bioluminescence originates as a secretion from epidermal glands in response to various stimuli. We demonstrate that Metridia luciferase is specific for coelenterazine to produce blue light (lambda(max) = 480 nm). Using an expression cDNA library and functional screening, we cloned and sequenced the cDNA encoding the Metridia luciferase. The cDNA is an 897-bp fragment with a 656-bp open reading frame, which encodes a 219-amino acid polypeptide with a molecular weight of 23,885. The polypeptide contains an N-terminal signal peptide of 17 amino acid residues for secretion. On expression of the Metridia luciferase gene in mammalian Chinese hamster ovary cells the luciferase is detected in the culture medium confirming the existence of a naturally occurring signal peptide for secretion in the cloned luciferase. The novel secreted luciferase was tested in a practical assay application in which the activity of A2a and NPY2 G-protein-coupled receptors was detected. These results clearly suggest that the secreted Metridia luciferase is well suited as a reporter for monitoring gene expression and, in particular, for the development of novel ultrahigh throughput screening technologies.

Enzymatic mutation detection: enrichment of heteroduplexes from hybrid DNA mixtures by cleavage-deficient GST-tagged endonuclease VII

A method for the enrichment of heteroduplex DNAs from hybrid DNA mixtures by endonuclease VII is reported. The procedure is based on the ability of a GST-fused cleavage-deficient mutant endonuclease VII (EVII-N62D(GST)) to bind to mismatching nucleotides in heteroduplex DNAs identical to the wild-type enzyme. The GST tag was used for stable immobilisation of the protein to Glutathione Sepharose 4B. This enables the material to withstand the repeated rounds of binding steps required for enrichment of heteroduplex molecules from appropriate samples.

X-ray structure of T4 endonuclease VII: a DNA junction resolvase with a novel fold and unusual domain-swapped dimer architecture

Phage T4 endonuclease VII (Endo VII), the first enzyme shown to resolve Holliday junctions, recognizes a broad spectrum of DNA substrates ranging from branched DNAs to single base mismatches. We have determined the crystal structures of the Ca2+-bound wild-type and the inactive N62D mutant enzymes at 2.4 and 2.1 A, respectively. The Endo VII monomers form an elongated, highly intertwined molecular dimer exhibiting extreme domain swapping. The major dimerization elements are two pairs of antiparallel helices forming a novel 'four-helix cross' motif. The unique monomer fold, almost completely lacking beta-sheet structure and containing a zinc ion tetrahedrally coordinated to four cysteines, does not resemble any of the known junction-resolving enzymes, including the Escherichia coli RuvC and lambda integrase-type recombinases. The S-shaped dimer has two 'binding bays' separated by approximately 25 A which are lined by positively charged residues and contain near their base residues known to be essential for activity. These include Asp40 and Asn62, which function as ligands for the bound calcium ions. A pronounced bipolar charge distribution suggests that branched DNA substrates bind to the positively charged face with the scissile phosphates located near the divalent cations. A model for the complex with a four-way DNA junction is presented.

Association of holliday-structure resolving endonuclease VII with gp20 from the packaging machine of phage T4

Endonuclease VII (endo VII) is the product of gene 49 (gp49) of bacteriophage T4. It is a Holliday-structure resolvase (X-solvase) responsible for clearing branched replicative DNA prior to packaging. Consequently, mutations in gene 49 are unable to fill heads to completion because unresolved branches stop translocation of DNA. A likely association of gp49 with heads or proheads, however, could not be shown in the past. We have investigated whether gp49 could be part of the transiently assembled packaging machine (the "packasome") located at the base of proheads. Using purified proteins gpl6, gpl7 and gp20, which are constituents of the packasome, we found that gp49 binds tightly to gp20 and does not bind to gpl6 or gpl7. Quantification revealed that one dimer of gp49 binds one monomer of gp20. Notably, dimerisation of gp49 was an essential prerequisite for complex formation with gp20, and the dimerisation-deficient point mutation His-EVII-W87R showed only residual affinity to gp20. Furthermore, truncated peptides of gp49 deficient in dimer formation to various degrees were found to be impaired in binding to gp20. In contrast, the cleavage-deficient mutation EVII-N62D bound normally to gp20. The cruciform DNA (cf-DNA) resolving activity typical of endo VII is maintained in gp20-gp49 complexes. Furthermore, the complexes bind cf-DNA in the absence of Mg2+ as demonstrated by electromobility shift assays. The binding of the complexes to cf-DNA occurs via gp49, since gp20 alone does not bind cf-DNA. In conclusion, these findings are consistent with a model in which gp49 is an integral part of the packaging machine of phage T4.

Enzymatic mutation detection. Phosphate ions increase incision efficiency of endonuclease VII at a variety of damage sites in DNA

The ability of endonuclease VII (endo VII) to cleave at mispairings in double-stranded DNA has recently been used for enzymatic mutation detection (EMD) [R. Youil, B.W. Kemper, R.G.H. Cotton, Proc. Natl. Acad. Sci. USA 92 (1995) 87-91]. The method is based on mapping cleavages in heteroduplex DNAs obtained from mutant and wildtype sequences. Despite the capability of endo VII to cleave at all possible mispairings, relative cleavage efficiencies vary considerably for individual mismatches and may escape detection if located in an unfavorable sequence surrounding. We report here improved reaction conditions which can increase the selectivity of the enzyme for mismatches up to 500-fold, as demonstrated with a mutation in a 247 nt long fragment from exon 7 of human gene p53. The new conditions involve replacement of Tris/HCl buffer by phosphate buffer and change from pH 8.0 to 6.5. Various concentrations of phosphate ions should be tried in the assay to meet individual requirements of the substrate.

Enzymatic mutation detection. Procedure for screening and mapping of mutations by immobilised endonuclease VII

Endonuclease VII (endo VII) binds to non-pairing nucleotides in DNA. This served as the basis for the development of a mutation detection assay involving immobilised endo VII and heteroduplex DNAs made by hybridisation of mutant and wild type DNA. The use of microtiter plates allows screening of large numbers of samples. Localisation of mutations in positive samples can be done in the same assay in a second optional step.

Identification of amino acids of endonuclease VII essential for binding and cleavage of cruciform DNA

Endonuclease VII is a Holliday-structure-resolving enzyme of bacteriophage T4. The active protein is a homodimer with 157 amino acids/monomer. An amber mutation (amE727 in codon 151) inactivates the nuclease completely, indicating the importance of the seven C-terminal amino acids for nucleolytic activity. The influence of these amino acids on cruciform-DNA binding and cleavage was investigated through functional analysis of C-terminal-truncated proteins derived from deletion constructs. It was found that the three C-terminal amino acids are not necessary for binding and cleavage. A transition from active to inactive protein occurs gradually with truncations of the next four amino acids. Reduction of DNA-binding ability, as measured by electrophoretic mobility shift assays, was determined to be the primary defect in the cleavage-deficient proteins. This was further concluded by the finding that EVII-(1-150)-peptide(amber), a protein with fairly low affinity to cruciform DNA, contributes cleavage activity to reactions of wild-type EVII with cruciform DNA. [Asp62]EVII-(1-156)-peptide lacking one C-terminal amino acid, contains a point mutation in codon 62 that eliminates the nucleolytic activity of the protein while retaining its DNA-binding proficiency. By mixing binding-deficient and cleavage-deficient mutants in the same assay, cleavage of cruciform DNA resumed. Evidence is presented that complementation occurs by heterodimer formation. Our results show that the zinc-binding motif of EVII is not sufficient for cruciform-DNA binding.

Inhibition of Holliday structure resolving endonuclease VII of bacteriophage T4 by recombination enzymes UvsX and UvsY

Proteins UvsX, UvsY and Endonuclease VII (Endo VII) of bacteriophage T4 are required for DNA recombination, replication and repair. Endo VII is the product of gene 49 (gp49) and essential for resolution of branches from newly made DNA, prior to packaging into preformed heads. The ability of Endo VII to resolve Holliday structures in vitro suggested an in vivo function for the resolution of recombination intermediates, generated by UvsX and UvsY during the early infection cycle. Here we report results which contrast with this hypothesis. It is shown that the potent endonucleolytic activity of Endo VII with branched DNAs is inhibited in strand transfer reactions by the strand transferase UvsX, and more strongly by the accessory protein UvsY in vitro. The inhibitory effect of UvsX or UvsY is also seen in reactions with Endo VII using two synthetic cruciform DNAs and a C/C-mismatch containing substrate. Low concentrations of UvsY protein (12 ng or 0,76 pmol) were sufficient to reduce the cleavage efficiency of 30 units of Endo VII (about 16 fmol) to 50%. The inhibition is due to a direct protein-protein interaction between Endo VII, UvsX and UvsY as suggested by electrophoretic mobility shift assays (EMSAs). These results were confirmed through affinity chromatography, where UvsX and UvsY bound to Endo VII, immobilized on a NHS-activated Sepharose matrix. This is the first identification of phage-encoded proteins which modulate the potent endonucleolytic activity of gp49 in vitro.

Improved large-scale preparation of phage T4 endonuclease VII overexpressed in E. coli

Using PCR, we cloned T4 gene 49, which encodes the endonuclease VII, and the inactive mutant gene 49 amE727 into vector pET-11a. In combination with Escherichia coli host strain BL21 (DE3), this system provided excellent repression of the expression of the highly toxic protein before induction with IPTG. After induction, the proteins were made in high quantities while remaining soluble. Dilution of the crude lysate at 1:10,000 continued to show a highly specific activity in the case of the wild-type enzyme. The protein was purified to homogeneity with a recovery of 33% using two chromatography steps. The yield was 20 times higher and the specific activity 500 times higher than that obtained by using the previously published protocol.