Microbially Induced Calcium Carbonate Precipitation by Sporosarcina pasteurii: a Case Study in Optimizing Biological CaCO3 Precipitation

Current production of traditional concrete requires enormous energy investment that accounts for approximately 5 to 8% of the world's annual CO2 production. Biocement is a building material that is already in industrial use and has the potential to rival traditional concrete as a more convenient and more environmentally friendly alternative. Biocement relies on biological structures (enzymes, cells, and/or cellular superstructures) to mineralize and bind particles in aggregate materials (e.g., sand and soil particles). Sporosarcina pasteurii is a workhorse organism for biocementation, but most research to date has focused on S. pasteurii as a building material rather than a biological system. In this review, we synthesize available materials science, microbiology, biochemistry, and cell biology evidence regarding biological CaCO3 precipitation and the role of microbes in microbially induced calcium carbonate precipitation (MICP) with a focus on S. pasteurii. Based on the available information, we provide a model that describes the molecular and cellular processes involved in converting feedstock material (urea and Ca2+) into cement. The model provides a foundational framework that we use to highlight particular targets for researchers as they proceed into optimizing the biology of MICP for biocement production.

Design of a minimal di-nickel hydrogenase peptide

Ancestral metabolic processes involve the reversible oxidation of molecular hydrogen by hydrogenase. Extant hydrogenase enzymes are complex, comprising hundreds of amino acids and multiple cofactors. We designed a 13-amino acid nickel-binding peptide capable of robustly producing molecular hydrogen from protons under a wide variety of conditions. The peptide forms a di-nickel cluster structurally analogous to a Ni-Fe cluster in [NiFe] hydrogenase and the Ni-Ni cluster in acetyl-CoA synthase, two ancient, extant proteins central to metabolism. These experimental results demonstrate that modern enzymes, despite their enormous complexity, likely evolved from simple peptide precursors on early Earth.

Design of a Fe4 S4 cluster into the core of a de novo four-helix bundle

We explore the capacity of the de novo protein, S824, to incorporate a multinuclear iron-sulfur cluster within the core of a single-chain four-helix bundle. This topology has a high intrinsic designability because sequences are constrained largely by the pattern of hydrophobic and hydrophilic amino acids, thereby allowing for the extensive substitution of individual side chains. Libraries of novel proteins based on these constraints have surprising functional potential and have been shown to complement the deletion of essential genes in E. coli. Our structure-based design of four first-shell cysteine ligands, one per helix, in S824 resulted in successful incorporation of a cubane Fe₄ S₄ cluster into the protein core. A number of challenges were encountered during the design and characterization process, including nonspecific metal-induced aggregation and the presence of competing metal-cluster stoichiometries. The introduction of buried iron-sulfur clusters into the helical bundle is an initial step toward converting libraries of designed structures into functional de novo proteins with catalytic or electron-transfer functionalities.

De novo synthetic biliprotein design, assembly and excitation energy transfer

Bilins are linear tetrapyrrole chromophores with a wide range of visible and near-visible light absorption and emission properties. These properties are tuned upon binding to natural proteins and exploited in photosynthetic light-harvesting and non-photosynthetic light-sensitive signalling. These pigmented proteins are now being manipulated to develop fluorescent experimental tools. To engineer the optical properties of bound bilins for specific applications more flexibly, we have used first principles of protein folding to design novel, stable and highly adaptable bilin-binding four-α-helix bundle protein frames, called maquettes, and explored the minimal requirements underlying covalent bilin ligation and conformational restriction responsible for the strong and variable absorption, fluorescence and excitation energy transfer of these proteins. Biliverdin, phycocyanobilin and phycoerythrobilin bind covalently to maquette Cys in vitro A blue-shifted tripyrrole formed from maquette-bound phycocyanobilin displays a quantum yield of 26%. Although unrelated in fold and sequence to natural phycobiliproteins, bilin lyases nevertheless interact with maquettes during co-expression in Escherichia coli to improve the efficiency of bilin binding and influence bilin structure. Bilins bind in vitro and in vivo to Cys residues placed in loops, towards the amino end or in the middle of helices but bind poorly at the carboxyl end of helices. Bilin-binding efficiency and fluorescence yield are improved by Arg and Asp residues adjacent to the ligating Cys on the same helix and by His residues on adjacent helices.

Rational Construction of Compact de Novo-Designed Biliverdin-Binding Proteins

We report the rational construction of de novo-designed biliverdin-binding proteins by first principles of protein design, informed by energy minimization modeling in Rosetta. The self-assembling tetrahelical bundles bind biliverdin IXa (BV) cofactor autocatalytically in vitro, like photosensory proteins that bind BV (and related bilins or linear tetrapyrroles) despite lacking sequence and structural homology to the natural counterparts. Upon identification of a suitable site for ligation of the cofactor to the protein scaffold, stepwise placement of residues stabilized BV within the hydrophobic core. Rosetta modeling was used in the absence of a high-resolution structure to inform the structure-function relationships of the cofactor binding pocket. Holoprotein formation stabilized BV, resulting in increased far-red BV fluorescence. Via removal of segments extraneous to cofactor stabilization or bundle stability, the initial 15 kDa de novo-designed fluorescence-activating protein was truncated without any change to its optical properties, down to a miniature 10 kDa "mini", in which the protein scaffold extends only a half-heptad repeat beyond the hypothetical position of the bilin D-ring. This work demonstrates how highly compact holoprotein fluorochromes can be rationally constructed using de novo protein design technology and natural cofactors.

A synthetic biological quantum optical system

In strong plasmon-exciton coupling, a surface plasmon mode is coupled to an array of localized emitters to yield new hybrid light-matter states (plexcitons), whose properties may in principle be controlled via modification of the arrangement of emitters. We show that plasmon modes are strongly coupled to synthetic light-harvesting maquette proteins, and that the coupling can be controlled via alteration of the protein structure. For maquettes with a single chlorin binding site, the exciton energy (2.06 ± 0.07 eV) is close to the expected energy of the Qy transition. However, for maquettes containing two chlorin binding sites that are collinear in the field direction, an exciton energy of 2.20 ± 0.01 eV is obtained, intermediate between the energies of the Qx and Qy transitions of the chlorin. This observation is attributed to strong coupling of the LSPR to an H-dimer state not observed under weak coupling.

Multi-step excitation energy transfer engineered in genetic fusions of natural and synthetic light-harvesting proteins

Synthetic proteins designed and constructed from first principles with minimal reference to the sequence of any natural protein have proven robust and extraordinarily adaptable for engineering a range of functions. Here for the first time we describe the expression and genetic fusion of a natural photosynthetic light-harvesting subunit with a synthetic protein designed for light energy capture and multi-step transfer. We demonstrate excitation energy transfer from the bilin of the CpcA subunit (phycocyanin α subunit) of the cyanobacterial photosynthetic light-harvesting phycobilisome to synthetic four-helix-bundle proteins accommodating sites that specifically bind a variety of selected photoactive tetrapyrroles positioned to enhance energy transfer by relay. The examination of combinations of different bilin, chlorin and bacteriochlorin cofactors has led to identification of the preconditions for directing energy from the bilin light-harvesting antenna into synthetic protein-cofactor constructs that can be customized for light-activated chemistry in the cell.

Design and engineering of water-soluble light-harvesting protein maquettes

Natural selection in photosynthesis has engineered tetrapyrrole based, nanometer scale, light harvesting and energy capture in light-induced charge separation. By designing and creating nanometer scale artificial light harvesting and charge separating proteins, we have the opportunity to reengineer and overcome the limitations of natural selection to extend energy capture to new wavelengths and to tailor efficient systems that better meet human as opposed to cellular energetic needs. While tetrapyrrole cofactor incorporation in natural proteins is complex and often assisted by accessory proteins for cofactor transport and insertion, artificial protein functionalization relies on a practical understanding of the basic physical chemistry of protein and cofactors that drive nanometer scale self-assembly. Patterning and balancing of hydrophobic and hydrophilic tetrapyrrole substituents is critical to avoid natural or synthetic porphyrin and chlorin aggregation in aqueous media and speed cofactor partitioning into the non-polar core of a man-made water soluble protein designed according to elementary first principles of protein folding. This partitioning is followed by site-specific anchoring of tetrapyrroles to histidine ligands strategically placed for design control of rates and efficiencies of light energy and electron transfer while orienting at least one polar group towards the aqueous phase.

Constructing a man-made c-type cytochrome maquette in vivo: electron transfer, oxygen transport and conversion to a photoactive light harvesting maquette

The successful use of man-made proteins to advance synthetic biology requires both the fabrication of functional artificial proteins in a living environment, and the ability of these proteins to interact productively with other proteins and substrates in that environment. Proteins made by the maquette method integrate sophisticated oxidoreductase function into evolutionarily naive, non-computationally designed protein constructs with sequences that are entirely unrelated to any natural protein. Nevertheless, we show here that we can efficiently interface with the natural cellular machinery that covalently incorporates heme into natural cytochromes c to produce in vivo an artificial c-type cytochrome maquette. Furthermore, this c-type cytochrome maquette is designed with a displaceable histidine heme ligand that opens to allow functional oxygen binding, the primary event in more sophisticated functions ranging from oxygen storage and transport to catalytic hydroxylation. To exploit the range of functions that comes from the freedom to bind a variety of redox cofactors within a single maquette framework, this c-type cytochrome maquette is designed with a second, non-heme C, tetrapyrrole binding site, enabling the construction of an elementary electron transport chain, and when the heme C iron is replaced with zinc to create a Zn porphyrin, a light-activatable artificial redox protein. The work we describe here represents a major advance in de novo protein design, offering a robust platform for new c-type heme based oxidoreductase designs and an equally important proof-of-principle that cofactor-equipped man-made proteins can be expressed in living cells, paving the way for constructing functionally useful man-made proteins in vivo.

L-454,560, a potent and selective PDE4 inhibitor with in vivo efficacy in animal models of asthma and cognition

Type 4 phosphodiesterases (PDE4) inhibitors are emerging therapeutics in the treatment of a number of chronic disorders including asthma, chronic obstructive pulmonary disease (COPD) and cognitive disorders. This study delineates the preclinical profile of L-454,560, which is a potent, competitive and preferential inhibitor of PDE4A, 4B, and 4D with IC50 values of 1.6, 0.5 and 1.2 nM, respectively. In contrast to the exclusive binding of cilomilast and the preferential binding of roflumilast to the PDE4 holoenzyme state (Mg2+-bound form), L-454,560 binds to both the apo-(Mg2+-free) and holoenzyme states of PDE4. The intrinsic enzyme potency for PDE4 inhibition by L-454,560 also results in an effective blockade of LPS-induced TNFalpha formation in whole blood (IC50 = 161 nM) and is comparable to the human whole blood potency of roflumilast. The cytokine profile of inhibition of L-454,560 is mainly a Th1 profile with significant inhibition of IFNgamma and no detectable inhibition of IL-13 formation up to 1 microM. L-454,560 was also found to be efficacious in two models of airway hyper-reactivity, the ovalbumin (OVA) sensitized and challenged guinea pig and the ascaris sensitized sheep model. Furthermore, L-454560 was also effective in improving performance in the delayed matching to position (DMTP) version of the Morris watermaze, at a dose removed from that associated with potential emesis. Therefore, L-454,560 is a novel PDE4 inhibitor with an overall in vivo efficacy profile at least comparable to roflumilast and clearly superior to cilomilast.

Peripheral phosphodiesterase 4 inhibition produced by 4-[2-(3,4-Bis-difluoromethoxyphenyl)-2-[4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropan-2-yl)-phenyl]-ethyl]-3-methylpyridine-1-oxide (L-826,141) prevents experimental autoimmune encephalomyelitis

Administration of phosphodiesterase 4 (PDE4) inhibitors suppresses the pathogenesis associated with experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). In the present study, we compared the effects of rolipram and 4-[2-(3,4-bis-difluoromethoxyphenyl)-2-[4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropan-2-yl)-phenyl]-ethyl]-3-methylpyridine-1-oxide (L-826,141), a novel nonbrain penetrant PDE4 inhibitor, on the onset and severity of clinical signs in a chronic, nonrelapsing/remitting model of EAE. Both rolipram (10 mg/kg p.o.) and L-826,141 (3 mg/kg p.o.) reduced the severity of EAE relative to controls, whereas L-826,141 (3 mg/kg p.o.) also delayed disease onset. To assess whether L-826,141 prevented EAE progression after the first signs of clinical onset, rolipram (10 mg/kg p.o.) or L-826,141 (3 or 30 mg/kg p.o.) were administered 24 h after the first signs of EAE were observed. Only L-826,141 at a dose of 30 mg/kg p.o. significantly decreased the clinical severity of EAE compared with vehicle controls. Immunohistochemical detection of the neuronal activity marker Fos confirmed that L-826,141 did not reach concentrations in the central nervous system sufficient to activate central neurons. Lipopolysaccharide-induced tumor necrosis factor-alpha in whole blood and plasma concentrations of L-826,141 revealed that only the 30-mg/kg dose resulted in levels sufficient to produce a near complete inhibition of PDE4 activity in immune cells. Taken together, these results demonstrate that peripheral PDE4 inhibition, produced by L-826,141, prevents the progression of EAE after the first onset of clinical signs, and suggest that similar compounds may have clinical efficacy in the treatment of MS.

Preferential inhibition of T helper 1, but not T helper 2, cytokines in vitro by L-826,141 [4-[2-(3,4-Bisdifluromethoxyphenyl)-2-[4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropan-2-yl)-phenyl]-ethyl]3-methylpyridine-1-oxide], a potent and selective phosphodiesterase 4 inhibitor

L-826,141 [4-(2-(3,4-bis-difluromethoxyphenyl)-2-(4-(1,1,1, 3,3,3-hexafluoro-2-hydroxypropan-2-yl)-phenyl]-ethyl)-3-methylpyridine-1-oxide] is a selective and potent inhibitor of phosphodiesterase 4 (PDE4) with an IC(50) value of 0.26 to 2.4 nM for inhibition of the catalytic activity of PDE4A, B, C, and D. The cAMP elevation that can be maintained by PDE4 inhibitors attenuates the signaling cascades that lead to the production of certain cytokines. In cellular-based assays, L-826,141 transcriptionally down-regulates production of tumor necrosis factor (TNF)-alpha in peripheral blood mononuclear cell and whole blood assays with IC(50) values of 31 and 310 nM, respectively. Profiling the effect of this compound on various cytokines in the signaling cascade attenuated by cAMP elevation demonstrates that L-826,141 is also a potent inhibitor of interleukin (IL)-12, granulocyte macrophage-colony stimulating factor, and interferon (IFN)gamma (IC(50) values of 0.3-0.9 microM) as well as TNF-alpha formation. We have also shown that the PDE4 inhibitors rolipram and L-826,141 are potent inhibitors of CD3-plus CD28-stimulated IL-2 production in naive human T cells. To address the effect of PDE4 inhibitors on cytokine release from T helper (Th)1 and Th2 effector cells, we used a well characterized model in which T cells are derived from ovalbumin (323-339)-specific T cell receptor transgenic mice. L-826,141 inhibits Th0-mediated IL-2 production with an IC(35) value of 25 nM and Th1-mediated IFNgamma production with an IC(30) value of 46 nM. In contrast, L-826,141 had no significant inhibitory effect (IC(30) value > 2.5 microM) on Th2 cell-mediated IL-4 nor IL-13 production. Together, these data demonstrate that specific inhibition of PDE4 preferentially blocks the production of Th1 versus Th2 effector cytokines in vitro.

Urogenital distribution of a mouse membrane-associated prostaglandin E(2) synthase

PGE(2) plays a critical role in regulating renal function and facilitating reproduction. One of the rate-limiting biosynthetic enzymes in PGE(2) synthesis is the terminal PGE(2) synthase (PGES). In the present studies, we report the functional expression of a membrane-associated murine PGES (mPGES) and its expression in urogenital tissues. Two independent cDNA clones sharing an identical open reading frame of 459 bp and encoding a peptide of 153 amino acids, but differing in the 3'-untranslated region, were identified. Assays for enzymatic activity, using microsomes prepared from cells transfected with mPGES cDNA, showed that these cDNA sequences encode a functional protein that catalyzes the conversion of PGH(2) to PGE(2). Constitutive expression of mPGES was highest in the mouse kidney, ovary, and urinary bladder but was also expressed at lower levels in uterus and testis. Renal mPGES expression was predominantly localized to epithelia of distal tubules and medullary collecting ducts. High expression was also seen in transitional epithelial cells of bladder and ureter and in the primary and secondary follicles in the ovary. In conclusion, mPGES is constitutively expressed along the urogenital tract, where it may have important roles in normal physiology and disease.

Cloning, expression, and up-regulation of inducible rat prostaglandin e synthase during lipopolysaccharide-induced pyresis and adjuvant-induced arthritis

We have cloned and expressed the inducible form of prostaglandin (PG) E synthase from rat and characterized its regulation of expression in several tissues after in vivo lipopoylsaccharide (LPS) challenge. The rat PGE synthase is 80% identical to the human enzyme at the amino acid level and catalyzes the conversion of PGH(2) to PGE(2) when overexpressed in Chinese hamster ovary K1 (CHO-K1) cells. PGE synthase activity was measured using [(3)H]PGH(2) as substrate and stannous chloride to terminate the reaction and convert all unreacted unstable PGH(2) to PGF(2alpha) before high pressure liquid chromatography analysis. We assessed the induction of PGE synthase in tissues from Harlan Sprague-Dawley rats after LPS-induced pyresis in vivo. Rat PGE synthase was up-regulated at the mRNA level in lung, colon, brain, heart, testis, spleen, and seminal vesicles. Cyclooxygenase (COX)-2 and interleukin 1beta were also up-regulated in these tissues, although to different extents than PGE synthase. PGE synthase and COX-2 were also up-regulated to the greatest extent in a rat model of adjuvant-induced arthritis. The RNA induction of PGE synthase in lung and the adjuvant-treated paw correlated with a 3.8- and 16-fold induction of protein seen in these tissues by immunoblot analysis. Because PGE synthase is a member of the membrane-associated proteins in eicosanoid and glutathione metabolism (MAPEG) family, of which leukotriene (LT) C(4) synthase and 5-lipoxygenase-activating protein are also members, we tested the effect of LTC(4) and the 5-lipoxygenase-activating protein inhibitor MK-886 on PGE synthase activity. LTC(4) and MK-886 were found to inhibit the activity with IC(50) values of 1.2 and 3.2 microm, respectively. The results demonstrate that PGE synthase is up-regulated in vivo after LPS or adjuvant administration and suggest that this is a key enzyme involved in the formation of PGE(2) in COX-2-mediated inflammatory and pyretic responses.

Potency and selectivity of inhibition of cathepsin K, L and S by their respective propeptides

The prodomains of several cysteine proteases of the papain family have been shown to be potent inhibitors of their parent enzymes. An increased interest in cysteine proteases inhibitors has been generated with potential therapeutic targets such as cathepsin K for osteoporosis and cathepsin S for immune modulation. The propeptides of cathepsin S, L and K were expressed as glutathione S-transferase-fusion proteins in Escherichia coli. The proteins were purified on glutathione affinity columns and the glutathione S-transferase was removed by thrombin cleavage. All three propeptides were tested for inhibitor potency and found to be selective within the cathepsin L subfamily (cathepsins K, L and S) compared with cathepsin B or papain. Inhibition of cathepsin K by either procathepsin K, L or S was time-dependent and occurred by an apparent one-step mechanism. The cathepsin K propeptide had a Ki of 3.6-6.3 nM for each of the three cathepsins K, L and S. The cathepsin L propeptide was at least a 240-fold selective inhibitor of cathepsin K (Ki = 0.27 nM) and cathepsin L (Ki = 0.12 nM) compared with cathepsin S (Ki = 65 nM). Interestingly, the cathepsin S propeptide was more selective for inhibition of cathepsin L (Ki = 0.46 nM) than cathepsin S (Ki = 7.6 nM) itself or cathepsin K (Ki = 7.0 nM). This is in sharp contrast to previously published data demonstrating that the cathepsin S propeptide is equipotent for inhibition of human cathepsin S and rat and paramecium cathepsin L [Maubach, G., Schilling, K., Rommerskirch, W., Wenz, I., Schultz, J. E., Weber, E. & Wiederanders, B. (1997), Eur J. Biochem. 250, 745-750]. These results demonstrate that limited selectivity of inhibition can be measured for the procathepsins K, L and S vs. the parent enzymes, but selective inhibition vs. cathepsin B and papain was obtained.

Expression, maturation, and rhodamine-based fluorescence assay of human cathepsin K expressed in CHO cells

Cathepsin K is a cysteine protease that degrades type I human collagen during bone resorption. We have expressed the recombinant human cathepsin K in Chinese hamster ovary (CHO) cells as a pre-proenzyme and demonstrated that it is processed intracellularly to an active enzyme form and that only the proenzyme form is secreted. Immunofluorescence detection of cathepsin K in CHO cells resulted in discrete punctate distribution consistent with a lysosomal localization of the enzyme. With both extract and cell preparations of CHO cells expressing cathepsin K, [Z-Leu-Arg](2)-rhodamine was the best substrate for analyzing cathepsin K activity over background proteases. We have established a cellular-based assay to analyze cell-permeable inhibitors of cathepsin K and validated the assay with detection of intracellular versus extracellular activity, fluorescence-assisted cell sorter (FACS) analysis, and a selective cathepsin K inhibitor. The intracellular activity of cathepsin K was monitored by FACS analysis using the rhodamine substrate, which demonstrated an increased fluorescence over mock-transfected cells that was also inhibitable by (2S,3S)-trans-epoxysuccinyl-L-leucylamido-3-methylbutane ethyl ester (E64d). A selective cathepsin K inhibitor, 1, 3-bis(CBZ-Leu-NH)-2-propanone, had an IC(50) of 134 nM in the CHO/Cat K cells, which is the same potency as that measured against a purified enzyme preparation of cathepsin K. Therefore, we have established a system to evaluate intracellular cathepsin K activity and inhibition by cell-permeable inhibitors of this thiol protease.

Cloning and expression of rhesus monkey cathepsin K

Cathepsin K is a cysteine protease involved in degradation of human type I collagen and plays a primary role in bone resorption. We have cloned rhesus monkey cathepsin K by reverse transcriptase-polymerase chain reaction (RT-PCR) from rhesus ovary poly A+ RNA. The sequence for the rhesus enzyme is 98% identical to that of the human with 100% identity within the mature active form of cathepsin K. Rhesus monkey cathepsin K was transiently expressed in Chinese hamster ovary (CHO) cells and found to be secreted as the proenzyme in the culture media and 50% activated to the mature form intracellularly. The substrate specificity preference of aminomethylcoumarin and rhodamine peptide substrates was Leu > Phe > Pro in the P2 position when tested with constant arginine at P1. The enzyme activity expressed in CHO cell extracts was sensitive to inhibition by E-64 and cystatin with IC50s of 3.5 nmol/L and 13 ng/mL, respectively. The apparent second order rate constants of inactivation by E-64 were 66,000 M(-1) s(-1) and 130,000 M(-1) s(-1) for the recombinantly expressed rhesus monkey and human cathepsin K, respectively. The high similarity between the sequences and the kinetic properties of rhesus monkey and human cathepsin K establishes this monkey species as a suitable animal model for development of novel cathepsin K inhibitors as antiresorptive agents.

Cellular oxygenation of 12-hydroxyeicosatetraenoic acid and 15-hydroxyeicosatetraenoic acid by 5-lipoxygenase is stimulated by 5-lipoxygenase-activating protein

It has been proposed that 5-lipoxygenase (5-LO)-activating protein (FLAP) is an arachidonate transfer protein for leukotriene biosynthesis. Using the Spodoptera frugiperda (Sf9) insect cells, we demonstrate that FLAP causes a large stimulation (190-fold) of the conversion of 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE) to 5, 12-diHETE when co-expressed with 5-lipoxygenase. We also demonstrate that FLAP can stimulate (2-2.5-fold) the oxygenation of 15(S)-HETE by 5-LO to 5,15-diHETE. The stimulation of both 12(S)-HETE and 15(S)-HETE oxygenation by 5-LO is completely inhibitable by the FLAP inhibitor, MK-886. In order to determine which residues of FLAP are important for 12(S)-HETE and arachidonic acid utilization by 5-LO, various mutants of FLAP were co-expressed with 5-LO in Sf9 cells. The FLAP deletion mutants del 37-53, del 52-58, del 106-108, and del 148-161 and the point mutant D62N were analyzed. The D62N mutation, which reduces the binding of indole inhibitors to FLAP, had no effect on the stimulation of substrate utilization by 5-LO. In contrast to wild type FLAP, the mutant proteins del 37-53, del 106-108, and del 148-161 failed to stimulate 12(S)-HETE and arachidonic acid utilization by 5-LO. Only one of the latter three mutations (del 37-53) has been shown to abolish the binding of indole inhibitors to FLAP. These results suggest that the lipid binding site of FLAP overlaps the inhibitor binding site and occupies several regions of the protein not essential for inhibitor binding. Because FLAP can stimulate the utilization of 12(S)-HETE, 15(S)-HETE, and arachidonic acid by 5-LO, FLAP may also function as a more general lipid carrier protein for the biosynthesis of multiple oxygenation products of arachidonic acid in addition to its role in leukotriene biosynthesis.

Structural characterization of the covalent attachment of leukotriene A3 to leukotriene A4 hydrolase

Leukotriene A4 (LTA4) hydrolase catalyzes the conversion of the unstable epoxide LTA4 [5(S)-trans-5,6-oxido-11,14-cis-eicosatetraenoic acid] into proinflammatory LTB4. During the process of catalyzing this reaction, the enzyme is suicide inactivated by its substrate. In addition, LTA3, and analogue of LTA4 that lacks the C14-C15 double bond, is a potent suicide inhibitor of LTA4 hydrolase. We have synthesized [3H]LTA3 and used this ligand to demonstrate that LTA3 can covalently label LTA4 hydrolase and that this labeling is specifically competed for by bestatin and LTA4. Incubation of recombinant human LTA4 hydrolase with LTA3 followed by proteolysis (endoproteinase Lys-C) resulted in a peptide map with a single modified peptide defining the location of the LTA3 covalent attachment region. This modified 21-amino-acid peptide had a UV absorption spectrum corresponding to a conjugated triene chromophore which established conservation of this structural unit after covalent interaction of LTA3 with LTA4 hydrolase. MALDI-TOF mass spectrometric analysis of the 21-amino-acid peptide adduct revealed an abundant MH+ at m/z 2658, consistent with the predicted nominal mass of the sequenced peptide with the addition of a single LTA3 moiety. Proteolysis of LTA4 hydrolase modified with LTA3 was performed sequentially with endo-Asp-N and endo-Lys-C. The resulting peptide isolated by reverse-phase high-performance liquid chromatography was analyzed by mass spectroscopy revealing two related peptides, D371-K385 (m/z 2018.0) and D375-K385 (m/z 1577.8), both of which retained the elements of LTA3. Postsource decay of m/z 1577.8 resulted in an abundant ion at m/z 536 and an ion of lesser abundance at m/z 856 consistent with cleavage between V381 and P382 that supported assignment of the modified tyrosine residue at Y383. These results suggest nucleophilic attack of a tyrosine residue (Y383) at the conjugated triene epoxide of LTA3 resulting in a triene ether carbinol covalent adduct.

The interaction of arginine 106 of human prostaglandin G/H synthase-2 with inhibitors is not a universal component of inhibition mediated by nonsteroidal anti-inflammatory drugs

The three-dimensional cocrystal structures of ovine prostaglandin G/H synthase-1 (PGHS-1) with S-flurbiprofen and murine PGHS-2 with S-flurbiprofen and indomethacin reveal that the carboxylate acid groups of these nonsteroidal anti-inflammatory drugs (NSAIDs) form a salt bridge with the guanidinium group of Arg120 in PGHS-1 and Arg106 in PGHS-2. Mutagenesis studies confirmed that the Arg120 residue of PGHS-1 is critical for binding of substrate and inhibitors through ionic interactions of its guanidinium group with the carboxylate moieties of arachidonic acid and certain NSAIDs. We report here that the analogous R106E substitution in human PGHS-2 results in a catalytically active enzyme with a 30-fold higher Km value for arachidonic acid. Comparison of the inhibition of hPGHS-2(R106E) with wild-type hPGHS-2 by 11 structurally diverse selective and nonselective PGHS inhibitors revealed a 0-1000-fold decrease in inhibitory potency on the mutant enzyme. The loss of inhibitory potency of NSAIDs on hPGHS-2(R106E) could not be correlated with the presence or absence of a carboxylate functional group in the inhibitor, as was demonstrated previously for the PGHS-1(R120E) mutant, or with the selective or nonselective nature of the PGHS inhibitor. The decreases in the inhibitory potencies on hPGHS-2(R106E) by the carboxylate-containing NSAIDs flurbiprofen, indomethacin, meclofenamic acid, and diclofenac on hPGHS-2(R106E) were 965-, 48-, 5.5-, and 4.5-fold, respectively. The nonuniversal requirement for interaction of the carboxylate group of certain NSAIDs with the Arg106 residue in hPGHS-2 is supported by the observation that the methyl ester derivative of indomethacin was a more potent inhibitor than indomethacin on both hPGHS-2 and hPGHS-2(R106E). The greatest loss of potency for inhibition of hPGHS-2(R106E) was observed with the hPGHS-2-selective sulfonamide-containing inhibitors NS-398 and flosulide. The PGHS-2-selective inhibitor DuP697 and a desbromo-sulfonamide analogue of DuP697 displayed equivalent potency on hPGHS-2(R106E) and hPGHS-2. The change in inhibitory potency of NS-398 on hPGHS-2(R106E) was due to a difference in the kinetics of inhibition, with NS-398 displaying time-dependent inhibition of hPGHS-2 but time-independent inhibition of PGHS-2(R106E). The time-dependent inhibition of hPGHS-2 by DuP697 was not affected by the presence of the R106E mutation. We conclude that the Arg106 residue of hPGHS-2 is involved in binding arachidonic acid and certain NSAIDs, but interactions with Arg106 are not a universal requirement for inhibition by either carboxylate-containing NSAIDs or PGHS-2-selective inhibitors.

Identification and characterization of a novel microsomal enzyme with glutathione-dependent transferase and peroxidase activities

5-Lipoxygenase activating protein (FLAP), leukotriene-C4 (LTC4) synthase, and microsomal glutathione S-transferase II (microsomal GST-II) are all members of a common gene family that may also include microsomal GST-I. The present work describes the identification and characterization of a novel member of this family termed microsomal glutathione S-transferase III (microsomal GST-III). The open reading frame encodes a 16.5-kDa protein with a calculated pI of 10.2. Microsomal GST-III has 36, 27, 22, and 20% amino acid identity to microsomal GST-II, LTC4 synthase, microsomal GST-I, and FLAP, respectively. Microsomal GST-III also has a similar hydrophobicity pattern to FLAP, LTC4 synthase, and microsomal GST-I. Fluorescent in situ hybridization mapped microsomal GST-III to chromosomal localization 1q23. Like microsomal GST-II, microsomal GST-III has a wide tissue distribution (at the mRNA level) and is predominantly expressed in human heart, skeletal muscle, and adrenal cortex, and it is also found in brain, placenta, liver, and kidney tissues. Expression of microsomal GST-III mRNA was also detected in several glandular tissues such as pancreas, thyroid, testis, and ovary. In contrast, microsomal GST-III mRNA expression was very low (if any) in lung, thymus, and peripheral blood leukocytes. Microsomal GST-III protein was expressed in a baculovirus insect cell system, and microsomes from Sf9 cells containing either microsomal GST-II or microsomal GST-III were both found to possess glutathione-dependent peroxidase activity as shown by their ability to reduce 5-HPETE to 5-HETE in the presence of reduced glutathione. The apparent Km of 5-HPETE was determined to be approximately 7 microM for microsomal GST-II and 21 microM for microsomal GST-III. Microsomal GST-III was also found to catalyze the production of LTC4 from LTA4 and reduced glutathione. Based on these catalytic activities it is proposed that this novel membrane protein is a member of the microsomal glutathione S-transferase super family, which also includes microsomal GST-I, LTC4 synthase, FLAP, and microsomal GST-II.

Characterization of microsomal GST-II by western blot and identification of a novel LTC4 isomer

Protein expression of microsomal GST-II and LTC4 synthase was analyzed by Western blot. Correlation between a 17 kDa band and LTC4 formation was observed for both enzymes. The expression of microsomal GST-II was several fold more efficient than the expression of LTC4 synthase. In addition to catalyzing the biosynthesis of LTC4, microsomal GST-II also produces another product, which has been subjected to mass spectrometric analysis. This analysis demonstrates that the novel product is an isomer of LTC4.

Comparison of the cyclooxygenase-1 inhibitory properties of nonsteroidal anti-inflammatory drugs (NSAIDs) and selective COX-2 inhibitors, using sensitive microsomal and platelet assays

Two forms of cyclooxygenase (COX) activity are involved in the synthesis of prostaglandins, prostacyclins, and thromboxanes in mammalian cells. There is now convincing evidence, obtained with a number of structurally distinct inhibitors, that selective COX-2 inhibitors possess anti-inflammatory effects with an improved gastrointestinal tolerability compared with conventional nonsteroidal anti-inflammatory drugs (NSAIDs) affecting both COX-1 and COX-2. As more selective COX-2 inhibitors are being developed, assays with a high degree of sensitivity to inhibition are needed to compare the relative effects of compounds on COX-1 activity. In the present report, we describe a sensitive assay for the inhibition of human COX-1 based on the production of prostaglandin E2 by microsomes from U937 cells incubated with a subsaturating concentration of arachidonic acid. More than 45 NSAIDs and selective COX-2 inhibitors were tested in this assay. IC50 values ranged from 1 nM for flunixin and flurbiprofen to about 200-500 microM for salicylate and acetaminophen. Potent and nonselective NSAIDs such as sulindac sulfide, diclofenac, and indomethacin showed IC50 values of < 20 nM. Among the compounds that have been reported to show selectivity for COX-2, the rank order of potency against COX-1 was DuP 697 > SC-58451 > celecoxib > nimesulide-meloxicam-piroxicam-NS-398-RS-57067 > SC-57666 > SC-58125 > flosulide > etodolac > L-745,337 > DFU-T-614, with IC50 values ranging from 7 nM to 17 microM. A good correlation was obtained between the IC50 values for the inhibition of microsomal COX-1 and both the inhibition of TXB2 production by Ca2+ ionophore challenged platelets and the inhibition of prostaglandin E2 production by CHO cells stably expressing human COX-1. However, the microsomal assay was more sensitive to inhibition than cell-based assays and allowed the detection of inhibitory effects on COX-1 for all NSAIDs and selective COX-2 inhibitors examined with discrimination of their potency under conditions of limited availability of arachidonic acid.

Biochemical and pharmacological profile of a tetrasubstituted furanone as a highly selective COX-2 inhibitor

1. DFU (5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulphonyl)phenyl-2(5H)-furan one) was identified as a novel orally active and highly selective cyclo-oxygenase-2 (COX-2) inhibitor. 2. In CHO cells stably transfected with human COX isozymes, DFU inhibited the arachidonic acid-dependent production of prostaglandin E2 (PGE2) with at least a 1,000 fold selectivity for COX-2 (IC50 = 41 +/- 14 nM) over COX-1 (IC50 > 50 microM). Indomethacin was a potent inhibitor of both COX-1 (IC50 = 18 +/- 3 nM) and COX-2 (IC50 = 26 +/- 6 nM) under the same assay conditions. The large increase in selectivity of DFU over indomethacin was also observed in COX-1 mediated production of thromboxane B2 (TXB2) by Ca2+ ionophore-challenged human platelets (IC50 > 50 microM and 4.1 +/- 1.7 nM, respectively). 3. DFU caused a time-dependent inhibition of purified recombinant human COX-2 with a Ki, value of 140 +/- 68 microM for the initial reversible binding to enzyme and a kappa 2 value of 0.11 +/- 0.06 s-1 for the first order rate constant for formation of a tightly bound enzyme-inhibitor complex. Comparable values of 62 +/- 26 microM and 0.06 +/- 0.01 s-1, respectively, were obtained for indomethacin. The enzyme-inhibitor complex was found to have a 1:1 stoichiometry and to dissociate only very slowly (t1/2 = 1-3 h) with recovery of intact inhibitor and active enzyme. The time-dependent inhibition by DFU was decreased by co-incubation with arachidonic acid under non-turnover conditions, consistent with reversible competitive inhibition at the COX active site. 4. Inhibition of purified recombinant human COX-1 by DFU was very weak and observed only at low concentrations of substrate (IC50 = 63 +/- 5 microM at 0.1 microM arachidonic acid). In contrast to COX-2, inhibition was time-independent and rapidly reversible. These data are consistent with a reversible competitive inhibition of COX-1. 5. DFU inhibited lipopolysaccharide (LPS)-induced PGE2 production (COX-2) in a human whole blood assay with a potency (IC50 = 0.28 +/- 0.04 microM) similar to indomethacin (IC50 = 0.68 +/- 0.17 microM). In contrast, DFU was at least 500 times less potent (IC50 > 97 microM) than indomethacin at inhibiting coagulation-induced TXB2 production (COX-1) (IC50 = 0.19 +/- 0.02 microM). 6. In a sensitive assay with U937 cell microsomes at a low arachidonic acid concentration (0.1 microM), DFU inhibited COX-1 with an IC50 value of 13 +/- 2 microM as compared to 20 +/- 1 nM for indomethacin. CGP 28238, etodolac and SC-58125 were about 10 times more potent inhibitors of COX-1 than DFU. The order of potency of various inhibitors was diclofenac > indomethacin approximately naproxen > nimesulide approximately meloxicam approximately piroxicam > NS-398 approximately SC-57666 > SC-58125 > CGP 28238 approximately etodolac > L-745,337 > DFU. 7. DFU inhibited dose-dependently both the carrageenan-induced rat paw oedema (ED50 of 1.1 mg kg-1 vs 2.0 mg kg-1 for indomethacin) and hyperalgesia (ED50 of 0.95 mg kg-1 vs 1.5 mg kg-1 for indomethacin). The compound was also effective at reversing LPS-induced pyrexia in rats (ED50 = 0.76 mg kg-1 vs 1.1 mg kg-1 for indomethacin). 8. In a sensitive model in which 51Cr faecal excretion was used to assess the integrity of the gastrointestinal tract in rats, no significant effect was detected after oral administration of DFU (100 mg kg-1, b.i.d.) for 5 days, whereas chromium leakage was observed with lower doses of diclofenac (3 mg kg-1), meloxicam (3 mg kg-1) or etodolac (10-30 mg kg-1). A 5 day administration of DFU in squirrel monkeys (100 mg kg-1) did not affect chromium leakage in contrast to diclofenac (1 mg kg-1) or naproxen (5 mg kg-1). 9. The results indicate that COX-1 inhibitory effects can be detected for all selective COX-2 inhibitors tested by use of a sensitive assay at low substrate concentration. The novel inhibitor DFU shows the lowest inhibitory potency against COX-1, a consistent high selectivity of inhibition of COX-2 over COX-1 (>300 fold) with enzyme, whole cell and whole blood assays, with no detectable loss of integrity of the gastrointestinal tract at doses >200 fold higher than efficacious doses in models of inflammation, pyresis and hyperalgesia. These results provide further evidence that prostanoids derived from COX-1 activity are not important in acute inflammatory responses and that a high therapeutic index of anti-inflammatory effect to gastropathy can be achieved with a selective COX-2 inhibitor.

Conversion of prostaglandin G/H synthase-1 into an enzyme sensitive to PGHS-2-selective inhibitors by a double His513 --> Arg and Ile523 --> val mutation

Modeling of the active site of prostaglandin G/H synthase-2 (PGHS-2) onto PGHS-1 utilizing the known crystal structure of PGHS-1 shows that the only residues impinging directly on the active site that were not conserved in the two enzymes are His513 and Ile523 of PGHS-1 (Arg499 and Val509 of PGHS-2). These residues of human PGHS-1 were each mutated to the corresponding PGHS-2 residues (His513 --> Arg and Ile523 --> Val) and a double mutant (His513 --> Arg,Ile523 --> Val) containing both residues was also constructed. The mutant enzyme forms were expressed in COS-7 cells, and their properties were compared with those of the normal isoforms using microsomal membranes. The mutated enzyme forms all had apparent Km values within 1.4-fold that of the wild type enzyme, and the specific activity of the mutants were within 2-fold of that of PGHS-1. DuP697, NS-398, DFU, and SC-58125 are selective PGHS-2 inhibitors that act as time-dependent inhibitors of PGHS-2 and rapidly reversible competitive inhibitors of PGHS-1. The single Ile523 --> Val mutation increased the sensitivity to each of these selective inhibitors with most of the effect detected using instantaneous inhibition assays, except for DuP697, whose potency was further increased by preincubation with the enzyme. The double PGHS-1 His513 --> Arg, Ile523 --> Val mutant became more sensitive to inhibition by NS-398 and DFU than the single IV mutant, and time-dependent inhibition was observed. In contrast, the single HR mutation did not increase the sensitivity to inhibition by the selective PGHS-2 inhibitors. The potency of a selective PGHS-1 inhibitor, L-745,296, was decreased 5- and 13-fold in the HR and HR-IV mutants, respectively. All the results indicate that mutations of His513 and Ile523 residues of PGHS-1 can strongly increase sensitivity to selective PGHS-2 inhibition and restore time-dependent inhibition. They also suggest that the corresponding Arg499 and Val509 residues of PGHS-2 are essential determinants in differentiating between the interaction of nonselective NSAIDs and selective PGHS-2 inhibitors and their mechanism of action.

Altered sensitivity of aspirin-acetylated prostaglandin G/H synthase-2 to inhibition by nonsteroidal anti-inflammatory drugs

Aspirin (ASA) acetylates Ser516 of prostaglandin G/H synthase-2 (PGHS-2) resulting in a modified enzyme that converts arachidonic acid to 15(R)-hydroxy-eicosatetraeroic acid [15(R)-HETE]. ASA has pharmacological benefits that may not all be limited to inhibition of prostaglandin synthesis, and this study was initiated to further investigate the properties of ASA-acetylated PGHS-2 and of the mutation of Ser516 to methionine, which mimics ASA acetylation. Both the S516M mutant and ASA-acetylated form of PGHS-2 (ASA-PGHS-2) synthesize 15(R)-HETE and have apparent K(m) values for arachidonic acid within 10-fold of the apparent K(m) value for untreated PGHS-2. The time courses of turnover-dependent inactivation were similar for reactions catalyzed by PGHS-2 and ASA-PGHS-2, whereas the PGHS-2(S516M) showed a decrease in both the initial rate of 15-HETE production and rate of enzyme inactivation. The production of 15-HETE by modified PGHS-2 was sensitive to inhibition by most nonsteroidal anti-inflammatory drugs (NSAIDs), including selective PGHS-2 inhibitors. As observed for the cyclooxygenase activity of PGHS-2, the inhibition of 15-HETE production by indomethacin was time-dependent for both ASA-PGHS-2 and PGHS-2(S516M). However, two potent, structurally related NSAIDs, diclofenac and meclofenamic acid, do not inhibit either ASA-PGHS-2 or the PGHS-2(S516M) mutant. These results demonstrate that the sensitivity to inhibition by NSAIDs of the 15-HETE production by ASA-treated PGHS-2 is different than that of prostaglandin production by PGHS-2 and that Ser516 plays an important role in the interaction with fenamate inhibitors. The results also indicate that the conversion of arachidonic acid to 15-HETE by ASA-PGHS-2 is an efficient process providing a unique mechanism among NSAIDs that will not lead to arachidonic acid accumulation or shunting to other biosynthetic pathways.

Identification and characterization of a novel human microsomal glutathione S-transferase with leukotriene C4 synthase activity and significant sequence identity to 5-lipoxygenase-activating protein and leukotriene C4 synthase

5-Lipoxygenase-activating protein (FLAP) and leukotriene C4 (LTC4) synthase, two proteins involved in leukotriene biosynthesis, have been demonstrated to be 31% identical at the amino acid level. We have recently identified and characterized a novel member of the FLAP/LTC4 synthase gene family termed microsomal glutathione S-transferase II (microsomal GST-II). The open reading frame encodes a 16.6-kDa protein with a calculated pI of 10.4. Microsomal GST-II has 33% amino acid identity to FLAP, 44% amino acid identity to LTC4 synthase, and 11% amino acid identity to the previously characterized human microsomal GST (microsomal GST-I). Microsomal GST-II also has a similar hydrophobicity pattern to FLAP, LTC4 synthase, and microsomal GST-I. Fluorescent in situ hybridization mapped microsomal GST-II to chromosomal localization 4q28-31. Microsomal GST-II has a wide tissue distribution (at the mRNA level) and was specifically expressed in human liver, spleen, skeletal muscle, heart, adrenals, pancreas, prostate, testis, fetal liver, and fetal spleen. In contrast, microsomal GST-II mRNA expression was very low (when present) in lung, brain, placenta, and bone marrow. This differs from FLAP mRNA, which was detected in lung, various organs of the immune system, and peripheral blood leukocytes, and LTC4 synthase mRNA, which could not be detected in any tissues by Northern blot analysis. Microsomal GST-II and LTC4 synthase were expressed in a baculovirus insect cell system, and microsomes from Sf9 cells containing microsomal GST-II or LTC4 synthase were both found to catalyze the production of LTC4 from LTA4 and reduced glutathione. Microsomal GST-II also catalyzed the formation of another product, displaying a conjugated triene UV absorption spectra with a maximum at 283 nm, suggesting less catalytic stereospecificity compared with LTC4 synthase. Also, the apparent Km for LTA4 was higher for microsomal GST-II (41 microM) than LTC4 synthase (7 microM). In addition, unlike LTC4 synthase, microsomal GST-II was able to catalyze the conjugation of 1-chloro-2, 4-dinitrobenzene with reduced glutathione. Therefore, it is proposed that this novel membrane protein is a member of the microsomal glutathione S-transferase family, also including LTC4 synthase, with significant sequence identities to both LTC4 synthase and FLAP.

Colocalization of cytosolic phospholipase A2, 5-lipoxygenase, and 5-lipoxygenase-activating protein at the nuclear membrane of A23187-stimulated human neutrophils

The distribution of cytosolic phospholipase A2 (cPLA2), arachidonate 5-lipoxygenase, and 5-lipoxygenase-activating protein (5-LAP) was investigated in subcellular fractions of human neutrophils disrupted by three techniques. As determined by immunoblot analysis, the bulk of cPLA2 and 5-lipoxygenase was detected in cytosolic fractions of unstimulated neutrophils disrupted by sonication or cavitation. After cell stimulation with the calcium ionophore A23187, both proteins accumulated primarily in nuclei-containing fractions; this accumulation was accompanied by a loss of these enzymes from cytosolic fractions. Further resolution of nuclear fractions revealed that 5-lipoxygenase and cPLA2 were localized in a fraction that contained nuclear membranes. In comparison, 5-LAP was localized to the nuclear-membrane fraction of resting and activated neutrophils, as determined by immunoblotting and photoaffinity labeling. In agreement with the immunoblot data, A23187 stimulation markedly enhanced 5-lipoxygenase enzymatic activity in the nuclear-membrane fraction, which was accompanied by decreased cytosolic 5-lipoxygenase activity. Similarly, neutrophil activation caused increased phosphorylation of cPLA2, a process that is known to result in enhanced catalytic activity. Our data demonstrate that in activated human neutrophils, the key proteins involved in leukotriene synthesis colocalize at the nuclear membrane, in a catalytically active state.

Arginine 120 of prostaglandin G/H synthase-1 is required for the inhibition by nonsteroidal anti-inflammatory drugs containing a carboxylic acid moiety

The therapeutic action of nonsteroidal anti-inflammatory drugs (NSAIDs) is exerted through the inhibition of prostaglandin G/H synthase (PGHS), which is expressed as two isoenzymes, termed PGHS-1 and PGHS-2. From the crystal structure of sheep PGHS-1, it has been proposed that the carboxylic acid group of flurbiprofen is located in a favorable position for interacting with the arginine 120 residue of PGHS-1 (Picot, D., Loll, P. J., and Garavito, R. M. (1994) Nature 367, 243-249). Mutation of this Arg120 residue to Glu was performed and expressed in COS-7 cells using a vaccinia virus expression system. Comparison of microsomal enzyme preparations show that the mutation results in a 20-fold reduction in the specific activity of PGHS-1 and in a 100-fold increase in the apparent Km for arachidonic acid. Indomethacin, flurbiprofen, and ketoprofen, inhibitors of PGHS activity containing a free carboxylic acid group, do not exhibit any inhibitory effects against the activity of PGHS-1(Arg120-->Glu). Diclofenac and meclofenamic acid, other NSAIDs containing a free carboxylic acid group, were 50-100-fold less potent inhibitors of the activity of the mutant as compared with the wild type PGHS. In contrast, the nonacid PGHS inhibitors, 5-bromo-2-(4-fluorophenyl)-3-(4-methylsulfonyl)thiophene (DuP697) and a desbromo-sulfonamide analogue of DuP697 (L-746,483), were both more potent inhibitors of PGHS-1(Arg120-->Glu) than of the wild tyupe PGHS-1. Inhibition of PGHS-1(Arg120-->Glu) was time-dependent for diclofenac and time-independent for DuP697, as observed for the wild type enzyme, indicating that the mutation does not alter the basic mechanism of inhibition. Aspirin is an acid NSAID that inhibits PGHS-1 through a unique covalent acetylation of the enzyme and also showed a reduced rate of inactivation of the mutated enzyme. These data provide biochemical evidence of the importance of the Arg120 residue in PGHS-1 for interaction with arachidonic acid and NSAIDs containing a free carboxylic acid moiety.

Cloning and characterization of the human leukotriene A4 hydrolase gene

The human gene encoding the bifunctional aminopeptidase and epoxide hydrolase enzyme, leukotriene A4 hydrolase (LTA4 hydrolase) has been cloned from a placental lambda phage genomic library. The gene is greater than 35 kbp and contains 19 exons ranging in size over 24-312 bp. The introns range in size over 0.26-5.7 kbp. The essential zinc-binding histidine residues and glutamate residue, which delineate the zinc-binding domain required for both enzyme activities of LTA4 hydrolase, are divided between exons 10 and 11. The LTA4 hydrolase gene was localized to chromosome 12q22 utilizing fluorescence in situ hybridization. Based on the chromosome localization and genomic DNA analysis, LTA4 hydrolase was determined to be a single-copy gene. Primer-extension analysis demonstrated that the transcription initiation site of LTA4 hydrolase mRNA is 151 nucleotides upstream of the initiator ATG. Approximately 4 kbp of 5'-flanking region of the LTA4 hydrolase gene has been obtained and sequencing of 1.4 kb of this 5'-flanking region demonstrated several transcription-factor consensus sequences, including a phorbol-ester-response element (AP2) and two xenobiotic-response elements. The cloning and characterization of the human gene for LTA4 hydrolase provides a basis for further insight into transcriptional regulation of this bifunctional enzyme and its role in various inflammatory processes.

Expression of prostaglandin G/H synthase-1 and -2 protein in human colon cancer

Prostaglandin G/H synthase (PGHS), a key enzyme leading to the formation of prostaglandins, is the target of nonsteroidal antiinflammatory drugs. Two forms of the enzyme have been identified, PGHS-1 and PGHS-2. Epidemiological evidence has suggested that aspirin and other nonsteroidal antiinflammatory drugs may reduce the risk of colorectal cancer. We examined by immunoblot analyses the expression of human PGHS-1 and PGHS-2 protein in 25 matched colon cancer and nontumor tissues, 4 premalignant polyps, 5 control colon tissues from noncancer patients, and 3 matched normal and cancerous breast tissue samples. PGHS-1 was detected in all normal and tumor tissue. In contrast, PGHS-2 was not detected in 23 of 25 normal colon tissues but was detected in 19 of 25 colon tumors. PGHS-2 protein was not observed in four human premalignant polyp samples, control colon from noncancer patients, or matched normal or cancerous breast tissues. These results suggest that the beneficial effects of nonsteroidal antiinflammatory drugs in colon cancer may be mediated by inhibition of PGHS-2.

Selective inhibitors of COX-2

The main target of non-steroidal anti-inflammatory drugs (NSAIDs) is prostaglandin G/H synthase (PGHS), also known as cyclooxygenase (COX), which exists as two isoforms. In order to evaluate the contributions of PGHS isoforms to physiological and pathological conditions and their sensitivity to inhibition by non-steroidal anti-inflammatory drugs, we have established high level expression systems of recombinant human PGHS isoforms. The inducible form of PGHS, termed PGHS-2, has been purified and characterized with respect to substrate specificity, product formation, enzymatic activity, glycosylation, heme content, quaternary structure, and modification by aspirin. Pharmacological profiles of the recombinant PGHS isoforms indicate that conventional NSAIDs show little selectivity for either enzyme, however, the recently described NSAID, NS-398, exhibits a high degree of specificity for PGHS-2 through a time dependent mechanism.

Mutation of serine-516 in human prostaglandin G/H synthase-2 to methionine or aspirin acetylation of this residue stimulates 15-R-HETE synthesis

Prostaglandin G/H synthase (PGHS) is a key enzyme in cellular prostaglandin (PG) synthesis and is the target of non-steroidal anti-inflammatory agents. PGHS occurs in two isoforms, termed PGHS-1 and PGHS-2. These isoforms differ in several respects, including their enzymatic activity following acetylation by aspirin. While PG synthesis by both isoforms is inhibited by aspirin, 15-R-hydroxyeicosatetraenoic acid (15-R-HETE) synthesis by PGHS-2, but not PGHS-1, is stimulated by preincubation with aspirin. We have mutated the putative aspirin acetylation site of hPGHS-2, and expressed the mutants in COS-7 cells using recombinant vaccinia virus. Enzyme activity and inhibitor sensitivity studies provide evidence that Ser516 is the aspirin acetylation site of human PGHS-2 and that substitution of a methionine residue at this position can mimic the effects of aspirin acetylation on enzyme activity.

Overexpression of human prostaglandin G/H synthase-1 and -2 by recombinant vaccinia virus: inhibition by nonsteroidal anti-inflammatory drugs and biosynthesis of 15-hydroxyeicosatetraenoic acid

Human prostaglandin G/H synthase (hPGHS)-1 and hPGHS-2, key enzymes in the formation of prostanoids from arachidonic acid, were expressed at high levels in COS-7 cells using a T7 RNA polymerase/vaccinia virus expression system. The open reading frame of hPGHS-2 cloned into vaccinia virus without its natural 5' and 3' untranslated regions directed only low levels of hPGHS-2 enzyme activity in COS-7 cells. High-level hPGHS-2 expression was achieved by appending the 3' untranslated region of hPGHS-1 to the hPGHS-2 open reading frame, with subsequent expression of the hybrid mRNA using vaccinia virus. Enzymatically active recombinant hPGHS-1 and hPGHS-2 were present as glycosylated proteins in the microsomal fraction prepared from infected cells, whereas recombinant hPGHS-1 and hPGHS-2 prepared from the microsomal fraction of cells treated with tunicamycin, an inhibitor of N-linked glycosylation, were enzymatically inactive. The major prostanoid products formed by microsomes from COS-7 cells containing either recombinant hPGHS-1 or hPGHS-2 after incubation with arachidonic acid were prostaglandin D2 and E2, with lower levels of prostaglandin F2 alpha and 6-keto-prostaglandin F1 alpha. A range of potencies were observed for various nonsteroidal anti-inflammatory drugs as inhibitors of prostaglandin E2 synthesis by hPGHS-1 and hPGHS-2. Recombinant hPGHS-1 and hPGHS-2 both produced 15- and 11-hydroxyeicosatetraenoic acid (HETE) from arachidonic acid, with 15-HETE production by hPGHS-2 being stimulated 5-fold by preincubation with aspirin. Chiral phase high performance liquid chromatography analysis showed that aspirin-treated hPGHS-2 produced 15(R)-HETE, with no detectable 15(S)-HETE.

The binding of leukotriene biosynthesis inhibitors to site-directed mutants of human 5-lipoxygenase-activating protein

Site-directed mutagenesis was used to develop deletion and point mutants of human 5-lipoxygenase-activating protein (FLAP), which were then expressed in COS-7 cells. Membrane preparations from these cells were analyzed in a radioligand binding assay. Binding of leukotriene biosynthesis inhibitors to FLAP mutants containing deletions of 2 to 6 amino acids within the region from residue 48-61 was undetectable. This finding is consistent with previous studies which suggest that residues amino-terminal to the proposed second transmembrane of FLAP are critical for inhibitor binding. The present study also defines residues of FLAP a) amino-terminal to residue 48, b) between the proposed second and third transmembrane regions and c) in the C-terminal region of the protein which are not involved in inhibitor binding.

Coupling of recombinant 5-lipoxygenase and leukotriene A4 hydrolase activities and transcellular metabolism of leukotriene A4 in Sf9 insect cells

High-level expression of human leukotriene (LT) A4 hydrolase has been established in Sf9 insect cells using the recombinant baculovirus system. LTA4 hydrolase activity in this system is at least 50-fold higher than previously achieved in a bacterial cell system. Recombinant viral human LTA4 hydrolase (rvHLTA4h) was used for coinfection studies with recombinant viral 5-lipoxygenase (rvH5LO). When Sf9 cells expressing 5-lipoxygenase are incubated in the presence of A23187 and arachidonic acid, (5S)-hydroperoxy-6-trans-8,11,14-cis-eicosatetraenoic acid 5-H(P)ETE and LTA4 are synthesized in a ratio of 5:1 for 5-H(P)ETE/LT. Coexpression of 5-lipoxygenase and LTA4 hydrolase in these insect cells results in the synthesis of 5-H(P)ETE, LTA4 and in addition LTB4, and the ratio shifts to 2:1 for 5-H(P)ETE/LT. The production of enzymically formed LTB4 after addition of arachidonic acid to the Sf9 cells coinfected with LTA4 hydrolase and 5-lipoxygenase is the first demonstration of channeling of arachidonic acid to LTB4 in an engineered intact cell system. This delineates a novel biological system to synthesize significant amounts of the potent chemotactic agent, LTB4. Studies in which Sf9 cells infected with rvH5LO were incubated with Sf9 cells infected with rvHLTA4h resulted in export of LTA4 from the rvH5LO cells and transcellular metabolism of LTA4 to LTB4 in the rvHLTA4h Sf9cells.

5-Lipoxygenase activity in the human pancreas

Low levels of 5-lipoxygenase (5-LO), the first committed enzyme in the synthesis of leukotrienes (LTs), have been reported in the porcine pancreas. We have quantitated 5-LO activity in subcellular fractions of pancreas samples from three human donors. 5-LO activity was detectable in all samples, although enzyme activity was lower than in human leukocytes. 5-LO in human pancreas samples displayed highest specific activity in membrane fractions, and did not require arachidonic acid (AA) addition for activity. These unusual characteristics of pancreatic 5-LO appear to be due, at least in part, to the presence of unesterified AA in the pancreas samples. Western blot analysis demonstrated that the human pancreas contains low levels of 5-lipoxygenase-activating protein (FLAP) in addition to 5-LO.

Leukotriene synthesis in U937 cells expressing recombinant 5-lipoxygenase

The U937 human promyelocytic cell line does not express 5-lipoxygenase, but does express 5-lipoxygenase-activating protein (FLAP). U937 cells do not synthesize leukotrienes after stimulation by calcium ionophore A23187. Dimethyl sulfoxide (DMSO) differentiation of U937 cells, towards a more mature monocyte-macrophage lineage, induces the expression of FLAP but not 5-lipoxygenase. These DMSO-differentiated U937 cells also lack the ability to synthesize leukotrienes. We infected viral RNA coding for 5-lipoxygenase into U937 cells using a retroviral vector and measured the synthesis of 5-lipoxygenase, FLAP, leukotrienes and 5-hydroxyeicosatetraenoic acid (5-HETE) by these cells after stimulation with A23187. Undifferentiated U937 cells infected with 5-lipoxygenase RNA expressed 5-lipoxygenase and FLAP but neither leukotrienes nor 5-HETE were detected after these cells were stimulated with A23187. Exposure of the 5-lipoxygenase-infected U937 cells to DMSO increased the expression of 5-lipoxygenase and FLAP, and these cells produced leukotrienes and 5-HETE in response to A23187. The synthesis of these products was inhibited by MK-886, a compound which specifically binds to FLAP.

5-lipoxygenase-activating protein is an arachidonate binding protein

5-Lipoxygenase-activating protein (FLAP) is an 18-kDa integral membrane protein which is essential for cellular leukotriene (LT) synthesis, and is the target of LT biosynthesis inhibitors. However, the mechanism by which FLAP activates 5-LO has not been determined. We have expressed high levels of human FLAP in Spodoptera frugiperda (Sf9) insect cells infected with recombinant baculovirus, and used this system to demonstrate that FLAP specifically binds [125I]L-739,059, a novel photoaffinity analog of arachidonic acid. This binding is inhibited by both arachidonic acid and MK-886, an LT biosynthesis inhibitor which specifically interacts with FLAP. These studies suggest that FLAP may activate 5-LO by specifically binding arachidonic acid and transferring this substrate to the enzyme.

Amino acid residues of 5-lipoxygenase-activating protein critical for the binding of leukotriene biosynthesis inhibitors

5-Lipoxygenase-activating protein (FLAP) plays an essential role in cellular leukotriene (LT) synthesis and represents the target of three classes of LT biosynthesis inhibitors. We have taken three approaches to localize regions of FLAP involved in the binding of these inhibitors. A comparison of the amino acid sequences of FLAP from eight mammalian species identifies regions of the protein which are highly conserved and consequently may be involved in functional and inhibitor binding properties of the protein. Conversely, amino acids not conserved amongst these species are unlikely to play an essential role in inhibitor binding. Immunoprecipitation of peptide fragments of FLAP cross-linked to photoaffinity analogues of LT biosynthesis inhibitors following site-specific peptide cleavage indicates that the inhibitor attachment site is amino-terminal to 72Trp. Taken together, the cross-species analysis and photoaffinity labelling studies suggest a region within the first hydrophilic loop of FLAP which may be important for inhibitor binding. Site-directed mutagenesis of human FLAP followed by the analysis of FLAP mutants in a radioligand binding assay was used to more accurately define critical amino acid residues within this region. Mutagenesis studies reveal that mutants containing deletions of amino acids in regions of FLAP not conserved between species retain the ability to specifically bind inhibitors. Furthermore, mutants containing deletions in a highly conserved region of the protein (residues 42-61) do not bind inhibitors. These studies have therefore localized specific amino acids of FLAP which are essential for inhibitor binding. The roles that these amino acids play in inhibitor binding and may play in 5-LO activation is under investigation.

Cross-species comparison of 5-lipoxygenase-activating protein

To identify regions of 5-lipoxygenase-activating protein (FLAP) important for the function of the protein and the binding of leukotriene biosynthesis inhibitors, we performed a cross-species analysis of FLAP. FLAP from all 10 mammalian species analyzed (human, monkey, horse, pig, cow, sheep, rabbit, dog, rat, and mouse) were immunologically cross-reactive and specifically bound leukotriene biosynthesis inhibitors with high affinity. Using the polymerase chain reaction, cDNA clones for FLAP from six species (monkey, horse, pig, sheep, rabbit, and mouse) were isolated and sequenced. The deduced amino acid sequences of FLAP show a high degree of identity to each other and to the published sequences for human and rat FLAP. Two regions of the protein are almost totally conserved among all of the species analyzed. This suggests that these regions have functional significance and may be involved in inhibitor binding.

Identification of amino acid residues of 5-lipoxygenase-activating protein essential for the binding of leukotriene biosynthesis inhibitors

5-Lipoxygenase-activating protein (FLAP) is specifically labeled by [125I]L-669,083 and [125I]L-691,678, photoaffinity analogues of two classes of potent leukotriene biosynthesis inhibitors. Because human FLAP contains only a single tryptophan residue at position 72 and two internal methionine residues at positions 89 and 125, we have used reagents that specifically cleave at these residues, in conjunction with antipeptide antisera, to localize the site of attachment of the photoaffinity ligands. Immunoprecipitation of specifically labeled peptide fragments after digestion of photoaffinity-labeled FLAP by iodosobenzoic acid at 72Trp demonstrates that the inhibitors bind to FLAP amino-terminal to this residue. This finding is consistent with similar immunoprecipitation studies after digestion at methionine residues using cyanogen bromide. These findings localize the site of attachment of the inhibitors to a region of FLAP that includes the hydrophilic loop between the proposed first and second transmembrane regions. Based on these findings, site-directed mutagenesis of human FLAP was performed to define key amino acids involved in inhibitor binding. Using a radioligand binding assay, analysis of mutants of human FLAP expressed in COS-7 cells demonstrates that a number of residues in the amino-terminal half of the first hydrophilic loop of the protein can be deleted without significantly affecting inhibitor binding. In contrast, no inhibitor binding was detectable with mutants in which amino acid residues in the carboxyl-terminal half of this loop were deleted. Furthermore, a point mutation of 62Asp to asparagine results in a mutant with dramatically reduced affinity for inhibitors. This loss of affinity was not displayed by a mutant in which 62Asp was mutated to a glutamate residue, suggesting that a negative charge associated with residue 62 may be critical for inhibitor binding. The roles that amino acid residues in the carboxyl-terminal half of the first hydrophilic loop of FLAP may play in the binding of leukotriene biosynthesis inhibitors are currently under investigation.

Characterization of a 5-lipoxygenase-activating protein binding assay: correlation of affinity for 5-lipoxygenase-activating protein with leukotriene synthesis inhibition

A binding assay has been developed to measure the affinity of leukotriene synthesis inhibitors for 5-lipoxygenase-activating protein (FLAP), using human leukocyte membranes as the source of FLAP and a radioiodinated leukotriene synthesis inhibitor, 125I-L-691,831, as ligand. Linearity of specific binding of radiolabeled ligand was demonstrated with increasing protein and ligand concentrations. Saturation analysis of radioligand binding showed a Kd of 6 nM and a Bmax that, depending on the membrane preparation, varied between 8 and 53 pmol/mg of protein. An excellent correlation was shown between affinity for FLAP in the binding assay and inhibition of leukotriene synthesis in human polymorphonuclear leukocytes for compounds from two structurally distinct classes, namely indoles and quinolines. A large number of membrane-active compounds did not compete with 125I-L-691,831 binding to FLAP. In addition, direct 5-lipoxygenase inhibitors and a selection of eicosanoids were unable to compete for FLAP binding. This study validates a selective binding assay for leukotriene synthesis inhibitors whose protein target is FLAP.

5-Lipoxygenase-activating protein is the target of a novel hybrid of two classes of leukotriene biosynthesis inhibitors

An 18-kDa leukocyte membrane protein, termed 5-lipoxygenase-activating protein (FLAP), has recently been shown to be the target of two structurally distinct classes of leukotriene biosynthesis inhibitors. These classes of inhibitors are based on indole and quinoline structures and are represented by MK-886 and L-674,573, respectively. A novel class of hybrid structure based on the indole and quinoline classes of inhibitors, termed quindoles, has recently been developed. These compounds, exemplified by L-689,037, are potent inhibitors of leukotriene biosynthesis, both in vitro and in vivo. In the present study, we have developed and characterized a potent radioiodinated photoaffinity analogue of L-689,037, termed [125I]L-691,678. This compound was used in immunoprecipitation studies with FLAP antisera to show that the quindole series of leukotriene biosynthesis inhibitors interact directly with FLAP. In addition, we show that MK-886, L-674,573, and L-689,037 specifically compete, in a concentration-dependent manner, with both [125I]L-691,678 and [125I]L-669,083, a photoaffinity analogue of MK-886, for binding to FLAP. These results suggest that these three classes of leukotriene biosynthesis inhibitors share a common binding site on FLAP, providing further evidence that FLAP represents a suitable target for structurally diverse classes of leukotriene biosynthesis inhibitors.

Social provisions in adulthood: concept and measurement in close relationships

Social gerontologists are increasingly concerned about examining the nature of close relationships among the elderly. Theoretically grounded and empirically validated instruments are needed to advance research in this area. We analyzed the psychometric properties of the Social Provisions Scale using data from a probability sample of 494 community residents aged 65 or older. The theoretical foundation of this scale is Weiss's delineation of social support functions of close relationships. Confirmatory factor analysis revealed a pattern in the data that corresponds to the theoretical definition of relational provisions: Factor 1 was Intimacy; Factor 2 was Social Integration; Factor 3 was Reassurance of Worth; and Factor 4 was Opportunity for Nurturance. Alphas for the four scales ranged from .83 to .94. Convergent validity was supported by significant correlations between the Social Provisions Scale (SPS) and respondent's morale, frequency of contact with friends, feelings of closeness with an adult child, relationship control, and relationship conflict. Discriminant validity was supported by nonsignificant correlations between the SPS and the Eysenck Lie Scale.