The diversity of naturally produced organohalogens

Directed biosynthesis of phytotoxic alkaloids in the cyanobacterium Nostoc 78-12A

Nostocarboline, a chlorinated and N-methylated carbolinium alkaloid, displays potent and selective inhibition of photoautotrophic organisms as well as the malaria parasite Plasmodium falciparum, while showing very low toxicity to bacterial and fungal pathogens, rat myoblasts and crustaceans. New derivatives of nostocarboline incorporating Br, F or methyl substituents have been obtained through precursor-directed biosynthesis in Nostoc 78-12A (identical to Nostoc sp. ATCC 43238) by feeding this cyanobacterium with differently substituted tryptophan derivatives or 6-Br-norharmane (eudistomin N). These experiments substantiate the biosynthetic hypothesis and validate the inherent flexibility of the corresponding enzymes for metabolic engineering. The new derivatives inhibit the growth of the toxic-bloom-forming cyanobacterium Microcystis aeruginosa PCC 7806 above 1 microM. The mode of action of nostocarboline was investigated by using chlorophyll-a fluorescence imaging, and it was demonstrated that a decrease in photosynthesis precedes cell death, thus establishing the phytotoxic properties of this alkaloid.

The formation and fate of chlorinated organic substances in temperate and boreal forest soils

BACKGROUND, AIM AND SCOPE

Chlorine is an abundant element, commonly occurring in nature either as chloride ions or as chlorinated organic compounds (OCls). Chlorinated organic substances were long considered purely anthropogenic products; however, they are, in addition, a commonly occurring and important part of natural ecosystems. Formation of OCls may affect the degradation of soil organic matter (SOM) and thus the carbon cycle with implications for the ability of forest soils to sequester carbon, whilst the occurrence of potentially toxic OCls in groundwater aquifers is of concern with regard to water quality. It is thus important to understand the biogeochemical cycle of chlorine, both inorganic and organic, to get information about the relevant processes in the forest ecosystem and the effects on these from human activities, including forestry practices. A survey is given of processes in the soil of temperate and boreal forests, predominantly in Europe, including the participation of chlorine, and gaps in knowledge and the need for further work are discussed.

RESULTS

Chlorine is present as chloride ion and/or OCls in all compartments of temperate and boreal forest ecosystems. It contributes to the degradation of SOM, thus also affecting carbon sequestration in the forest soil. The most important source of chloride to coastal forest ecosystems is sea salt deposition, and volcanoes and coal burning can also be important sources. Locally, de-icing salt can be an important chloride input near major roads. In addition, anthropogenic sources of OCls are manifold. However, results also indicate the formation of chlorinated organics by microorganisms as an important source, together with natural abiotic formation. In fact, the soil pool of OCls seems to be a result of the balance between chlorination and degradation processes. Ecologically, organochlorines may function as antibiotics, signal substances and energy equivalents, in descending order of significance. Forest management practices can affect the chlorine cycle, although little is at present known about how.

DISCUSSION

The present data on the apparently considerable size of the pool of OCls indicate its importance for the functioning of the forest soil system and its stability, but factors controlling their formation, degradation and transport are not clearly understood. It would be useful to estimate the significance and rates of key processes to be able to judge the importance of OCls in SOM and litter degradation. Effects of forest management processes affecting SOM and chloride deposition are likely to affect OCls as well. Further standardisation and harmonisation of sampling and analytical procedures is necessary.

CONCLUSIONS AND PERSPECTIVES

More work is necessary in order to understand and, if necessary, develop strategies for mitigating the environmental impact of OCls in temperate and boreal forest soils. This includes both intensified research, especially to understand the key processes of formation and degradation of chlorinated compounds, and monitoring of the substances in question in forest ecosystems. It is also important to understand the effect of various forest management techniques on OCls, as management can be used to produce desired effects.

Enantiocontrolled synthesis of polychlorinated hydrocarbon motifs: a nucleophilic multiple chlorination process revisited

Polychlorinated hydrocarbon motifs have been synthesized in enantiomerically pure forms by means of nucleophilic multiple chlorinations of chiral epoxides, which stereospecifically incorporate halogen atoms into oxygenated molecular scaffolds. The present study demonstrates the scope of the N-chlorosuccinimide (NCS)/organophosphine reagent system that forms multiple sp(3)C-Cl bonds in a regularly repeating pattern with proper stereochemical configurations and evaluates its applicability to various epoxides having elaborate structures. It is noteworthy that tetrachlorinated motifs are produced in one step from bisepoxides by using NCS/Ph(3)P. Furthermore, Ph(2)PCl used in combination with NCS has been found to serve as a potentially useful alternative to NCS/Ph(3)P, especially for promoting dichlorination reactions of alkenyl-substituted epoxides.

Contrasting the seasonal variability of halogenated natural products and anthropogenic hexachlorocyclohexanes in the southern Norwegian atmosphere

Halogenated natural products (HNPs) are increasingly recognized as compounds of marine environmental samples. In this study, we explored whether the annual course of the concentrations of HNPs in ambient air samples was different from those of anthropogenic pollutants. For this purpose, air samples taken weekly at Lista, southern Norway, were analyzed by gas chromatography-mass spectrometry for anthropogenic aaeeee- (alpha-HCH) and aaaeee-hexachlorocyclohexane (gamma-HCH, lindane) isomers, as well as the HNPs 2,3,3',4,4',5,5'-heptachloro-1'-methyl-1,2'-bipyrrole (Q1), 2,4-di- and 2,4,6-tribromoanisole (24-DBA, 246-TBA), and 2,4,6-tribromophenol (246-TBP). Concentrations of HCH isomers were higher in the warmer summer months than in winter. By contrast, Q1, 24-DBA, 246-TBA, and 246-TBP showed much higher concentrations at the end of the year. Correlations between the concentrations of the compounds and air mass trajectories as well as further meteorological data are discussed. An unknown mixed halogenated substance was detected at high abundance during the summer months. High-resolution mass spectrometry and tandem mass spectrometric techniques were used to unravel the molecular structure, which was found to be C(7)H(8)Br(3)Cl, an elemental composition never reported before in the scientific literature.

Genomics of pyrrolnitrin biosynthetic loci: evidence for conservation and whole-operon mobility within gram-negative bacteria

Pyrrolnitrin (PRN) is a tryptophan-derived secondary metabolite produced by a narrow range of gram-negative bacteria. The PRN biosynthesis by rhizobacteria presumably has a key role in their life strategies and in the biocontrol of plant diseases. The biosynthetic operon that encodes the pathway that converts tryptophan to PRN is composed of four genes, prnA through D, whose diversity, genomic context and spread over bacterial genomes are poorly understood. Therefore, we launched an endeavour aimed at retrieving, by in vitro and in silico means, diverse bacteria carrying the prnABCD biosynthetic loci in their genomes. Analysis of polymorphisms of the prnD gene sequences revealed a high level of conservation between Burkholderia, Pseudomonas and Serratia spp. derived sequences. Whole-operon- and prnD-based phylogeny resulted in tree topologies that are incongruent with the taxonomic status of the evaluated strains as predicted by 16S rRNA gene phylogeny. The genomic composition of c. 20 kb DNA fragments containing the PRN operon varied in different strains. Highly conserved and distinct transposase-encoding genes surrounding the PRN biosynthetic operons of Burkholderia pseudomallei strains were found. A prnABCD-deprived genomic region in B. pseudomallei strain K96243 contained the same gene composition as, and shared high homology with, the flanking regions of the PRN operon in B. pseudomallei strains 668, 1106a and 1710b. Our results strongly suggest that the PRN biosynthetic operon is mobile. The extent, frequency and promiscuity of this mobility remain to be understood.

A colorimetric assay for steady-state analyses of iodo- and bromoperoxidase activities

The standard assay for iodoperoxidase activity is based on the spectrophotometric detection of triiodide formed during the enzymatic reaction. However, chemical instability of I3- has limited the method to high iodide concentrations and acidic conditions. Here we describe a simple spectrophotometric assay for the determination of iodoperoxidase activities of vanadium haloperoxidases based on the halogenation of thymol blue. The relation between color and chemical entities produced by the vHPO/H(2)O(2)/I(-) catalytic system was characterized. The method was extended to bromine and, for the first time, allowed measurement of both iodo- and bromoperoxidase activities using the same assay. The kinetic parameters (K(m) and k(cat)) of bromide and iodide for vanadium bromoperoxidase from Ascophyllum nodosum were determined at pH 8.0 from steady-state kinetic analyses. The results are concordant with an ordered two-substrate mechanism. It is proposed that halide selectivity is guided by the chemical reactivity of peroxovanadium intermediate rather than substrate binding. This method is superior to the standard I3- assay, and we believe that it will find applications for the characterization of other vanadium as well as heme haloperoxidases.

Proteomic identification, cDNA cloning and enzymatic activity of glutathione S-transferases from the generalist marine gastropod, Cyphoma gibbosum

Glutathione S-transferases (GST) were characterized from the digestive gland of Cyphoma gibbosum (Mollusca; Gastropoda), to investigate the possible role of these detoxification enzymes in conferring resistance to allelochemicals present in its gorgonian coral diet. We identified the collection of expressed cytosolic Cyphoma GST classes using a proteomic approach involving affinity chromatography, HPLC and nano-spray liquid chromatography-tandem mass spectrometry (LC-MS/MS). Two major GST subunits were identified as putative mu-class GSTs; while one minor GST subunit was identified as a putative theta-class GST, apparently the first theta-class GST identified from a mollusc. Two Cyphoma GST cDNAs (CgGSTM1 and CgGSTM2) were isolated by RT-PCR using primers derived from peptide sequences. Phylogenetic analyses established both cDNAs as mu-class GSTs and revealed a mollusc-specific subclass of the GST-mu clade. These results provide new insights into metazoan GST diversity and the biochemical mechanisms used by marine organisms to cope with their chemically defended prey.

Critical view on the monochlorodimedone assay utilized to detect haloperoxidase activity

The current study aimed to identify the halogenating enzymes involved in the biosynthesis of the ambigols A, B, C and tjipanazole D, isolated from the cyanobacterium Fischerella ambigua. Haloperoxidase (HPO) activity within F. ambigua was therefore assayed spectrophotometrically by using monochlorodimedone (MCD) during protein purification. This strategy revealed the isolation of a protein positive in the MCD-assay, but an involvement in halogenating processes could not be verified. N-terminal sequencing rather demonstrated homology to cytochrome c(6) from other cyanobacteria and green algae. From our findings it thus has to be concluded that the spectrophotometrical MCD-assay routinely used to detect HPO activity may yield false positive results, mainly since the assay focuses on the decline of the educt and not on the formation of the product. Our data indicate that the reaction of MCD with proteins of the cytochrome c- family leads to unspecific products.

Formation of organobrominated compounds in the presence of bromide under simulated atmospheric aerosol conditions

Photobromination of phenol takes place upon UV/Vis irradiation of FeIII and bromide under acidic conditions, and most likely involves the brominating agent Br2(-*). Bromination is also observed in the presence of nitrate and bromide under UV irradiation, most likely involving Br2(-*) formed upon oxidation of bromide by *OH. Moreover, quantitative bromination of phenol is observed in the dark in the presence of hydrogen peroxide and bromide. This process is strongly favored under acidic conditions, but a residual, pH-independent bromination pathway is also present. The rates and yields of bromination (up to 100%) are considerably higher than those reported for chlorination under comparable conditions, suggesting that the higher activity of bromine species could compensate for the lower concentration of bromide ions in aerosol compared to chlorides. The reported processes are potent tial sources of reactive bromine species (Br2(-*), HBrO) and aromatic bromo derivatives in atmospheric aerosols, in particular after the acidification process linked with aerosol aging.

Antimalarial benzoquinones from an endophytic fungus, Xylaria sp

Two novel benzoquinone metabolites, 2-chloro-5-methoxy-3-methylcyclohexa-2,5-diene-1,4-dione ( 1) and xylariaquinone A ( 2) together with two known compounds were isolated from an endophytic fungus, Xylaria sp. Their structures were assigned by analysis of spectroscopic data, and the structures of 1 and 3 were also confirmed by single-crystal X-ray data. Compounds 1 and 2 showed in vitro activity against Plasmodium falciparum, K1 strain, with IC 50 values of 1.84 and 6.68 microM and cytotoxicity against African green monkey kidney fibroblasts (Vero cells) with IC 50 values of 1.35 and >184 microM, respectively.

The Application of19F Nuclear Magnetic Resonance to Investigate Microbial Biotransformations of Organofluorine Compounds

Fluorinated organic compounds, although rare in nature, are significant environmental contaminants owing to the numerous applications for which this class of compounds is employed. It is important that biodegradation of these compounds can be readily assessed in order to provide information on their fate in the environment. Fluorine-19 nuclear magnetic resonance (19F NMR) spectroscopy has emerged as a very useful technique to readily determine the catabolism of fluorinated aromatic compounds by microorganisms, either in whole cell or cell-free systems. The principal advantage of this technique is that fluorinated compounds can be observed directly in the culture supernatant or enzyme assay, without purification or derivatization. In this review an account of the application of 19F NMR in the study of microbial metabolism of organofluorine compounds is presented.

Widespread capacity to metabolize polychlorinated biphenyls by diverse microbial communities in soils with no significant exposure to PCB contamination

The purpose of this work was to determine the extent of microbial metabolic potential for polychlorinated biphenyls (PCBs) in soils that have had no previous exposure to this class of xenobiotic pollutants. Soil and sediment samples of distinct characteristics from six sites in Germany were used to inoculate PCB oil (Aroclor 1242) microdroplets. All samples yielded multispecies biofilms, as revealed by single-strand conformation polymorphism (SSCP) analyses of polymerase chain reaction (PCR) analysis of 16S rRNA genes, and sequence analysis of the main amplicons. Microbes representing 20 different operational taxonomic units (OTUs) were identified in the biofilms, but only a few were common to all biofilms, namely those closely related to Aquabacterium sp., Caulobacter sp., Imtechium assamiensis, Nevskia ramosa, Parvibaculum lavamentivorans and Burkholderia sp. The PCB biofilm communities were always distinct from control biofilms developing from the same samples in the absence of PCB. All PCB droplet-grown biofilms degraded multiple PCB congeners but differed in the congener spectra they degraded. These findings reveal that microbial potential to degrade PCBs is widespread in soils that have not been subjected to PCB contamination, and that this potential is characteristic of consortia of very diverse phylogenetic composition.

Chlorinated lipids and fatty acids: an emerging role in pathology

Although the existence of halogenated lipids in lower organisms has been known for many years, it is only since the 1990s that interest in their occurrence in mammalian systems has developed. Chlorinated (and other halogenated) lipids can arise from oxidation by hypohalous acids, such as HOCl, which are products of the phagocytic enzyme myeloperoxidase and are generated during inflammation. The major species of chlorinated lipids investigated to date are chlorinated sterols, fatty acid and phospholipid chlorohydrins, and alpha-chloro fatty aldehydes. While all of these chlorinated lipids have been shown to be produced in model systems from lipoproteins to cells subjected to oxidative stress, as yet only alpha-chloro fatty aldehydes, such as 2-chlorohexadecanal, have been detected in clinical samples or animal models of disease. alpha-Chloro fatty aldehydes and chlorohydrins have been found to have a number of potentially pro-inflammatory effects ranging from toxicity to inhibition of nitric oxide synthesis and upregulation of vascular adhesion molecules. Thus evidence is building for a role of chlorinated lipids in inflammatory disease, although much more research is required to establish the contributions of specific compounds in different disease pathologies. Preventing chlorinated lipid formation and indeed other HOCl-induced damage, via the inhibition of myeloperoxidase, is an area of growing interest and may lead in the future to antimyeloperoxidase-based antiinflammatory therapy. However, other chlorinated lipids, such as punaglandins, have beneficial effects that could offer novel therapies for cancer.

Natural production of organic bromine compounds in Berlin Lakes

Berlin surface waters are characterized by elevated concentrations of organic bound bromine (up to 35 microg/L) in late summer. Organic bromine compounds in lakes are of significant importance because human life is closely connected to fresh water. Apart from recreational use, fresh water is frequently used for the production of drinking water, e.g., after bank filtration. Therefore the source, particularly the mechanism responsible for the formation is studied. Field studies indicate that the organic bromine compounds, measured as adsorbable organic bromine (AOBr), are autochthonous. Staggered maxima concentrations of chlorophyll-a, DOC and AOBr indicate that phototrophic organisms might contribute to the AOBr after death. The involvement of phototrophic organisms was established in the laboratory using surface water and/or cultures of organisms. Light and the presence of phototrophic organisms are essential for an AOBr production. Phototrophic organisms incorporate bromide, which is released randomly and after cell death. A part of the incorporated bromide is used for the formation of organic bromine compounds in the cell. After death of the organisms the brominated compounds and the incorporated bromide are released into the water phase, and an extracellular AOBr production can lead to a further formation of AOBr, most probably due to the parallel release of haloperoxidases.

Polybrominated hexahydroxanthene derivatives (PBHDs) and other halogenated natural products from the Mediterranean sponge Scalarispongia scalaris in marine biota

Structures of polybrominated hexahydroxanthene derivatives (PBHDs) previously detected in commercial fish from the Mediterranean Sea and mussels from New Zealand were assigned to 2,7-dibromo-4a-bromomethyl-1,1-dimethyl-2,3,4,4a,9,9a-hexahydro-1H-xanthene (TriBHD) and 2,5,7-tribromo-4a-bromomethyl-1,1-dimethyl-2,3,4,4a,9,9a-hexahydro-1H-xanthene (TetraBHD) by comparing their gas chromatography/mass spectrometry (GC/MS) features with isolates from an Australian sponge of the Cacospongia genus. Because of the geographic distance between the Mediterranean Sea in Europe (origin of the fish) and Australia (origin of the sponge), a closely related sponge, Scalarispongia scalaris, was collected in the Mediterranean Sea and analyzed for PBHDs and other halogenated compounds. The Mediterranean sponge contained the PBHDs at 37 mg/kg dry weight. Using quantitative standards for the first time, the PBHD concentrations in fish and mussel samples published earlier were re-examined. Concentrations of up to 1 mg/kg TriBHD and 0.5 mg/kg TetraBHD were determined in the lipids. No correlation with 2,2', 4,4', 5,5'-hexachlorobiphenyl (PCB 153) or p,p'-DDE was found, which is in agreement with other marine halogenated natural products detected in the fish samples. Besides the PBHDs, further unknown halogenated compounds were detected in the Mediterranean sponge, some of which were also detected in commercial fish. GC/electron ionization-MS analysis showed that a major mixed-halogenated compound in the sponge had a molecular ion at m/z 480 and contained three bromines, three chlorines, and 9-10 carbons. No corresponding structure has been described for this feature in the scientific literature. This sponge secondary metabolite and potential novel halogenated natural product was also detected in commercial fish. Another prominent mixed halogenated compound detected both in sponge and fish was the dibromotrichloro monoterpene MHC-1 (C(10)H(13)Br(2)Cl(3)).

Quantitative determination of absolute organohalogen concentrations in environmental samples by X-ray absorption spectroscopy

An in situ procedure for quantifying total organic and inorganic Cl concentrations in environmental samples based on X-ray absorption near-edge structure (XANES) spectroscopy has been developed. Cl 1s XANES spectra reflect contributions from all Cl species present in a sample, providing a definitive measure of total Cl concentration in chemically heterogeneous samples. Spectral features near the Cl K-absorption edge provide detailed information about the bonding state of Cl, whereas the absolute fluorescence intensity of the spectra is directly proportional to total Cl concentration, allowing for simultaneous determination of Cl speciation and concentration in plant, soil, and natural water samples. Absolute Cl concentrations are obtained from Cl 1s XANES spectra using a series of Cl standards in a matrix of uniform bulk density. With the high sensitivity of synchrotron-based X-ray absorption spectroscopy, Cl concentration can be reliably measured down to the 5-10 ppm range in solid and liquid samples. Referencing the characteristic near-edge features of Cl in various model compounds, we can distinguish between inorganic chloride (Cl(inorg)) and organochlorine (Cl(org)), as well as between aliphatic Cl(org) and aromatic Cl(org), with uncertainties in the range of approximately 6%. In addition, total organic and inorganic Br concentrations in sediment samples are quantified using a combination of Br 1s XANES and X-ray fluorescence (XRF) spectroscopy. Br concentration is detected down to approximately 1 ppm by XRF, and Br 1s XANES spectra allow quantification of the Br(inorg) and Br(org) fractions. These procedures provide nondestructive, element-specific techniques for quantification of Cl and Br concentrations that preclude extensive sample preparation.

Monobromo and higher brominated congeners of the marine halogenated natural product 2,3,3',4,4',5,5'-heptachloro-1'-methyl-1,2'-bipyrrole (Q1)

The marine halogenated natural product 2,3,3',4,4',5,5'-heptachloro-1'-methyl-1,2'-bipyrrole (Q1) is widely distributed in the environment. In this study, we screened samples which have previously been found to contain remarkably high residues of Q1 (blubber of marine mammals from Australia, samples from Antarctica, human milk from the Faroe Island) for the additional presence of mixed chlorinated and brominated congeners. Using GC/ECNI-MS, all samples tested were positive and many contained four out of five possible bromohexachloro congeners (BrCl6-MBPs), five out of 14 possible dibromopentachloro congeners (Br2Cl5-MBPs), five of 21 possible tribromotetrachloro-congeners (Br3Cl4-MBPs), as well as several higher brominated congeners. About 20 heptahalo congeners of Q1 are described for the first time in the scientific literature. Isomers eluted within about one minute, respectively. Hence it is possible, that the peak clusters identified may be composed of more, co-eluting congeners. Similarities in the GC/ECNI-MS mass spectra with polychlorinated biphenyls (PCBs) were addressed. We also suggest an acronym system similar to that in use for polychlorinated biphenyls that may simplify the use of this substance class in scientific papers. In the samples from Australia, BrCl6-MBPs and Br2Cl5-MBPs amounted for 7-27.5% and 0.4-4.2% of Q1, respectively whereas Br3Cl4-MBPs and higher brominated MBPs were found in the range of <1% of Q1 or less.

Chloro- and bromophenols from cultures of Mycena alcalina

Three new chlorinated phenols have been isolated from mycelial cultures of the mushroom Mycena alcalina. Their structures were determined by mass spectrometry and 1D and 2D NMR experiments. Addition of bromide to the medium resulted in the production of the corresponding brominated phenols. In addition, small amounts of the nonhalogenated precursor were also isolated, indicating that the halogenated metabolites are generated by a regioselectively operating halogenase.

Exploring gradients of halogens and zinc in the surface and subsurface of Nereis jaws

The outstanding mechanical properties of impact-bearing tissues, such as Nereis jaws, make their morphology and chemical composition a subject of particular interest. The complex structure of the jaw was recently reported to exhibit molecular gradients that were closely correlated with stiffness and hardness.(18) Accordingly, we have explored the spatial distribution and bonding chemistries of Zn and the halogens in the surface structure of the jaws. Using secondary ion mass spectrometry (SIMS) and scanning electron microscopy (SEM), we found that Cl, Br, and I distributions are enhanced in surface layers of the basal protected portion of the jaw but are shifted to greater depths toward the exposed jaw tip. There are thus two complementary halogen gradients in the jaw: one on the surface that decreases from the base to the tip, coupled to an increasing one in the subsurface layers. The outer surface coating appeared to have granular morphology, in contrast to the anisotropic, fibrous core that dominates the subarchitecture. Using X-ray photoelectron spectroscopy (XPS), we discovered that Zn, I, and Br in the jaws have single chemical environments whereas chlorine is present in two distinct modes (Cl-Zn and Cl-C). Given the inverse relationship between surface exposure and halogen abundance in the jaws, it is unlikely that the halogens contribute directly to mechanical properties such as wear and hardness.

Transcriptional Activation of Dehalorespiration

Desulfitobacterium dehalogenans can use chlorinated aromatics including polychlorinated biphenyls as electron acceptors in a process called dehalorespiration. Expression of the cpr gene cluster involved in this process is regulated by CprK, which is a member of the CRP/FNR (cAMP-binding protein/fumarate nitrate reduction regulatory protein) family of helix-turn-helix transcriptional regulators. High affinity interaction of the chlorinated aromatic compound with the effector domain of CprK triggers binding of CprK to an upstream target DNA sequence, which leads to transcriptional activation of the cpr gene cluster. When incubated with oxygen or diamide, CprK undergoes inactivation; subsequent treatment with dithiothreitol restores activity. Using mass spectrometry, this study identifies two classes of redox-active thiol groups that form disulfide bonds upon oxidation. Under oxidative conditions, Cys105, which is conserved in FNR and most other CprK homologs, forms an intramolecular disulfide bond with Cys111, whereas an intermolecular disulfide bond is formed between Cys11 and Cys200. SDS-PAGE and site-directed mutagenesis experiments indicate that the Cys11/Cys200 disulfide bond links two CprK subunits in an inactive dimer. Isothermal calorimetry and intrinsic fluorescence quenching studies show that oxidation does not change the affinity of CprK for the effector. Therefore, reversible redox inactivation is manifested at the level of DNA binding. Our studies reveal a strategy for limiting expression of a redox-sensitive pathway by using a thiol-based redox switch in the transcription factor.

Cross-kingdom hormonal signaling: an insight from thyroid hormone functions in marine larvae

Thyroid hormones (THs) are small, lipophilic signaling molecules built from tyrosine and iodine. TH action is well characterized in vertebrates, where these molecules play a fundamental role as regulators of development, metabolism, growth and differentiation. Increasing evidence suggests that THs also function in a variety of invertebrate species. Two alternative sources of hormone for animals are exogenous (from food items) and endogenous synthesis. We propose that exogenous THs can convey environmental information as well as regulate metabolism, revealing new communication avenues between organisms from different kingdoms. While such modes of cross-kingdom communication have been previously considered for fatty acid-based signaling and steroid hormones in plant-animal interactions, this is the first attempt to explore such a mode of action for TH signaling. We suggest that exogenous sources of TH (from food) may have been ancestral, while the ability to synthesize TH endogenously may have evolved independently in a variety of metazoans, resulting in a diversity of signaling pathways and, possibly, morphological structures involved in TH-signaling.

CprK crystal structures reveal mechanism for transcriptional control of halorespiration

Halorespiration is a bacterial respiratory process in which haloorganic compounds act as terminal electron acceptors. This process is controlled at transcriptional level by CprK, a member of the ubiquitous CRP-FNR family. Here we present the crystal structures of oxidized CprK in presence of the ligand ortho-chlorophenolacetic acid and of reduced CprK in absence of this ligand. These structures reveal that highly specific binding of chlorinated, rather than the corresponding non-chlorinated, phenolic compounds in the NH(2)-terminal beta-barrels causes reorientation of these domains with respect to the central alpha-helix at the dimer interface. Unexpectedly, the COOH-terminal DNA-binding domains dimerize in the non-DNA binding state. We postulate the ligand-induced conformational change allows formation of interdomain contacts that disrupt the DNA domain dimer interface and leads to repositioning of the helix-turn-helix motifs. These structures provide a structural framework for further studies on transcriptional control by CRP-FNR homologs in general and of halorespiration regulation by CprK in particular.

Inferring the chemical mechanism from structures of enzymes

Chemistry has once again embraced the study of enzyme mechanism as a core discipline. Chemists are uniquely able to contribute to the analysis of enzymes through their understanding of the reactivity of atoms. In this tutorial review for the Corday-Morgan medal, I will concentrate on the work from my lab over the past six years. I discuss enzymes which transform carbohydrates and incorporate halogens. The tutorial review will emphasise the strengths and limitations of structural biology as a means to deducing the chemical mechanism.

Furoquinoline alkaloids fromMelicope bonwickii(F.Muell.) T.Hartley

Investigation on the leaves of Melicope bonwickii (F.Muell.) T.Hartley (Rutaceae) afforded a new 7-(2'-hydroxy-3'-chloroprenyloxy)-4-methoxyfuroquinoline (1) together with the known 7-(2',3'-epoxyprenyloxy)-4-methoxyfuroquinoline (2), evellerine (3) kokusaginine (4) and an amide aurantiamide acetate (5). Compounds 1 and 2 showed significant activity against cervical cell lines (Hela).

Experimental and theoretical studies on formation and degradation of chloro organic compounds

Studies on oxidation of tert-butyl ethers in the presence of chloride ions proved that acid medium favoured formation of chloro organic compounds. 1,2-Dichloro-2-methylpropane, 3-chloro-2-chloromethylpropene were identified among the reaction products. Presence of these compounds was identified both in the case when methyl-tert-butyl ether (MTBE) and ethyl-tert-butyl ether (ETBE) were subjected to reaction. Reaction products were analysed by gas chromatography method with application of -FID, -MS and -AED detectors. On the basis of experimental data, the path of tert-butyl ethers conversion to dichloro products was proposed. It was found that the identified chloro derivatives could be formed both by ionic and radical reactions. In order to confirm this thesis for the proposed scheme of reaction, the theoretical calculations of molecular simulation of the reaction paths were performed.

De novo formation of chloroethyne in soil

To date, chloroethyne in the environment has been proposed to occur as a reactive intermediate during the reductive dechlorination of tri- and tetrachloroethene with zerovalent metals. Such artificial conditions might possibly be found at organohalide-contaminated sites that are surrounded by remediation barriers made of metallic iron. In this paper, it is shown that the highly reactive chloroethyne is also a product of natural processes in soil. Soil air samples from three differentterrestrial ecosystems of Northern Germany showed significant chloroethyne concentrations, besides other naturally produced monochlorinated compounds, such as chloromethane, chloroethane and chloroethene. Measured amounts range from 5 to 540 pg chloroethyne in air purged from 1 L of soil. A possible route of chloroethyne formation in soil is discussed, where chloroethyne is probably produced as a byproduct of the oxidative halogenation of aromatic compounds in soil. A series of laboratory studies, using the redox-sensitive catechol as a discrete organic model compound, showed the formation of chloroethyne when Fe3+ and hydrogen peroxide were added to the system. We therefore propose that the natural formation of chloroethyne in soil proceeds via oxidative cleavage of a quinonic system in the presence of the ubiquitous soil component chloride.

Dechlorodauricumine from cultured roots of Menispermum dauricum

Dechlorodauricumine, a possible organic substrate for biochlorination, was isolated from cultured roots of Menispermum dauricum, a rich source of chlorinated alkaloids. Its structure was established by spectroscopic and chemical methods.

Tetra- and tribromophenoxyanisoles in marine samples from Oceania

Some methoxylated polybrominated diphenyl ethers (MeO-BDEs) are known halogenated natural products (HNPs) and are frequently detected in higher organisms of the marine environment. In this study we demonstrate that a prominent MeO-BDE, previously detected in marine mammals from Australia, is identical to 3,5-dibromo-2-(2',4'dibromo)phenoxyanisole (BC-3, 6-MeO-BDE 47). Up to 1.9 mg/ kg of 6-MeO-BDE 47 was present in cetaceans from Australia, 0.2-0.3 mg/kg in two crocodile eggs from Australia, but concentrations of 1 or 2 orders of magnitude lower were found in shark liver oil from NewZealand and in marine mammals from Africa and the Antarctic. Concentrations of 6-MeO-BDE 47 in samples from Australia were in the same range as anthropogenic pollutants such as PCB 153 and p,p'-DDE. Along with 6-MeO-BDE 47 and the known HNP 4,6-dibromo-2-(2',4'-dibromo)phenoxyanisole (BC-2, 2'-MeO-BDE 68), several tribromophenoxyanisoles (MeO-triBDE) were present in tissue of Australian cetaceans. To determine their structure, abiotic debromination experiments were performed using 6-MeO-BDE 47 and 2'-MeO-BDE 68 and superreduced dicyanocobalamine. These experiments resulted in formation of eight MeO-triBDEs, all of which were detected in the cetacean samples. Five of these eight MeO-triBDEs could be identified based on two standard compounds as well as gas chromatographic and mass spectrometric features. It was also shown that the first eluting isomer (compound 1), 6-MeO-BDE 17 (compound 2), and 2-MeO-BDE 39 (compound 5) were the most prominent MeO-triBDEs in the Australian cetacean samples. The concentrations of the MeO-triBDEs in two cetacean samples were 0.20 and 0.36 mg/kg, respectively. Although the reductive debromination with dicyanocobalamine resulted in a different congener pattern than was found in the marine mammals, it could not be excluded that the tribromo

Brominated flame retardants and other organobromines in Norwegian predatory bird eggs

A set of 62 unhatched eggs was collected from six different predatory bird species throughout Norway after incubation period was completed. They were analysed for PBDE, PBB, TBBP A and naturally occurring halogenated compounds. BDE 47, 99 and 153 were the dominating congeners, with species dependent PBDE patterns. BDE 153 was observed as the most abundant congener in eggs of peregrine falcon, golden eagle and merlin. The highest PBDE level (sum of nine congeners) was found in eggs of white-tailed sea eagle with up to 800ng/gww (median sumPBDE: 184ng/gww), followed by eggs of peregrine falcon and osprey (median sumPBDE: 155 and 105ng/gww, respectively). Golden eagle eggs showed the lowest concentration of all species (median sumPBDE: 3ng/gww). The levels in the peregrine falcon are similar to those found earlier in the Baltic region [Lindberg, P., Sellstrom, U., Haggberg, L., de Wit, C.A., 2004. Higher brominated diphenyl ethers and hexabromocyclododecane found in eggs of peregrine falcons (Falco peregrinus) breeding in Sweden. Environmental Science & Technology. 38 (1), 93-96]. The differences between species are not fully explainable, due to lack of data from the major food species. BB 101 and 153 were found in eggs of all investigated bird species. Especially in samples of white-tailed sea eagle, peregrine falcon and goshawk additional unknown penta- and hexabrominated biphenyls were detected. TBBP A was detected in all of eight eggs analysed sampled from four different bird of prey species. The naturally occurring halogenated compounds Q1, the dibromotrichloro monoterpene MHC-1, and 2,4,6-tribromoanisole (TBA) were detected in all of seven analysed samples except for one peregrine falcon egg.

Tryptophan 7-halogenase (PrnA) structure suggests a mechanism for regioselective chlorination

Chlorinated natural products include vancomycin and cryptophycin A. Their biosynthesis involves regioselective chlorination by flavin-dependent halogenases. We report the structural characterization of tryptophan 7-halogenase (PrnA), which regioselectively chlorinates tryptophan. Tryptophan and flavin adenine dinucleotide (FAD) are separated by a 10 angstrom-long tunnel and bound by distinct enzyme modules. The FAD module is conserved in halogenases and is related to flavin-dependent monooxygenases. On the basis of biochemical studies, crystal structures, and by analogy with monooxygenases, we predict that FADH2 reacts with O2 to make peroxyflavin, which is decomposed by Cl-. The resulting HOCl is guided through the tunnel to tryptophan, where it is activated to participate in electrophilic aromatic substitution.

Halogenated natural products in five species of Antarctic sponges: compounds with POP-like properties?

Purified extracts of five species of Antarctic sponges (Demospongiae: Kirkpatrickia variolosa, Artemisina apollinis, Phorbas glaberrima, and Halichondria sp. and Calcarea: Leucetta antarctica) from King George Island were analyzed by GC/MS for the presence of persistent and lipophilic halogenated compounds to identify bioaccumulative halogenated natural products. Sample extracts were prepared using methods identical for the determination of POPs, namely, microwave-assisted extraction with organic solvents, gel permeation chromatography, and column chromatography on deactivated silica. In addition, samples were treated with sulfuric acid to remove acid-destructible compounds. PCBs were not detectable and only traces of lindane, p,p'-DDE, and alpha-HCH were detected in these samples in decreasing order of abundance, underscoring their uncontaminated state. In contrast, 146 brominated compounds were identified by correct isotopic ratios m/z 79 and 81, 50% of which eluted prior to lindane including the most abundant peaks. Each sponge sample contained > or = 35 brominated compounds of natural origin, 14 of which were detected in all species. Estimated concentrations ranged from the high ng/kg to mg/kg (air-dried weights) and relative distributions of the same compounds in different sponges were highly variable. The high abundance of these compounds relative to known anthropogenic pollutants strongly suggests a natural origin. Multiple mode (EI-, ECNI-, and PCI-) GC/MS enabled identification of an aliphatic ketone tentatively identified as 1,1,2-tribromo-oct-1-en-3-one, present in all species but highest in Phorbas glaberrima. Several halogenated phenols including 2,4,6-tribromophenol were also abundant in Phorbas glaberrima as were halogenated anisoles in lower relative abundances. The halogenated phenols were analyzed without derivatization. The sample of Halichondria sp. contained the dibromotrichloro monoterpene MHC-1, a recently described environmental contaminant in fish and seals. Retrospective analysis of other marine samples confirmed that 2,4,6-tribromophenol was present in seal blubber from both the Arctic and the Antarctic. The presence of naturally occurring organohalogens such as 2,4,6-tribromophenol and MHC-1 in Antarctic marine invertebrates thus provides a link to their occurrence in marine mammals.

Enantiomer fractions of organic chlorinated pesticides in arctic marine ice fauna, zooplankton, and benthos

Stereoisomers of chiral chlorinated pesticides (alpha-HCH (HCH = hexachlorocyclohexane), trans- and cis-chlordane, MC5, o,p'-DDT) were quantified in arctic marine invertebrates (ice-associated amphipods Gammarus wilkitzkii, pelagic copepods Calanus hyperboreus, krill Thysanoessa inermis, and amphipods Themisto libellula, and benthic amphipods Paramphithoe hystrix). Enantiomer fractions (EFs) were calculated to investigate the influence of habitat, geographic area, and diet on selective bioaccumulation of the (-)- or (+)-enantiomer. Depletion of the (+)-alpha-HCH enantionmer increased from ice fauna to zooplankton to benthos, corresponding to previous reports of EF variations with depth. Chlordanes and o,p'-DDT also showed the strongest enantioselective bioaccumulation in benthic amphipods and less so in zooplankton and ice fauna, which had closer to racemic EFs. Neither diet nor geographic area explained EF differences among samples. Nonracemic EFs in benthos may be related to stereoselective biotransformation, but is most likely reflecting vertical distribution of EFs in the water column and sediments, as demonstrated earlier for alpha-HCH in the Canadian and European Arctic.

Isolation and structure elucidation of the new fungal metabolite (-)-xylariamide A

Chemical investigations of the terrestrial microfungus Xylaria sp. have afforded the new natural product (-)-xylariamide A (1). The gross structure of 1 was determined by interpretation of 1D and 2D NMR, UV, IR, and MS data. Confirmation of the structure and the absolute stereochemistry of 1 were determined by the total synthesis of (+)-xylariamide A (2). Synthetic 2 was produced by N,O-bis(trimethylsilyl)acetamide-induced coupling of 3-chloro-L-tyrosine (3) with (E)-but-2-enedioic acid 2,5-dioxo-pyrrolidin-1-yl ester methyl ester (4). Optical rotation comparison of 1 with 2 indicated that the natural product (1) contained 3-chloro-D-tyrosine. Both enantiomers of xylariamide A were tested in a brine shrimp lethality assay, and only the natural product (1) showed toxicity.