One-dimensional Zn(II) oligo(phenyleneethynylene)dicarboxylate coordination polymers: Synthesis, crystal structures, thermal and photoluminescent properties

The rigid, π-conjugated dicarboxylic acid 1,4-bis-[2-(4-carboxyphenyl)ethynyl]-2,5-dihexylbenzene {HO₂C[PEP(hexyl)₂EP]CO₂H} has been used to synthesise the new crystalline coordination polymers {Zn(O₂C[PEP(hexyl)₂EP]CO₂)(DMF)₂} (1) and {Zn(O₂C[PEP(hexyl)₂EP]CO₂)(DEF)₂} (2) in N,N-dimethylformamide (DMF) and N,N-diethylformamide (DEF), respectively, under mild conditions. Single-crystal X-ray crystallography revealed that 1 and 2 are isostructural and consist of uncharged zigzag coordination chains in which [Zn(formamide)₂]²⁺ fragments are bridged by (O₂C[PEP(hexyl)₂EP]CO₂)²⁻ ligands. The zigzag chains possess different intra-chain Zn?Zn?Zn angles due to the different volumes of the coordinating formamide molecules and subtle differences in the hydrophobic inter-chain interactions. Upon heating 1 and 2 to 200 °C, removal of the coordinating formamide molecules occurs, yielding the formamide-free compounds 1-DMF and 2-DEF of composition {Zn(O₂C[PEP(hexyl)₂EP]CO₂)}. According to powder X-ray diffraction and FT-IR spectroscopy studies, these materials are not crystalline but still possess partial ordering of intact, yet modified coordination chains in a structural arrangement which appears to be related to the respective parent compounds. Compounds 1, 2, 1-DMF and 2-DEF exhibit blue photoluminescence. The emission maxima of 1-DMF and 2-DEF are red-shifted by ca. 25 nm with respect to λ_max of 1 and 2, respectively.     

Function and quality of kidneys after cold storage, machine perfusion, or retrograde oxygen persufflation: Results from a porcine autotransplantation model

Objectives

Especially for preservation of marginal donor organs, machine perfusion (MP) and retrograde oxygen persufflation (ROP) are alternatives to cold storage (CS). Using a porcine kidney autotransplantation model we compared metabolic and morphologic effects of CS, ROP, and MP on kidneys exposed to warm ischemia.

Methods

Kidneys of 21 pigs were exposed in situ to warm ischemia for 60 min. The kidneys were randomly allocated to three experimental groups, each receiving a 4-h treatment of either cold storage, machine perfusion, or retrograde oxygen persufflation. Tissue samples were examined for malondialdehyde and histological changes. Daily blood samples were examined for creatinine levels.

Results

Seven days after transplantation, the plasma creatinine levels in the CS and MP groups were still significantly elevated above the baseline values. In the ROP group, all animals exhibited nearly normal creatinine levels. Malondialdehyde, an indicator of lipidperoxidation, was dramatically increased in the machine perfused kidneys on day 7, whereas the malondialdehyde levels in the other two groups were near normal values. The MP kidneys exhibited the most striking histological changes.

Conclusion

Though MP has been well introduced in organ transplantation, in our opinion, it must still be optimized and standardized. It is necessary to clarify questions such as whether there is a need for oxygenation during perfusion, the length of perfusion, the impact of pressure, and the effects of additional scavengers. The results of the present study suggest the reconsideration of the ROP-technique for the preservation of predamaged donor grafts especially of NHBD and further studies, comparing MP and ROP upon long term preservation are strongly encouraged.     

Cytochrome c-d regulates developmental apoptosis in the Drosophila retina

The role of cytochrome c (Cyt c) in caspase activation has largely been established from mammalian cell-culture studies, but much remains to be learned about its physiological relevance in situ. The role of Cyt c in invertebrates has been subject to considerable controversy. The Drosophila genome contains distinct cyt c genes: cyt c-p and cyt c-d. Loss of cyt c-p function causes embryonic lethality owing to a requirement of the gene for mitochondrial respiration. By contrast, cyt c-d mutants are viable but male sterile. Here, we show that cyt c-d regulates developmental apoptosis in the pupal eye. cyt c-d mutant retinas show a profound delay in the apoptosis of superfluous interommatidial cells and perimeter ommatidial cells. Furthermore, there is no apoptosis in mutant retinal tissues for the Drosophila homologues of apoptotic protease-activating factor 1 (Ark) and caspase 9 (Dronc). In addition, we found that cyt c-d--as with ark and dronc-regulates scutellar bristle number, which is known to depend on caspase activity. Collectively, our results indicate a role of Cyt c in caspase regulation of Drosophila somatic cells.     

Expression of BjMT2, a metallothionein 2 from Brassica juncea, increases copper and cadmium tolerance in Escherichia coli and Arabidopsis thaliana, but inhibits root elongation in Arabidopsis thaliana seedlings

The protective function of a plant type-2 metallothionein was analysed after expression in Escherichia coli and in Arabidopsis thaliana seedlings. BjMT2 from Brassica juncea was expressed in E. coli as a TrxABjMT2 fusion protein. After affinity chromatography and cleavage from the TrxA domain, pure BjMT2 protein was obtained which strongly reacted with the thiol reagent monobromobimane. Escherichia coli cells expressing the TrxABjMT2 fusion were more tolerant to Cu2+ and Cd2+ exposure than control strains. Likewise, when BjMT2 cDNA was expressed in A. thaliana under the regulation of the 35S promoter, seedlings exhibited an increased tolerance against Cu2+ and Cd2+ based on shoot growth and chlorophyll content. Analysis of transiently transformed cells of A. thaliana and tobacco leaves by confocal laser scanning microscopy (CLSM) revealed exclusive cytosolic localization of a BjMT2::EGFP (enhanced green fluorescent protein) fusion protein in control and heavy metal-exposed plant cells. Remarkably, ectopic expression of BjMT2 reduced root growth in the absence of heavy metal exposure, whereas in the presence of 50 or 100 microM Cu2+ root growth in control and transgenic lines was identical. The results indicate that in A. thaliana, root and shoot development are differentially affected by ectopic expression of BjMT2.     

Characterization and phylogenomic analysis of Breznakiella homolactica gen. nov. sp. nov. indicate that termite gut treponemes evolved from non-acetogenic spirochetes in cockroaches

Spirochetes of the genus Treponema are surprisingly abundant in termite guts, where they play an important role in reductive acetogenesis. Although they occur in all termites investigated, their evolutionary origin is obscure. Here, we isolated the first representative of ‘termite gut treponemes’ from cockroaches, the closest relatives of termites. Phylogenomic analysis revealed that Breznakiella homolactica gen. nov. sp. nov. represents the most basal lineage of the highly diverse ‘termite cluster I', a deep-branching sister group of Treponemataceae (fam. ‘Termitinemataceae’) that was present already in the cockroach ancestor of termites and subsequently coevolved with its host. Breznakiella homolactica is obligately anaerobic and catalyses the homolactic fermentation of both hexoses and pentoses. Resting cells produced acetate in the presence of oxygen. Genome analysis revealed the presence of pyruvate oxidase and catalase, and a cryptic potential for the formation of acetate, ethanol, formate, CO₂ and H₂ - the fermentation products of termite gut isolates. Genes encoding key enzymes of reductive acetogenesis, however, are absent, confirming the hypothesis that the ancestral metabolism of the cluster was fermentative, and that the capacity for acetogenesis from H₂ plus CO₂ - the most intriguing property among termite gut treponemes - was acquired by lateral gene transfer.     

Biochemical evidence that berberine bridge enzyme belongs to a novel family of flavoproteins containing a bi-covalently attached FAD cofactor

Berberine bridge enzyme (BBE) is involved in the transformation of (S)-reticuline to (S)-scoulerine in benzophenanthridine alkaloid biosynthesis of plants. In this report, we describe the high level expression of BBE encoded by the gene from Eschscholzia californica (California poppy) in the methylotrophic yeast Pichia pastoris employing the secretory pathway of the host organism. Using a two-step chromatographic purification protocol, 120 mg of BBE could be obtained from 1 liter of fermentation culture. The purified protein exhibits a turnover number for substrate conversion of 8.2 s(-1). The recombinant enzyme is glycosylated and carries a covalently attached FAD cofactor. In addition to the previously known covalent attachment of the 8alpha-position of the flavin ring system to a histidine (His-104), we could also demonstrate that a covalent linkage between the 6-position and a thiol group of a cysteine residue (Cys-166) is present in BBE. The major evidence for the occurrence of a bi-covalently attached FAD cofactor is provided by N-terminal amino acid sequencing and mass spectrometric analysis of the isolated flavin-containing peptide. Furthermore, it could be shown that anaerobic photoirradiation leads to cleavage of the linkage between the 6-cysteinyl group yielding 6-mercaptoflavin and a peptide with the cysteine residue replaced by alanine due to breakage of the C-S bond. Overall, BBE is shown to exhibit typical flavoprotein oxidase properties as exemplified by the occurrence of an anionic flavin semiquinone species and formation of a flavin N(5)-sulfite adduct.     

Heterotachy processes in rhodophyte-derived secondhand plastid genes: Implications for addressing the origin and evolution of dinoflagellate plastids

Serial transfer of plastids from one eukaryotic host to another is the key process involved in evolution of secondhand plastids. Such transfers drastically change the environment of the plastids and hence the selection regimes, presumably leading to changes over time in the characteristics of plastid gene evolution and to misleading phylogenetic inferences. About half of the dinoflagellate protists species are photosynthetic and unique in harboring a diversity of plastids acquired from a wide range of eukaryotic algae. They are therefore ideal for studying evolutionary processes of plastids gained through secondary and tertiary endosymbioses. In the light of these processes, we have evaluated the origin of 2 types of dinoflagellate plastids, containing the peridinin or 19'-hexanoyloxyfucoxanthin (19'-HNOF) pigments, by inferring the phylogeny using "covarion" evolutionary models allowing the pattern of among-site rate variation to change over time. Our investigations of genes from secondary and tertiary plastids derived from the rhodophyte plastid lineage clearly reveal "heterotachy" processes characterized as stationary covarion substitution patterns and changes in proportion of variable sites across sequences. Failure to accommodate covarion-like substitution patterns can have strong effects on the plastid tree topology. Importantly, multigene analyses performed with probabilistic methods using among-site rate and covarion models of evolution conflict with proposed single origin of the peridinin- and 19'-HNOF-containing plastids, suggesting that analysis of secondhand plastids can be hampered by convergence in the evolutionary signature of the plastid DNA sequences. Another type of sequence convergence was detected at protein level involving the psaA gene. Excluding the psaA sequence from a concatenated protein alignment grouped the peridinin plastid with haptophytes, congruent with all DNA trees. Altogether, taking account of complex processes involved in the evolution of dinoflagellate plastid sequences (both at the DNA and amino acid level), we demonstrate the difficulty of excluding independent, tertiary origin for both the peridinin and 19'-HNOF plastids involving engulfment of haptophyte-like algae. In addition, the refined topologies suggest the red algal order, Porphyridales, as the endosymbiont ancestor of the secondary plastids in cryptophytes, haptophytes, and heterokonts.     

Gq-coupled receptors as mechanosensors mediating myogenic vasoconstriction

Despite the central physiological function of the myogenic response, the underlying signalling pathways and the identity of mechanosensors in vascular smooth muscle (VSM) are still elusive. In contrast to present thinking, we show that membrane stretch does not primarily gate mechanosensitive transient receptor potential (TRP) ion channels, but leads to agonist-independent activation of G(q/11)-coupled receptors, which subsequently signal to TRPC channels in a G protein- and phospholipase C-dependent manner. Mechanically activated receptors adopt an active conformation, allowing for productive G protein coupling and recruitment of beta-arrestin. Agonist-independent receptor activation by mechanical stimuli is blocked by specific antagonists and inverse agonists. Increasing the AT(1) angiotensin II receptor density in mechanically unresponsive rat aortic A7r5 cells resulted in mechanosensitivity. Myogenic tone of cerebral and renal arteries is profoundly diminished by the inverse angiotensin II AT(1) receptor agonist losartan independently of angiotensin II (AII) secretion. This inhibitory effect is enhanced in blood vessels of mice deficient in the regulator of G-protein signalling-2. These findings suggest that G(q/11)-coupled receptors function as sensors of membrane stretch in VSM cells.