Splice variants of protein disulfide isomerase - identification, distribution and functional characterization in the rat.

BACKGROUND: Protein Disulfide Isomerase (PDI) enzyme is an emerging therapeutic target in oncology and hematology. Although PDI reductase activity has been studied with isolated fragments of the protein, natural structural variations affecting reductase activity have not been addressed. METHODS: In this study, we discovered four coding splice variants of the Pdi pre-mRNA in rats. In vitro Michaelis constants and apparent maximum steady-state rate constants after purification and distribution in different rat tissues were determined. RESULTS: The consensus sequence was found to be the most expressed splice variant while the second most expressed variant represents 15 to 35% of total Pdi mRNA. The third variant shows a quasi-null expression profile and the fourth was not quantifiable. The consensus sequence splice variant and the second splice variant are widely expressed (transcription level) in the liver and even more present in males. Measurements of the reductase activity of recombinant PDI indicate that the consensus sequence and third splice variant are fully active variants. The second most expressed variant, differing by a lack of signal peptide, was found active but less than the consensus sequence. GENERAL SIGNIFICANCE: Our work emphasizes the importance of taking splice variants into account when studying PDI-like proteins to understand the full biological functionalities of PDI.

What is a supercoiling-sensitive gene? Insights from topoisomerase I inhibition in the Gram-negative bacterium Dickeya dadantii.

DNA supercoiling is an essential mechanism of bacterial chromosome compaction, whose level is mainly regulated by topoisomerase I and DNA gyrase. Inhibiting either of these enzymes with antibiotics leads to global supercoiling modifications and subsequent changes in global gene expression. In previous studies, genes responding to DNA relaxation induced by DNA gyrase inhibition were categorised as 'supercoiling-sensitive'. Here, we studied the opposite variation of DNA supercoiling in the phytopathogen Dickeya dadantii using the non-marketed antibiotic seconeolitsine. We showed that the drug is active against topoisomerase I from this species, and analysed the first transcriptomic response of a Gram-negative bacterium to topoisomerase I inhibition. We find that the responding genes essentially differ from those observed after DNA relaxation, and further depend on the growth phase. We characterised these genes at the functional level, and also detected distinct patterns in terms of expression level, spatial and orientational organisation along the chromosome. Altogether, these results highlight that the supercoiling-sensitivity is a complex feature, which depends on the action of specific topoisomerases, on the physiological conditions, and on their genomic context. Based on previous in vitro expression data of several promoters, we propose a qualitative model of SC-dependent regulation that accounts for many of the contrasting transcriptomic features observed after DNA gyrase or topoisomerase I inhibition.

Natural-product-inspired design and synthesis of two series of compounds active against Trypanosoma cruzi: Insights into structure-activity relationship, toxicity, and mechanism of action.

Chemical scaffolds of natural products have historically been sources of inspiration for the development of novel molecules of biological relevance, including hit and lead compounds. To identify new compounds active against Trypanosoma cruzi, we designed and synthesized 46 synthetic derivatives based on the structure of two classes of natural products: tetrahydrofuran lignans (Series 1) and oxazole alkaloids (Series 2). Compounds were screened in vitro using a cellular model of T. cruzi infection. In the first series of compounds, 11 derivatives of hit compound 5 (EC50 = 1.1 µM) were found to be active; the most potent (7, 8, and 13) had EC50 values of 5.1-34.2 µM. In the second series, 17 analogs were found active at 50 µM; the most potent compounds (47, 49, 59, and 63) showed EC50 values of 24.2-49.1 µM. Active compounds were assessed for selectivity, hemocompatibility, synergistic potential, effects on mitochondrial membrane potential, and inhibitory effect on trypanothione reductase. All active compounds showed low toxicity against uninfected THP-1 cells and human erythrocytes. The potency of compounds 5 and 8 increased steadily in combination with benznidazole, indicating a synergistic effect. Furthermore, compounds 8, 47, 49, 59, and 63 inhibited parasitic mitochondria in a dose-dependent manner. Although increased reactive oxygen species levels might lead to mitochondrial effects, the results indicate that the mechanism of action of the compounds is not dependent on trypanothione reductase inhibition. In silico calculation of chemical descriptors and principal component analysis showed that the active compounds share common chemical features with other trypanocidal molecules and are predicted to have a good ADMET profile. Overall, the results suggest that the compounds are important candidates to be further studied for their potential against T. cruzi.

A Continuous and Sensitive Spectrophotometric Assay for Lipase and Phospholipase A Activities Using α-Eleostearic Acid-Containing Substrates.

To date, several sensitive methods, based on radiolabeled elements or sterically hindered fluorochrome groups, are usually employed to screen lipase and phospholipase A (PLA) activities. Here, a new ultraviolet spectrophotometric assay for lipase or PLA was developed using natural triglycerides or synthetic glycerophosphatidylcholines containing α-eleostearic acid (9Z, 11E, 13E-octadecatrienoic acid) purified from Aleurites fordii seed oil. The conjugated triene present in α-eleostearic acid constitutes an intrinsic chromophore and consequently confers strong UV absorption properties of this free fatty acid as well as of lipid substrates harboring it. The substrate was coated into the wells of a microplate, and the lipolytic activities were measured by the absorbance increase at 272 nm due to the transition of α-eleostearic acid moiety from the adsorbed to the soluble state. This continuous assay is compatible with a high-throughput screening method and can be applied specifically to the screening of new potential lipase, PLA1 and PLA2 inhibitors.

Synthesis of new dicinnamoyl 4-deoxy quinic acid and methyl ester derivatives and evaluation of the toxicity against the pea aphid Acyrthosiphon pisum.

New dicinnamoyl (caffeoyl, feruloyl, ortho and para-coumaroyl) 4-deoxyquinic acid and esters were synthesized by using a new 4-deoxy quinic acid triol intermediate. The optimisation of both coupling and deprotection steps allowed the preparation in good yields of the target products either as the carboxylic acid or the methyl ester form. Eight new compounds were evaluated for their ability to influence the feeding behaviour of the pea aphid Acyrthosiphon pisum. Artificial diet bioassays showed that two compounds are toxic (mortality and growth inhibition) at lower concentrations than the reference 3,5-dicaffeoyl quinic acid.

Development of a high-throughput assay for measuring phospholipase A activity using synthetic 1,2-α-eleostearoyl-sn-glycero-3-phosphocholine coated on microtiter plates.

To date, several sensitive methods, based on radiolabeled elements or sterically hindered fluorochrome groups, are usually employed to screen phospholipase A (PLA) activities. With the aim of developing a convenient, specific, sensitive, and continuous new ultraviolet (UV) spectrophotometric assay for PLA, we have synthesized a specific glycerophosphatidylcholine (PC) esterified at the sn-1 and sn-2 positions, with α-eleostearic acid (9Z, 11E, 13E-octadecatrienoic acid) purified from Aleurites fordii seed oil. The conjugated triene present in α-eleostearic acid constitutes an intrinsic chromophore and, consequently, confers the strong UV absorption properties of this free fatty acid as well as of the glycerophospholipids harboring it. This coated PC film cannot be desorbed by the various buffers used during PLA assays. Following the action of PLA at the oil-water interface, α-eleostearic acid is freed and desorbed from the film and then solubilized with ß-cyclodextrin. The UV absorbance of the α-eleostearic acid is considerably enhanced due to the transformation from an adsorbed to a water-soluble state. The PLA activity can be measured continuously by recording the variations with time of the UV absorption spectra. The rate of lipolysis was monitored by measuring the increase of absorption at 272 nm, which was found to be linear with time and proportional to the amount of added PLA. This continuous high-throughput PLA assay could be used to screen new PLA and/or PLA inhibitors present in various biological samples.

Synthesis and biological evaluation of new N-acyl-homoserine-lactone analogues, based on triazole and tetrazole scaffolds, acting as LuxR-dependent quorum sensing modulators.

New analogues of N-acyl-homoserine-lactone (AHL), in which the amide was replaced by a triazole or tetrazole ring, were prepared and tested for their activity as LuxR-dependent QS modulators. Several compounds showed a level of antagonistic or agonistic activity, notably some 1,4-triazolic and 1,5-tetrazolic derivatives, whereas the 2,5-tetrazolic compounds were inactive. In 1,5-tetrazoles, substituted with butyrolactone and an alkyl chain, the activity was reversed, depending on the connection between the lactone and the tetrazole. The C-N connected compounds were agonists whereas the C-C connected ones were antagonists.