Gotowa bibliografia na temat „Argininosuccinate Lyase (ArgH)”

In methicillin-sensitive Staphylococcus aureus (MSSA), the tricarboxylic acid (TCA) cycle is known to negatively regulate production of the major biofilm-matrix exopolysaccharide, PIA/PNAG. However, methicillin-resistant S. aureus (MRSA) produce a primarily proteinaceous biofilm matrix, and contribution of the TCA-cycle therein remains unclear. Utilizing USA300-JE2 Tn-mutants (NARSA) in genes encoding TCA- and urea cycle enzymes for transduction into a prolific biofilm-forming USA300 strain (UAS391-Erys), we studied the contribution of the TCA- and urea cycle and of proteins, eDNA and PIA/PNAG, to the matrix. Genes targeted in the urea cycle encoded argininosuccinate lyase and arginase (argH::Tn and rocF::Tn), and in the TCA-cycle encoded succinyl-CoA synthetase, succinate dehydrogenase, aconitase, isocitrate dehydrogenase, fumarate hydratase class II, and citrate synthase II (sucC::Tn, sdhA/B::Tn, acnA::Tn, icd::Tn, fumC::Tn and gltA::Tn). Biofilm formation was significantly decreased under no flow and flow conditions by argH::Tn, fumC::Tn, and sdhA/B::Tn (range OD492 0.374−0.667; integrated densities 2.065−4.875) compared to UAS391-EryS (OD492 0.814; integrated density 10.676) (p ≤ 0.008). Cellular and matrix stains, enzymatic treatment (Proteinase K, DNase I), and reverse-transcriptase PCR-based gene-expression analysis of fibronectin-binding proteins (fnbA/B) and the staphylococcal accessory regulator (sarA) on pre-formed UAS391-Erys and Tn-mutant biofilms showed: (i) < 1% PIA/PNAG in the proteinaceous/eDNA matrix; (ii) increased proteins under no flow and flow in the matrix of Tn mutant biofilms (on average 50 and 51 (±11)%) compared to UAS391-Erys (on average 22 and 25 (±4)%) (p < 0.001); and (iii) down- and up-regulation of fnbA/B and sarA, respectively, in Tn-mutants compared to UAS391-EryS (0.62-, 0.57-, and 2.23-fold on average). In conclusion, we show that the biofilm matrix of MRSA-USA300 and the corresponding Tn mutants is PIA/PNAG-independent and are mainly composed of proteins and eDNA. The primary impact of TCA-cycle inactivation was on the protein component of the biofilm matrix of MRSA-USA300.

ABSTRACT Cyanophycin (multi-l-arginyl-poly-l-aspartic acid; also known as cyanophycin grana peptide [CGP]) is a putative precursor for numerous biodegradable technically used chemicals. Therefore, the biosynthesis and production of the polymer in recombinant organisms is of special interest. The synthesis of cyanophycin derivatives consisting of a wider range of constituents would broaden the applications of this polymer. We applied recombinant Saccharomyces cerevisiae strains defective in arginine metabolism and expressing the cyanophycin synthetase of Synechocystis sp. strain PCC 6308 in order to synthesize CGP with citrulline and ornithine as constituents. Strains defective in arginine degradation (Car1 and Car2) accumulated up to 4% (wt/wt) CGP, whereas strains defective in arginine synthesis (Arg1, Arg3, and Arg4) accumulated up to 15.3% (wt/wt) of CGP, which is more than twofold higher than the previously content reported in yeast and the highest content ever reported in eukaryotes. Characterization of the isolated polymers by different analytical methods indicated that CGP synthesized by strain Arg1 (with argininosuccinate synthetase deleted) consisted of up to 20 mol% of citrulline, whereas CGP from strain Arg3 (with ornithine carbamoyltransferase deleted) consisted of up to 8 mol% of ornithine, and CGP isolated from strain Arg4 (with argininosuccinate lyase deleted) consisted of up to 16 mol% lysine. Cultivation experiments indicated that the incorporation of citrulline or ornithine is enhanced by the addition of low amounts of arginine (2 mM) and also by the addition of ornithine or citrulline (10 to 40 mM), respectively, to the medium.

Restriction enzyme-mediated integration (REMI) mutagenesis was used to tag genes required for pathogenicity of Fusarium oxysporum f. sp. melonis. Of the 1,129 REMI transformants tested, 13 showed reduced pathogenicity on susceptible melon cultivars. One of the mutants, FMMP95–1, was an arginine auxotroph. Structural analysis of the tagged site in FMMP95-1 identified a gene, designated ARG1, which possibly encodes argininosuccinate lyase, catalyzing the last step for arginine biosynthesis. Complementation of FMMP95–1 with the ARG1 gene caused a recovery in pathogenicity, indicating that arginine auxotrophic mutation causes reduced pathogenicity in this pathogen.

Despite significant improvements in treatment and survival in paediatric cancers, outcomes for children with brain tumours remain poor. Novel therapeutic approaches are needed to improve survival and quality of survival. Extracellular arginine dependency (auxotrophy) has been recognised in several tumours as a potential therapeutic target. This dependency is due to the inability of cancer cells to recycle or synthesise intracellular arginine through the urea cycle pathway compared to normal cells. Whilst adult glioblastoma exhibits this dependency, the expression of the arginine pathway enzymes has not been delineated in paediatric brain tumours. We used immunohistochemical (IHC) methods to stain for arginine pathway enzymes in paediatric high-grade glioma (pHGG), low-grade glioma (pLGG), ependymoma (EPN), and medulloblastoma (MB) tumour tissue microarrays (TMAs). The antibodies detected protein expression of the metaboliser arginase (Arg1 and Arg2); recycling enzymes ornithine transcarbamoylase (OTC), argininosuccinate synthetase (ASS1), and argininosuccinate lyase (ASL); and the transporter SLC7A1. Deficiency of OTC, ASS1, and ASL was seen in 87.5%, 94%, and 79% of pHGG samples, respectively, consistent with an auxotrophic signature. Similar result was obtained in pLGG with 96%, 93%, and 91% of tumours being deficient in ASL, ASS1, and OTC, respectively. 79%, 88%, and 85% of MB cases were ASL, ASS1, and OTC deficient whilst ASL and OTC were deficient in 57% and 91% of EPN samples. All tumour types highly expressed SLC7A1 and Arginase, with Arg2 being the main isoform, demonstrating that they could transport and utilise arginine. Our results show that pHGG, pLGG, EPN, and MB demonstrate arginine auxotrophy based on protein expression and are likely to be susceptible to arginine depletion. Pegylated arginase (BCT-100) is currently in phase I/II trials in relapsed pHGG. Our results suggest that therapeutic arginine depletion may also be useful in other tumour types and IHC analysis of patient tumour samples could help identify patients likely to benefit from this treatment.

Abstract We have established a high-efficiency method for transforming the unicellular, green alga Chlamydomonas reinhardtii by electroporation. Electroporation of strains CC3395 and CC425, cell wall-less mutants devoid of argininosuccinate lyase (encoded by ARG7), in the presence of the plasmid pJD67 (which contains ARG7) was used to optimize conditions for the introduction of exogenous DNA. The conditions that were varied included osmolarity, temperature, concentration of exogenous DNA, voltage and capacitance. Following optimization, the maximum transformation frequency obtained was 2 × 105 transformants per μg of DNA; this frequency is two orders of magnitude higher than obtained with the current standard method using glass beads to introduce exogenous DNA. The electroporation procedure described in this article is of general utility, and makes it feasible to isolate genes by direct complementation of Chlamydomonas reinhardtii mutants.

The argininosuccinate lyase activity of duck delta-crystallin was inactivated by diethyl pyrocarbonate at 0 degrees C and pH 7.5. The inactivation followed pseudo-first-order kinetics after appropriate correction for the decomposition of the reagent during the modification period. The plot of the observed pseudo-first-order rate constant versus diethyl pyrocarbonate concentration in the range of 0.17-1.7 mM was linear and went through the origin with a second-order rate constant of 1.45 +/- 0.1 M-1.s-1. The double-logarithmic plot was also linear, with slope of 1.13, which suggested a 1:1 stoichiometry for the reaction between diethyl pyrocarbonate and delta-crystallin. L-Arginine, L-norvaline or L-citrulline protected the argininosuccinate lyase activity of delta-crystallin from diethyl pyrocarbonate inactivation. The dissociation constants for the delta-crystallin-L-arginine and delta-crystallin-L-citrulline binary complexes, determined by the protection experiments, were 4.2 +/- 0.2 and 0.12 +/- 0.04 mM respectively. Fumarate alone had no protective effect. However, fumarate plus L-arginine gave synergistic protection with a ligand binding interacting factor of 0.12 +/- 0.02. The double-protection data conformed to a random Uni Bi kinetic mechanism. Fluorescence-quenching studies indicated that the modified delta-crystallin had minimum, if any, conformational changes as compared with the native delta-crystallin. Inactivation of the enzyme activity was accompanied by an increasing absorbance at 240 nm of the protein. The absorption near 280 nm did not change. Treatment of the modified protein with hydroxylamine regenerated the enzyme activity to the original level. These results strongly indicated the modification of an essential histidine residue. Calculation from the 240 nm absorption changes indicated that only one histidine residue per subunit was modified by the reagent. This super-active histidine residue has a pKa value of approximately 6.8 and acts as a general acid-base catalyst in the enzyme reaction mechanism. Our experimental data are compatible with an E1cB mechanism [Raushel (1984) Arch. Biochem. Biophys. 232, 520-525] for the argininosuccinate lyase with the essential histidine residue close to the arginine-binding domain of delta-crystallin. L-Citrulline, after binding to this domain, might form an extra hydrogen bond with the essential histidine residue.

Tuberculosis (TB) is a deadly disease responsible for the death of approximately 1.5 million people each year, with the highest being from developing nations. Tuberculosis affects mostly the lungs, and other parts of the body like nerves, bones and liver. Mycobacterium tuberculosis (Mtb) is the causative agent of TB in humans. The onset of infection is via the deposition of aerosol droplets containing the pathogen, M. tuberculosis, onto the lung alveolar surfaces. About one third of the world’s population asymptomatically harbors latent M. tuberculosis bacterium with a constant risk of disease activation. Due to the emergence of drug-resistant strains and the evolution through multi-drug resistance (MDR) to extensive drug resistance (XDR), the fight against TB has become extremely challenging. Standard treatment for TB comprises four first-line antimicrobials: isoniazid, rifampicin, pyrazinamide and ethambutol. However, resistance to all of these drugs has been observed in several MDR strains of Mtb. Despite the recent advances in target identification and drug discovery, there is a relentless need for novel inhibitors against vital pathways of Mtb. The novel drug-development regimens endorse strategies wherein the pre-approved drugs for other ailments could be re-purposed, thereby cutting down the cost and time associated with the process of drug discovery. Also, the target selection strategy requires to aim at the key enzymes from the essential biosynthetic pathways, keeping an eye on their underlying dissimilarities when compared to human host. The challenges in finding a suitable target for anti-Mtb drug discovery is it’s ever evolving stride and the conserved nature of the essential proteins. Many novel small molecule inhibitors of Mtb are undermined, during the course of studies, by cross reactivity with homologs proteins in the host. Traditionally, the replication machinery has been at the heart of drug discovery and the processes associated with logarithmic growth phase are vastly exploited for drug targeting. However, targeting these vital cellular components may result in some serious non-specific effects to the host. On the other hand, the intricate network of metabolic pathways provides novel avenues for specific targeting of pathogens, precisely for three main reasons: 1. There is an acute shortage of cellular nutrients due to the constant competition between the pathogen and the host, throughout the course of infection. 2. Infectious cycles often lead to the disruption of metabolic pathways, again leading to nutrient scarcity. 3. Survival of the pathogen within the hostile niche and under oxygen starvation conditions further potentiate the demands of crucial metabolites (amino acids, nitrogen bases, carbohydrates etc.) that are used as the building blocks for cellular machinery. 4. Metabolic pathways have evolved with time, to provide the much-required specificity for exclusive targeting of the pathogen, thereby limiting the cross-reactivity with the host pathways. In order to persist and efficiently replicate in host cells, intracellular pathogens must adapt their metabolism to the available nutrients and physical conditions (mainly pH, oxygen availability and osmotic pressure) in the host. Among the major metabolic, amino acid metabolism holds great importance; as they not only serve to meet the nutritional needs of the pathogen but also play a key role in the strategies employed during pathogenesis. Although the host and the pathogen compete for many metabolites, three amino acids, Arginine, Asparagine and Tryptophan seems to be a focus of this competition because the availability of these amino acids or their derivatives influence both pathogen behavior and the immune response. Arginine constitutes a major proportion of the total proteins in the cell and arginine and its precursor ornithine are used for the biosynthesis of the most common polyamines, putrescine and spermidine. These molecules are required for optimal growth of the organism and are involved in several physiological processes. Apart from being a critical amino acid for the synthesis of cellular proteins, arginine can also be used as a nitrogen source, under conditions of nitrogen starvation, hence crucial for pathogenesis. The glutamate and glutamine are the key metabolites in the central nitrogen metabolism; both serve as endogenous nitrogen acceptor as well as nitrogen donor. However, reports demonstrate that Mtb utilizes arginine and asparagine as the key sources of nitrogen during infection in mice models of tuberculosis. Therefore, our study focuses on the process of Arginine biosynthesis in M. tuberculosis, wherein it is essential for the survival and pathogenesis. Since the arginine metabolism is essential for both the host and the pathogen, and competition for arginine may shift the balance, and thus determine the outcome of the infection. The enzymes involved in this pathway will be a promising target for anti-TB drug development. Despite the acknowledged significance of Arginine biosynthesis in the pathogens like M. tuberculosis, inhibitors to target this pathway remain to be discovered. Moreover, inhibitors of this pathway may provide novel insights to the significance of arginine biosynthesis in Mtb associated stress responses and persistence. Ornithine acetyltransferase (MtArgJ), one of the crucial enzymes during the biosynthesis of arginine in Mtb, is essential for its survival and pathogenesis. MtArgJ lacks a homolog in human genome, thereby being a good target against Mtb. We hypothesize that a targeted inhibitor against this key player of mycobacterial metabolism has the potential to combat the Mtb survival and pathogenesis. In the present thesis, we have characterized the potential of MtArgJ from M. tuberculosis as a valuable target for drug design against tuberculosis. Most importantly, the approach is to specifically target a novel allosteric site identified in this study, on the MtArgJ surface. Since we are not using the age-old approach of substrate analog as an inhibitor, we hereby further minimize or even eliminate the chances of cross-reactivity with the host cellular proteins. In the later parts, we have identified an allosteric inhibitor of MtArgJ, that significantly reduces the survival of pathogenic Mtb through the pre-clinical models of tuberculosis. Chapter 1 of this thesis gives a detailed account of the history of Tuberculosis, and its pathogenesis. The chapter further elaborates on the metabolic pathways of Mycobacterium tuberculosis, with special emphasis on the arginine biosynthesis pathway. The drug discovery regime and therapeutic challenges associated with the disease are discussed in the later parts of the chapter. All the information discussed in this chapter serves a preface for the work done throughout the thesis, and outlinesthe objectives for rest of the chapters. Chapter 2 describes the characterization and kinetic analysis of MtArgH, the last enzyme from the arginine biosynthetic pathway in M. tuberculosis. This chapter demonstrates the importance of a c-terminal cysteine residue (Cys441) in the catalysis and thermal stability of the enzyme. We further propose the existence of a product mediated feed-back inhibition of MtArgH, wherein fumarate, one of the product of MtArgH, gradually modifies the Cys441 through succination. Chapter 3 to 5 discuss about the work carried out on the enzyme Ornithine acetyltransferase (MtArgJ), a crucial enzyme for arginine biosynthesis in M. tuberculosis. We have identified a selective allosteric inhibitor against this key player of mycobacterial metabolism, employing the below-mentioned strategy. First step was to characterize the target, followed by a structure based in-silico screen. The best hits were subjected to in-vitro validation, leading to the in-vivo testing of the potential molecule, in the pre-clinical model of tuberculosis. Target characterization In-silico screen In-vitro validation Pre-clinical testing Chapter 3 starts with the characterization of the MtArgJ, wherein we identified a novel hydrophobic pocket present on the enzyme surface. We further characterized the potential of this pocket in allosterically modulating the active site. This was then followed by a structure based in-silico screen with a library of FDA approved drugs, specifically targeting this novel allosteric pocket on MtArgJ. Chapter 4 deals with the in vitro validation of the identified compounds from in-silico screen. We here identified two lead molecules, Pranlukast (PRK) and Sorafenib (SRB), to have significant affinity for the allosteric site on MtArgJ, leading to the inhibition of its enzymatic activity. We further propose the key residues involved in this interaction, thereby suggesting a potential molecular mechanism of inhibition. Chapter 5 leads us to the in-vitro and in-vivo characterization of these compounds as a potent anti-tubercular agent. We first demonstrate its efficacy in deducing the survival of the pathogenic strains of Mtb in-vitro and in the macrophage models of infection. We also tested the efficacy of these compounds in combination with the standard of care TB therapy drugs, and found PRK to work efficiently in such combinations. Finally, we evidence the potency of PRK in compromising the survival and pathogenesis of Mtb in mice models of tuberculosis infection. PRK is presently being used as a drug against chronic asthma, therefore its human safety is already assured. This will facilitate its induction into the direct clinical trials against tuberculosis. Taken together, the work done in this thesis demonstrates a novel metabolic inhibitor of Mtb pathogenesis, through the pre-clinical models of infection with the potential for development of advanced combinatorial therapy against tuberculosis.