Academic literature on the topic 'Arginine Biosynthesis Pathway'

Ornithine decarboxylase (ODC) catalyzes the first step in the polyamine biosynthetic pathway, a highly regulated pathway in which activity increases during rapid growth. Other enzymes also metabolize ornithine, and in hepatomas, rate of growth correlates with decreased activity of these other enzymes, which thus channels more ornithine to polyamine biosynthesis. Ornithine is produced from arginase cleavage of arginine, which also serves as the precursor for nitric oxide production. To study whether short-term coordination of ornithine and arginine metabolism exists in rat colon, ODC, ornithine aminotransferase (OAT), arginase, ornithine, arginine, and polyamine levels were measured after two stimuli (refeeding and/or deoxycholate exposure) known to synergistically induce ODC activity. Increased ODC activity was accompanied by increased putrescine levels, whereas OAT and arginase activity were reduced by either treatment, accompanied by an increase in both arginine and ornithine levels. These results indicate a rapid reciprocal change in ODC, OAT, and arginase activity in response to refeeding or deoxycholate. The accompanying increases in ornithine and arginine concentration are likely to contribute to increased flux through the polyamine and nitric oxide biosynthetic pathways in vivo.

Abstract Arginine is an amino acid critical for various cellular processes, not only protein synthesis but also metabolism of other essential metabolites, like polyamines, as well as a signaling factor for pathways such as the growth regulator mTOR. Previously, our group measured arginine levels in the interstitial fluid of tumors (TIF) of pancreatic ductal adenocarcinoma (PDAC) murine models and found extremely low arginine levels (2-5 uM) in the tumor microenvironment (TME). Despite near complete absence of this critical nutrient in the TME, pancreatic tumors exhibit aggressive growth. We have sought to understand both how the PDAC TME becomes arginine limited and how PDAC cells adapt to proliferate in the absence of arginine. Using genetically engineered mice, we find that arginase activity in the myeloid compartment of PDAC tumors is responsible for arginine depletion in the TME. Staining of Arg1+ myeloid populations in human PDAC samples suggest a similar mechanism reduces arginine availability in human PDAC tumors as well. We then leveraged our newfound knowledge of PDAC TIF composition to develop a novel ex vivo cell culture media formulation with physiologically relevant nutrient levels and monitored arginine acquisition pathways using isotope tracing and metabolomics assays to determine how PDAC cells cope with arginine deprivation. Under TME nutrient conditions, PDAC cells consume available citrulline and use it to produce arginine by de novo synthesis. Starving cells of citrulline or genetically perturbing arginosuccinate synthase (ASS1), key enzyme in arginine biosynthesis, significantly reduces PDAC cellular arginine and proliferative capacity. Immunohistochemical analysis of both human and mouse PDAC tumors indicates that the de novo arginine synthesis pathway is highly expressed in PDAC but not in untransformed pancreas, suggesting a key role for this pathway in PDAC progression. Altogether, we find that myeloid-derived arginase challenges PDAC cells by limiting arginine availability and suggest that de novo arginine synthesis may be a critical metabolic pathway that enables PDAC tumors to cope with this metabolic challenge. Citation Format: Juan Apiz-Saab, Alex Muir. Myeloid-derived arginase depletes microenvironmental arginine in PDAC tumors and leads to activation of arginine de novo biosynthesis in cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2177.

ABSTRACT The biosynthesis of carbamoylphosphate is catalyzed by the heterodimeric enzyme carbamoylphosphate synthetase. The genes encoding the two subunits of this enzyme in procaryotes are normally transcribed as an operon, but the gene encoding the large subunit (carB) in Lactococcus lactis is shown to be transcribed as an isolated unit. Carbamoylphosphate is a precursor in the biosynthesis of both pyrimidine nucleotides and arginine. By mutant analysis,L. lactis is shown to possess only onecarB gene; the same gene product is thus required for both biosynthetic pathways. Furthermore, arginine may satisfy the requirement for carbamoylphosphate in pyrimidine biosynthesis through degradation by means of the arginine deiminase pathway. The expression of the carB gene is subject to regulation at the level of transcription by pyrimidines, most probably by an attenuator mechanism. Upstream of the carB gene, an open reading frame showing a high degree of similarity to those of glutathione peroxidases from other organisms was identified.

Reactive oxygen species (ROS)-mediated oxidative stress and DNA damage have recently been recognized as contributing to the efficacy of most bactericidal antibiotics, irrespective of their primary macromolecular targets. Inhibitors of targets involved in both combating oxidative stress as well as being required for in vivo survival may exhibit powerful synergistic action. This study demonstrates that the de novo arginine biosynthetic pathway in Mycobacterium tuberculosis (Mtb) is up-regulated in the early response to the oxidative stress-elevating agent isoniazid or vitamin C. Arginine deprivation rapidly sterilizes the Mtb de novo arginine biosynthesis pathway mutants ΔargB and ΔargF without the emergence of suppressor mutants in vitro as well as in vivo. Transcriptomic and flow cytometry studies of arginine-deprived Mtb have indicated accumulation of ROS and extensive DNA damage. Metabolomics studies following arginine deprivation have revealed that these cells experienced depletion of antioxidant thiols and accumulation of the upstream metabolite substrate of ArgB or ArgF enzymes. ΔargB and ΔargF were unable to scavenge host arginine and were quickly cleared from both immunocompetent and immunocompromised mice. In summary, our investigation revealed in vivo essentiality of the de novo arginine biosynthesis pathway for Mtb and a promising drug target space for combating tuberculosis.

Absract Several enzymes involved in polyamine biosynthesis namely ornithine, arginine and S-adenosylmethionine decarboxylase as well as spermidine synthase, were analyzed in partially purified wheat extracts. For all enzymes effective inhibitors were found. Among them the most interesting was l-aminooxy-3-aminopropane, which inhibited all three decarboxylases. Classical polyamine biosynthesis inhibitors like difluoromethylornithine, difluoromethylarginine. methyl glyoxal bis- (guanylhydrazone) and cyclohexylamine were also inhibitory on plant enzymes. A remarkable difference in the amount of arginine and ornithine decarboxylase existed in wheat. Arginine decarboxylase seems to be more important at least during the early stage of development. Influence of polyamine synthesis inhibitors on polyamine levels is more likely to come from arginine decarboxylase inhibitors. As inhibitors of all essential enzymes involved in plant polyamine biosynthesis were found, the study of the importance of polyamines in plant physiology will be considerably facilitated.

Arginine biosynthetic genes from Campylobacter jejuni TGH9011 were cloned by functional complementation of the respective Escherichia coli arginine biosynthetic mutants. Complementation of argA, argB, argC, argD, argE, argF, and argH auxotrophs was accomplished using a pBR322-based C. jejuni TGH9011 plasmid library. By cross-complementation analyses, the first four steps of arginine biosynthesis were shown to be closely linked on the genome. Two additional clones complementing the first (ArgA) and fifth (ArgE) steps in arginine biosynthesis were obtained. Neither recombinant showed linkage to the arg cluster, to each other, nor to other arginine biosynthetic functions by cross-complementation. Genes argF and argH were not linked to other arginine biosynthetic genes by cross-complementation analysis. Restriction enzyme patterns of recombinant plasmids fell into five groups. Group I contained the arg(ABCD) complementing locus. Group II and Group III were the two genetic loci corresponding to the argA and argE complementing genes. Group II contains the hipO gene encoding N-benzoylglycine-amino-acid amidohydrolase, also known as hippurate hydrolase. Group III contains the hipO homolog of C. jejuni. Group IV represents the argF gene. GroupV is the argH gene. Functional complementation of mutations in the first four steps of the arginine biosynthetic pathway was obtained on recombinant plasmid pARGC2. The predicted order of gene complementation was argCargA(argBargD). The sequence of the insert in plasmid pARGC2 revealed direct homologs for argC, argB, and argD. However, sequence analysis of the gene complementing ArgA function in two separate E. coli argA mutants determined that the C. jejuni gene was not a canonical argA gene. The gene complementing the argA defect, which we call argO, showed limited homology to the streptothricin acetyltransferase gene (sat) of Escherichia coli. The flanking open reading frames in pARGC2 showed no homologies to arginine biosynthetic genes. The structure of the argCOBD gene arrangement is discussed with reference to the presence and location of other arginine biosynthetic genes on the genome of C. jejuni and other bacterial organisms.Key words: arginine synthesis, Campylobacter jejuni, arginine biosynthetic genes, gene sequence, gene arrangement.

l-Ornithine decarboxylase provides de novo putrescine biosynthesis in mammals. Alternative pathways to generate putrescine that involve ADC (l-arginine decarboxylase) occur in non-mammalian organisms. It has been suggested that an ADC-mediated pathway may generate putrescine via agmatine in mammalian tissues. Published evidence for a mammalian ADC is based on (i) assays using mitochondrial extracts showing production of 14CO2 from [1-14C]arginine and (ii) cloned cDNA sequences that have been claimed to represent ADC. We have reinvestigated this evidence and were unable to find any evidence supporting a mammalian ADC. Mitochondrial extracts prepared from freshly isolated rodent liver and kidney using a metrizamide/Percoll density gradient were assayed for ADC activity using l-[U-14C]-arginine in the presence or absence of arginine metabolic pathway inhibitors. Although 14CO2 was produced in substantial amounts, no labelled agmatine or putrescine was detected. [14C]Agmatine added to liver extracts was not degraded significantly indicating that any agmatine derived from a putative ADC activity was not lost due to further metabolism. Extensive searches of current genome databases using non-mammalian ADC sequences did not identify a viable candidate ADC gene. One of the putative mammalian ADC sequences appears to be derived from bacteria and the other lacks several residues that are essential for decarboxylase activity. These results indicate that 14CO2 release from [1-14C]arginine is not adequate evidence for a mammalian ADC. Although agmatine is a known constituent of mammalian cells, it can be transported from the diet. Therefore l-ornithine decarboxylase remains the only established route for de novo putrescine biosynthesis in mammals.

DcsB, one of the enzymes encoded in the D-cycloserine (D-CS) biosynthetic gene cluster, displays a high sequence homology to arginase, which contains two manganese ions in the active site. However, DcsB hydrolyzes N ω-hydroxy-L-arginine, but not L-arginine, to supply hydroxyurea for the biosynthesis of D-CS. Here, the crystal structure of DcsB was determined at a resolution of 1.5 Å using anomalous scattering from the manganese ions. In the crystal structure, DscB generates an artificial dimer created by the open and closed forms. Gel-filtration analysis demonstrated that DcsB is a monomeric protein, unlike arginase, which forms a trimeric structure. The active center containing the binuclear manganese cluster differs between DcsB and arginase. In DcsB, one of the ligands of the MnA ion is a cysteine, while the corresponding residue in arginase is a histidine. In addition, DcsB has no counterpart to the histidine residue that acts as a general acid/base during the catalytic reaction of arginase. The present study demonstrates that DcsB has a unique active site that differs from that of arginase.

ABSTRACT Saxitoxin (STX) and its analogues cause the paralytic shellfish poisoning (PSP) syndrome, which afflicts human health and impacts coastal shellfish economies worldwide. PSP toxins are unique alkaloids, being produced by both prokaryotes and eukaryotes. Here we describe a candidate PSP toxin biosynthesis gene cluster (sxt) from Cylindrospermopsis raciborskii T3. The saxitoxin biosynthetic pathway is encoded by more than 35 kb, and comparative sequence analysis assigns 30 catalytic functions to 26 proteins. STX biosynthesis is initiated with arginine, S-adenosylmethionine, and acetate by a new type of polyketide synthase, which can putatively perform a methylation of acetate, and a Claisen condensation reaction between propionate and arginine. Further steps involve enzymes catalyzing three heterocyclizations and various tailoring reactions that result in the numerous isoforms of saxitoxin. In the absence of a gene transfer system in these microorganisms, we have revised the description of the known STX biosynthetic pathway, with in silico functional inferences based on sxt open reading frames combined with liquid chromatography-tandem mass spectrometry analysis of the biosynthetic intermediates. Our results indicate the evolutionary origin for the production of PSP toxins in an ancestral cyanobacterium with genetic contributions from diverse phylogenetic lineages of bacteria and provide a quantum addition to the catalytic collective available for future combinatorial biosyntheses. The distribution of these genes also supports the idea of the involvement of this gene cluster in STX production in various cyanobacteria.

Both non-arginine-depleted and arginine-depleted pulmonary artery endothelial cells (PAEC) actively convert citrulline into arginine. Exposure to hypoxia for 4-24 h inhibited arginine synthesis from citrulline in intact cells and in cell homogenates. The conversion of L-citrulline to L-argininosuccinate by argininosuccinate synthetase (AS) was inhibited by exposure to hypoxia for 4, 12, or 24 h. The conversion of argininosuccinate to arginine by argininosuccinate lyase was inhibited by exposure to hypoxia for 24 h but not for 4-12 h. The decrease of L-arginine biosynthesis during hypoxia coincided with the increase of intracellular glutamine content and was abrogated by preventing an increase in intracellular glutamine. In addition, AS activity was inversely related to glutamine content in the medium. These results indicate that hypoxia inhibited the L-arginine biosynthetic pathway via decreased activity of AS. The latter is related to increased glutamine content. Hypoxic inhibition of arginine synthesis from citrulline did not result in a decrease of arginine content, suggesting that PAEC are able to maintain intracellular arginine for up to 24 h despite reduction in the L-arginine biosynthetic pathway.

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.

The porphyrias are a remarkable family of metabolic disorders characterized biochemically by overproduction of haem precursors, principally in the liver and bone marrow. The acute porphyrias are inborn errors of varying penetrance that affect enzymatic steps in a tightly regulated biosynthetic pathway for haem; nonacute acquired forms also occur in genetically predisposed individuals. Clinical presentation of acute porphyria—life-threatening neurovisceral attacks occur in four of the porphyrias: acute intermittent porphyria, variegate porphyria, hereditary coproporphyria, and Doss’ porphyria (5-aminolaevulinate dehydratase deficiency). These present with abdominal pain, psychiatric symptoms, and signs of sympathetic and hypothalamic autonomic overactivity, sometimes accompanied by convulsions and motor and sensory deficits. Diagnosis of acute porphyria—this is key to survival of an acute attack of porphyria, which can be suspected on the basis of the past history, in particular of photosensitivity or the intermittent discoloration of urine, and family history, and is confirmed by finding excess water-soluble haem precursors in urine. Management of acute porphyria—treatment of an acute porphyric attack mandates immediate withdrawal of inappropriate drugs and other precipitating factors; infusions of haem arginate or other licensed preparations of haem shorten life-threatening episodes and may be effective prophylaxis for recurrent porphyria in women with periodic attacks. The nonacute porphyrias are photosensitivity syndromes caused by excess photoactive macrocyclic porphyrins triggered especially by visible light in the blue–violet range. In the most severe form, manifestations are of severe blistering lesions on sun-exposed skin, particularly of the hands and face, with the formation of vesicles and bullae that may become infected. Healing may lead to loss of digits, scarring of the eyelids, nose, lips, and scalp, and occasionally blindness due to corneal scarring.