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Modulation of the arginase pathway in the context of microbial pathogenesis: a metabolic enzyme moonlighting as an immune modulator.

ABSTRACT: Arginine is a crucial amino acid that serves to modulate the cellular immune response during infection. Arginine is also a common substrate for both inducible nitric oxide synthase (iNOS) and arginase. The generation of nitric oxide from arginine is responsible for efficient immune response and cytotoxicity of host cells to kill the invading pathogens. On the other hand, the conversion of arginine to ornithine and urea via the arginase pathway can support the growth of bacterial and parasitic pathogens. The competition between iNOS and arginase for arginine can thus contribute to the outcome of several parasitic and bacterial infections. There are two isoforms of vertebrate arginase, both of which catalyze the conversion of arginine to ornithine and urea, but they differ with regard to tissue distribution and subcellular localization. In the case of infection with Mycobacterium, Leishmania, Trypanosoma, Helicobacter, Schistosoma, and Salmonella spp., arginase isoforms have been shown to modulate the pathology of infection by various means. Despite the existence of a considerable body of evidence about mammalian arginine metabolism and its role in immunology, the critical choice to divert the host arginine pool by pathogenic organisms as a survival strategy is still a mystery in infection biology.

SUBMITTER: Das P

PROVIDER: S-EPMC2887468 | biostudies-other | 2010

REPOSITORIES: biostudies-other

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Project description:Most available knowledge on fungal arginine metabolism is derived from studies on Saccharomyces cerevisiae, in which arginine catabolism is initiated by releasing urea via the arginase reaction. Orthologs of the S. cerevisiae genes encoding the first three enzymes in the arginase pathway were cloned from Kluyveromyces lactis and shown to functionally complement the corresponding deletion in S. cerevisiae. Surprisingly, deletion of the single K. lactis arginase gene KlCAR1 did not completely abolish growth on arginine as nitrogen source. Growth rate of mutant strongly increased during serial transfer in shake-flask cultures. A combination of RNAseq-based transcriptome analysis and 13C-15N-based flux analysis was used to elucidate the arginase-independent pathway. Isotopic 13C15N-enrichment in ?-aminobutyrate revealed succinate as the entry point in the TCA cycle of the alternative pathway. Transcript analysis combined with enzyme activity measurements indicated increased expression in the Klcar1? mutant of a guanidinobutyrase (EC.3.5.3.7), an enzyme not previously demonstrated in fungi. Expression of the K. lactis KLLA0F27995g (renamed KlGBU1) encoding guanidinobutyrase enabled S. cerevisiae to use guanidinobutyrate as sole nitrogen source and its deletion in K. lactis almost completely abolish growth on this nitrogen source. Phylogenetic analysis suggests that this enzyme activity is widespread in fungi. The goal of the present study was to characterize arginine catabolism in K. lactis. To this end, CAR1, CAR2 and PRO3 orthologs in K. lactis were identified and functionally analysed by deletion, expression in S. cerevisiae and enzyme activity assays. Since deletion of the arginase gene in K. lactis was found not to completely abolish growth on arginine as a sole nitrogen source, the alternative pathway for arginine catabolism operating in this yeast was studied by a combination of transcriptome analysis, 13C and 15N isotope-based flux analysis and enzyme activity assays in cell extracts. To investigate arginine metabolism in the arginase-negative K. lactis strain, strains GG1632 (Klku80? KlCAR1 reference strain) and IMS0367 (Klcar1? Arg+) were grown in aerobic bioreactor batch cultures on glucose chemically defined medium with arginine as sole nitrogen source. RNA sequencing of samples taken during the exponential phase of growth on glucose-arginine media of the reference strain G1631 and the arginase less strain IMS0367 were compared resulting in the characterization of a new function.

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Modulation of the arginase pathway in the context of microbial pathogenesis: a metabolic enzyme moonlighting as an immune modulator.

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