Regulation of Salmonella typhimurium ilvYC genes

Blazey, D L; Burns, R. O.

doi:10.1128/jb.159.3.951-957.1984

Cited by 10 publications

(3 citation statements)

References 22 publications

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“…Ketol acid reductoisomerase activity is expected to reflect intracellular levels of the acetohydroxy acids acetolactate and acetohydroxybutyrate, since the expression of ilvC is induced by these compounds (6,55,60,74). However, strains TV493 and TV503, which are completely devoid of AHAS activity and hence are unable to synthesize the inducing acetohydroxy acids, had levels of ketol acid reductoisomerase only twofold lower than the highest levels observed with other strains.…”

Section: Nutritional Requirements and Growth Properties Of The S Typmentioning

confidence: 97%

Branched-Chain Amino Acid Biosynthesis in Salmonella typhimurium : a Quantitative Analysis

et al. 1998

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We report here the first quantitative study of the branched-chain amino acid biosynthetic pathway in Salmonella typhimurium LT2. The intracellular levels of the enzymes of the pathway and of the 2-keto acid intermediates were determined under various physiological conditions and used for estimation of several of the fluxes in the cells. The results led to a revision of previous ideas concerning the way in which multiple acetohydroxy acid synthase (AHAS) isozymes contribute to the fitness of enterobacteria. In wild-type LT2, AHAS isozyme I provides most of the flux to valine, leucine, and pantothenate, while isozyme II provides most of the flux to isoleucine. With acetate as a carbon source, a strain expressing AHAS II only is limited in growth because of the low enzyme activity in the presence of elevated levels of the inhibitor glyoxylate. A strain with AHAS I only is limited during growth on glucose by the low tendency of this enzyme to utilize 2-ketobutyrate as a substrate; isoleucine limitation then leads to elevated threonine deaminase activity and an increased 2-ketobutyrate/2-ketoisovalerate ratio, which in turn interferes with the synthesis of coenzyme A and methionine. The regulation of threonine deaminase is also crucial in this regard. It is conceivable that, because of fundamental limitations on the specificity of enzymes, no single AHAS could possibly be adequate for the varied conditions that enterobacteria successfully encounter.

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Section: Nutritional Requirements and Growth Properties Of The S Typmentioning

confidence: 97%

Branched-Chain Amino Acid Biosynthesis in Salmonella typhimurium : a Quantitative Analysis

et al. 1998

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“…To identify essential domains or residues of the enzyme that participate in metal ion cofactor binding, the predicted amino acid sequences of plant acetohydroxy acid isomer-oreductase have been aligned to the known sequences of corresponding enzymes from fungi (Petersen & Holmberg, 1986;Sista & Bowman, 1992) and bacteria (Blazey & Bums, 1984; Wek & Hatfield, 1986;Aguilar & Grasso, 1991;Godon et al, 1992;Rieble & Beale, 1992) (Figure 2). This sequence comparison indicated five regions of identity that have been designated in this paper as domains I-V. Domain I is similar to the fingerprint region of the NADPH-binding site found in a large number of NADPH-dependent oxidoreductases (Dumas et al, 1991).…”

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confidence: 99%

Evidence for two catalytically different magnesium-binding sites in acetohydroxy acid isomeroreductase by site-directed mutagenesis

Dumas¹,

Butikofer²,

Job³

et al. 1995

Biochemistry

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Alignment of procaryotic and plant acetohydroxy acid isomeroreductase (EC 1.1.1.86) reveals five conserved regions designated domains I, II, III, IV, and V. Domain I has been previously proposed to correspond to the NADPH-binding site [Dumas et al. (1991) Biochem. J. 277, 469-475] and domain III to a putative magnesium-binding site [Sista & Bowman (1992) Gene 120, 115-118]. The binding and the function of this cation are of particular importance. First, Mg2+ is essential for the two-step reaction catalyzed by this enzyme: an isomerization followed by an NADPH-dependent reduction. Second, the plant acetohydroxy acid isomeroreductase exhibits Kd and Km values for Mg2+ of 5 microM and 6 microM, respectively. Such values correspond to the strongest affinity known between an enzyme and the metal ion. To determine if domain III of acetohydroxy acid isomeroreductase is effectively involved in magnesium binding, and with the goal to assign a function to the other conserved domains, site-directed mutagenesis was performed on each charged or polar conserved amino acids of domains II-V of the spinach acetohydroxy acid isomeroreductase. The results demonstrate that mutation of each of these amino acids leads to a partial or complete inactivation of enzyme activity. Steady-state kinetic analysis and equilibrium binding experiments show that both domains III and IV are directly involved in the binding of magnesium. Also, they suggest that magnesium bound to domain III plays a role in the reductive half-reaction, whereas, magnesium bound to domain IV is involved in the isomerization half-reaction.

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“…Most of our biochemical knowledge concerning acetohydroxy acid isomeroreductase come from studies conducted with purified prokaryotic enzymes (Arfin and Umbarger, 1969;Shematek et al, 1973;Hofler et al, 1975;Chunduru et al, 1989;Aulabaugh and Schloss, 1990). Detailed molecular analyses have described the isolation ofgenes encoding this enzyme from several prokaryotes (Blazey and Burns, 1984;Wek and Hatfield, 1986;Aguilar and Grasso, 1991;Godon et al, 1992, Rieble-and Beale, 1992) and only from a few eukaryotes, such as Saccharomyces cerevisiae (baker's yeast) (Petersen and Holmberg, 1986) and the fungus Neurospora crassa (Sista and Bowman, 1992). Such studies have led to greater insights into the structure-function relationship of this enzyme.…”

Section: Introductionmentioning

confidence: 99%

Branched-chain-amino-acid biosynthesis in plants: molecular cloning and characterization of the gene encoding acetohydroxy acid isomeroreductase (ketol-acid reductoisomerase) from Arabidopsis thaliana (thale cress)

Dumas

Curien

DeRose

et al. 1993

Biochemical Journal

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Towards the goal of gaining a better understanding of the molecular mechanisms controlling branched-chain-amino-acid biosynthesis in plants, we have isolated, sequenced and characterized a gene encoding acetohydroxy acid isomero-reductase (ketol-acid reductoisomerase) from Arabidopsis thaliana (thale cress). Comparison between the acetohydroxy acid isomeroreductase cDNA and the genomic sequence has allowed us to determine the exon structure of the coding region. The isolated acetohydroxy acid isomeroreductase gene is distributed over approx. 4.5 kbp and contains nine introns (79-347 bp). The transcriptional start site was found to be 52 bp upstream of the translational initiation site. Southern-blot analysis of A. thaliana genomic DNA shows that the acetohydroxy acid isomeroreductase is encoded by a single-copy gene.

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Regulation of Salmonella typhimurium ilvYC genes

Cited by 10 publications

References 22 publications

Branched-Chain Amino Acid Biosynthesis in Salmonella typhimurium : a Quantitative Analysis

Branched-Chain Amino Acid Biosynthesis in Salmonella typhimurium : a Quantitative Analysis

Evidence for two catalytically different magnesium-binding sites in acetohydroxy acid isomeroreductase by site-directed mutagenesis

Branched-chain-amino-acid biosynthesis in plants: molecular cloning and characterization of the gene encoding acetohydroxy acid isomeroreductase (ketol-acid reductoisomerase) from Arabidopsis thaliana (thale cress)

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