Two phenotypically compensating isocitrate dehydrogenases inRalstonia eutropha

Abstract

The tricarboxylic acid (TCA) cycle enzyme isocitrate dehydrogenase (IDH) and the glyoxylate bypass enzyme isocitrate lyase are involved in catabolism of isocitrate and play a key role in controlling the metabolic flux between the TCA cycle and the glyoxylate shunt. Two IDH genes icd1 and icd2 of Ralstonia eutropha HF39, encoding isocitrate dehydrogenase 1 (IDH1) and isocitrate dehydrogenase 2 (IDH2), were identified and characterized. Icd1 was functionally expressed in Escherichia coli, whereas icd2 was expressed in E. coli but no activity was obtained. Interposon-mutants of icd1 (HF39vicd1) and icd2 (HF39vicd2) of R. eutropha HF39 were constructed and their phenotypes were investigated. HF39vicd1 retained 43% of IDH activity, which was not induced by acetate, and HF39vicd2 expressed 74% of acetate-induced IDH activity. Both HF39vicd1and HF39vicd2 kept the same growth rate on acetate as the wild-type. These data suggested that IDH1 is induced by acetate. The interposon-mutants HF39vicd1 and HF39vicd2 accumulated the same amount of poly(3-hydroxybutyric acid) as the wild-type.

Two isocitrate dehydrogenases from a plant pathogen Xanthomonas campestris pv. campestris 8004. Bioinformatic analysis, enzymatic characterization, and implication in virulence

“…The evolutionary distance between the two IDH isozymes from one bacterium reveals the complexity of the ancient IDH protein family. The phenomenon of the coexistence of two different IDH isozymes in one bacterium has been reported from previous studies . Two structurally different dimeric and monomeric types of IDH isozymes were confirmed to exist in the psychrophilic bacteria C .…”

“…It was revealed that the expression of the NADP + ‐specific IDH1 (48 kDa) of R . eutropha was induced by acetate, while the other NADP + ‐specific IDH2 (83 kDa) in this bacterium was constitutively expressed . Deletion of either of these two IDHs didn't affect the R .…”

“…Deletion of either of these two IDHs didn't affect the R . eutropha 's growth on gluconate or acetate, suggesting that the two IDHs are phenotypically compensated . Similarly, the expression of the C. maris IDH1 was induced by acetate, while the C. maris IDH2 was induced by low temperature .…”

“…Although the facts that one bacterium owned two IDHs have been reported repeatedly , the physiological significance of IDH coexistence in bacteria has not been completely understood. It was revealed that the expression of the NADP + ‐specific IDH1 (48 kDa) of R .…”

“…Since both XccIDH1 and XccIDH2 work efficiently in vitro, it will be interesting to ask what different roles they play in bacterial cell. Although the facts that one bacterium owned two IDHs have been reported repeatedly [8][9][10]26], the physiological significance of IDH coexistence in bacteria has not been completely understood. It was revealed that the expression of the NADP þ -specific IDH1 (48 kDa) of R. eutropha was induced by acetate, while the other NADP þspecific IDH2 (83 kDa) in this bacterium was constitutively expressed [10].…”