Complexes and Complexities of the Citric Acid Cycle in Escherichia coli

Guest, John R.; Russell, George C.

doi:10.1016/b978-0-12-152833-1.50018-6

Cited by 53 publications

(35 citation statements)

References 32 publications

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“…Excretion of alanine but not glutamate has been detected for bacteroids from peas and soybeans (Appels & Haaker, 1991;Kouchi et al, 1991;Rosendahl et al, 1992). The pyruvate dehydrogenase complex has strong structural and functional similarities to the 2-oxoglutarate dehydrogenase complex (Miles & Guest, 1987;Guest & Russell, 1992), and its inhibition by a low redox potential, as has been suggested for the 2-oxoglutarate dehydrogenase complex, might lead to the accumulation of pyruvate or its transamination product alanine. Labelling studies with pea bacteroids incubated in malate show a rapid rise in intracellular glutamate, followed by a smaller rise in alanine (Salminen & Streeter, 1992).…”

Section: Discussionmentioning

confidence: 99%

“…In other bacteria, sucA and sucD are clustered with genes encoding other TCA cycle enzymes (Miles & Guest, 1987;Nicholls et al, 1990;Nishiyama et al, 1991;Guest, 1992;Guest & Russell, 1992). It was therefore anticipated that several R. leguminosarum TCA cycle genes might be carried by pRU3004, in addition to sucA and sucD.…”

Section: Structure Of the Mdh-suc Operonmentioning

confidence: 99%

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Regulation of the TCA cycle and the general amino acid permease by overflow metabolism in Rhizobium leguminosarum

et al. 1997

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Reading RG6 6AJ, UKMutants of Rhizobium leguminosarum were selected that were altered in the uptake activity of the general amino acid permease (Aap). The main class of mutant maps to s u d and suct), which are part of a gene cluster mdh-sucCDAB, which codes for malate dehydrogenase (mdh), succinyl-CoA synthetase (sucCD) and components of the 2-oxoglutarate dehydrogenase complex ( s u d B ) . Mutation of either SUCC or SUCD prevents expression of 2-oxoglutarate dehydrogenase (sucAB). Conversely, mutation of sucA or sucB results in much higher levels of succinyl-CoA synthetase and malate dehydrogenase activity. These results suggest that the genes mdh-sucCDAB may constitute an operon. suc mutants, unlike the wild-type, excrete large quantities of glutamate and 2-oxoglutarate. Concomitant with mutation of s u d or suct), the intracellular concentration of glutamate but not 2-oxoglutarate was highly elevated, suggesting that 2-oxoglutarate normally feeds into the glutamate pool. Elevation of the intracellular glutamate pool appeared to be coupled to glutamate excretion as part of an overflow pathway for regulation of the TCA cycle. Amino acid uptake via the Aap of R. leguminosamm was strongly inhibited in the suc mutants, even though the transcription level of the aap operon was the same as the wild-type. This is consistent with previous observations that the Aap, which influences glutamate excretion in R. leguminosarum, has uptake inhibited when excretion occurs. Another class of mutant impaired in uptake by the Aap is mutated in polyhydroxybutyrate synthase (phaC). Mutants of succinyl-CoA synthetase (SUCD) or 2-oxoglutarate dehydrogenase (sucA) form ineffective nodules. However, mutants of aap, which are unable to grow on glutamate as a carbon source in laboratory culture, show wild-type levels of nitrogen fixation. This indicates that glutamate is not an important carbon and energy source in the bacteroid. Instead glutamate synthesis, like polyhydroxybutyrate synthesis, appears to be a sink for carbon and reductant, formed when the 2-oxoglutarate dehydrogenase complex is blocked. This is in accord with previous observations that bacteroids synthesize high concentrations of glutamate. Overall the data show that the TCA cycle in R. leguminosarum is regulated by amino acid excretion and polyhydroxybutyrate biosynthesis which act as overflow pathways for excess carbon and reductant.

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Section: Discussionmentioning

confidence: 99%

Section: Structure Of the Mdh-suc Operonmentioning

confidence: 99%

Regulation of the TCA cycle and the general amino acid permease by overflow metabolism in Rhizobium leguminosarum

et al. 1997

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“…It is now apparent from studies with the corresponding lac2 fusions that the fumA promoter resembles PacnB in being anaerobically repressed by ArcA, whereas the fumC promoter resembles P2acnA in its dual regulation by ArcA and FNR, although there is evidence that fumC transcription is partially facilitated by readthrough from the upstream fumA gene promoter (Woods & Guest, 1987;Guest & Russell, 1992;Gruer & Guest, 1994;Park & Gunsalus, 1995). The relationship is further strengthened by showing that the genes (fumc and acnA) encoding the minor aerobic enzymes are alone activated by SoxRS and a38.…”

Section: Regulation Of Acnb Gene Transcriptionmentioning

confidence: 99%

Transcriptional regulation of the aconitase genes (acnA and acnB) of Escherichia coli

1997

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Escherichia coli contains two differentially regulated aconitase genes, acnA and acnB. Two acnA promoters transcribing from start points located 407 bp (PIacnA) and 50 bp (PZacnA) upstream of the acnA coding region, and one acnB promoter (Pa,,) with a start point 95 bp upstream of the acnB coding region, were identified by primer extension analysis. A 2.8 kb acnA monocistronic transcript was detected by Northern blot hybridization, but only in redoxstressed (methyl-viologen-treated) cultures, and a 2.5 kb acnB monocistronic transcript was detected in exponential-but not stationary-phase cultures. These findings are consistent with previous observations that acnA is specifically subject to SoxRS-mediated activation, whereas acnB encodes the major aconitase that is synthesized earlier in the growth cycle than AcnA. Further studies with acn-lac2 gene fusions and a wider range of transcription regulators indicated that acnA expression is initiated by G~~ from PIacnA, and from PZacnA it is activated directly or indirectly by CRP, FruR, Fur and SoxRS, and repressed by ArcA and FNR. In contrast, acnB expression is activated by CRP and repressed by ArcA, FruR and Fis from PacnB. Comparable studies with fum-laczfusions indicated that transcription of fumC, but not of fumA or fumB, is initiated by RNA polymerase containing G~~. It is concluded that AcnB is the major citric acid cycle enzyme, whereas AcnA is an aerobic stationaryphase enzyme that is specifically induced by iron and redox-stress.Keywords : aconitase, fumarase, citric acid cycle genes, transcription regulation, global regulators INTRODUCTION Aconitase (EC 4 . 2 . 1 . 3 ) catalyses the reversible isomerization of citrate and isocitrate via cis-aconitate in the citric acid cycle. It is a monomeric enzyme containing an unstable [4Fe-4S] cluster which is reversibly converted to an inactive [3Fe-4S] form (Beinert et al., 1996). The aconitase protein family contains aconitases, isopropylmalate isomerases and homoaconitases from diverse sources, and the iron-dependent regulatory proteins (IRP) which regulate either the translation or the stabilities of specific vertebrate mRNAs (Klausner & Rouault, 1993;Frishman & Hentze, 1996;Hentze & Kuhn, 1996 ;Gruer et al., 1997a). The bifunctional IRPl proteins, which operate either as cytoplasmic aconitases or as site-specific RNA-binding proteins depending on the reversible incorporation or disruption of the iron-sulphur clusters, are particularly interesting. A structural archetype for all members of this family is provided by the porcine mitochondria1 aconitase (Robbins & Stout, 1989). The basic structure contains three structural domains, tightly packed around the iron-sulphur cluster, that are located beneath a deep active-site cleft and the upper (fourth) domain. However, three different domain arrangements have now been recognized (Gruer et al., 1997a). In most cases domain four is at the C-terminal end, connected to the rest of the molecule by a long linker, but in some bacterial aconitases (notably AcnB of Escherichi...

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“…Instead, it is activated by metabolic intermediates such as a high AMP/ATP ratio (139). In E. coli, the expression of the KDH is upregulated during aerobic growth but is highly repressed during fermentative growth (68). This repression results in a branched TCA "cycle" which generates the biosynthetic precursor ␣-ketoglutarate through an oxidative branch and succinyl-CoA through a reductive branch (215).…”

Section: Lipoylated Complexesmentioning

confidence: 99%

Lipoic Acid Metabolism in Microbial Pathogens

Spalding

Prigge

2010

Microbiol Mol Biol Rev

164

204

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SUMMARY Lipoic acid [(R)-5-(1,2-dithiolan-3-yl)pentanoic acid] is an enzyme cofactor required for intermediate metabolism in free-living cells. Lipoic acid was discovered nearly 60 years ago and was shown to be covalently attached to proteins in several multicomponent dehydrogenases. Cells can acquire lipoate (the deprotonated charge form of lipoic acid that dominates at physiological pH) through either scavenging or de novo synthesis. Microbial pathogens implement these basic lipoylation strategies with a surprising variety of adaptations which can affect pathogenesis and virulence. Similarly, lipoylated proteins are responsible for effects beyond their classical roles in catalysis. These include roles in oxidative defense, bacterial sporulation, and gene expression. This review surveys the role of lipoate metabolism in bacterial, fungal, and protozoan pathogens and how these organisms have employed this metabolism to adapt to niche environments.

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Complexes and Complexities of the Citric Acid Cycle in Escherichia coli

Cited by 53 publications

References 32 publications

Regulation of the TCA cycle and the general amino acid permease by overflow metabolism in Rhizobium leguminosarum

Regulation of the TCA cycle and the general amino acid permease by overflow metabolism in Rhizobium leguminosarum

Transcriptional regulation of the aconitase genes (acnA and acnB) of Escherichia coli

Lipoic Acid Metabolism in Microbial Pathogens

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