The γ-aminobutyric acid shunt contributes to closing the tricarboxylic acid cycle in Synechocystis sp. PCC 6803

Wei Xiong, Daniel Brune, Willem Vermaas

Research output: Contribution to journalArticle

46 Citations (Scopus)

Abstract

A traditional 2-oxoglutarate dehydrogenase complex is missing in the cyanobacterial tricarboxylic acid cycle. To determine pathways that convert 2-oxoglutarate into succinate in the cyanobacterium Synechocystis sp. PCC 6803, a series of mutant strains, Δsll1981, Δslr0370, Δslr1022 and combinations thereof, deficient in 2-oxoglutarate decarboxylase (Sll1981), succinate semialdehyde dehydrogenase (Slr0370), and/or in γ-aminobutyrate metabolism (Slr1022) were constructed. Like in Pseudomonas aeruginosa, N-acetylornithine aminotransferase, encoded by slr1022, was shown to also function as γ-aminobutyrate aminotransferase, catalysing γ-aminobutyrate conversion to succinic semialdehyde. As succinic semialdehyde dehydrogenase converts succinic semialdehyde to succinate, an intact γ-aminobutyrate shunt is present in Synechocystis. The Δsll1981 strain, lacking 2-oxoglutarate decarboxylase, exhibited a succinate level that was 60% of that in wild type. However, the succinate level in the Δslr1022 and Δslr0370 strains and the Δsll1981/Δslr1022 and Δsll1981/Δslr0370 double mutants was reduced to 20-40% of that in wild type, suggesting that the γ-aminobutyrate shunt has a larger impact on metabolite flux to succinate than the pathway via 2-oxoglutarate decarboxylase. <sup>13</sup>C-stable isotope analysis indicated that the γ-aminobutyrate shunt catalysed conversion of glutamate to succinate. Independent of the 2-oxoglutarate decarboxylase bypass, the γ-aminobutyrate shunt is a major contributor to flux from 2-oxoglutarate and glutamate to succinate in Synechocystis sp. PCC 6803.

Original languageEnglish (US)
Pages (from-to)786-796
Number of pages11
JournalMolecular Microbiology
Volume93
Issue number4
DOIs
StatePublished - Aug 1 2014

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2-oxoglutarate decarboxylase
Aminobutyrates
Synechocystis
Citric Acid Cycle
Succinic Acid
Succinate-Semialdehyde Dehydrogenase
Glutamic Acid
4-Aminobutyrate Transaminase
Ketoglutarate Dehydrogenase Complex
Cyanobacteria
Isotopes
Pseudomonas aeruginosa

ASJC Scopus subject areas

  • Molecular Biology
  • Microbiology
  • Medicine(all)

Cite this

The γ-aminobutyric acid shunt contributes to closing the tricarboxylic acid cycle in Synechocystis sp. PCC 6803. / Xiong, Wei; Brune, Daniel; Vermaas, Willem.

In: Molecular Microbiology, Vol. 93, No. 4, 01.08.2014, p. 786-796.

Research output: Contribution to journalArticle

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abstract = "A traditional 2-oxoglutarate dehydrogenase complex is missing in the cyanobacterial tricarboxylic acid cycle. To determine pathways that convert 2-oxoglutarate into succinate in the cyanobacterium Synechocystis sp. PCC 6803, a series of mutant strains, Δsll1981, Δslr0370, Δslr1022 and combinations thereof, deficient in 2-oxoglutarate decarboxylase (Sll1981), succinate semialdehyde dehydrogenase (Slr0370), and/or in γ-aminobutyrate metabolism (Slr1022) were constructed. Like in Pseudomonas aeruginosa, N-acetylornithine aminotransferase, encoded by slr1022, was shown to also function as γ-aminobutyrate aminotransferase, catalysing γ-aminobutyrate conversion to succinic semialdehyde. As succinic semialdehyde dehydrogenase converts succinic semialdehyde to succinate, an intact γ-aminobutyrate shunt is present in Synechocystis. The Δsll1981 strain, lacking 2-oxoglutarate decarboxylase, exhibited a succinate level that was 60{\%} of that in wild type. However, the succinate level in the Δslr1022 and Δslr0370 strains and the Δsll1981/Δslr1022 and Δsll1981/Δslr0370 double mutants was reduced to 20-40{\%} of that in wild type, suggesting that the γ-aminobutyrate shunt has a larger impact on metabolite flux to succinate than the pathway via 2-oxoglutarate decarboxylase. 13C-stable isotope analysis indicated that the γ-aminobutyrate shunt catalysed conversion of glutamate to succinate. Independent of the 2-oxoglutarate decarboxylase bypass, the γ-aminobutyrate shunt is a major contributor to flux from 2-oxoglutarate and glutamate to succinate in Synechocystis sp. PCC 6803.",
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