Properties of Succinyl-Coenzyme A:D-citramalate Coenzyme A Transferase and Its Role in the Autotrophic 3-hydroxypropionate Cycle of Chloroflexus Aurantiacus

J Bacteriol. 2006 Sep;188(18):6460-8. doi: 10.1128/JB.00659-06.

Abstract

The phototrophic bacterium Chloroflexus aurantiacus uses the 3-hydroxypropionate cycle for autotrophic CO(2) fixation. This cycle starts with acetyl-coenzyme A (CoA) and produces glyoxylate. Glyoxylate is an unconventional cell carbon precursor that needs special enzymes for assimilation. Glyoxylate is combined with propionyl-CoA to beta-methylmalyl-CoA, which is converted to citramalate. Cell extracts catalyzed the succinyl-CoA-dependent conversion of citramalate to acetyl-CoA and pyruvate, the central cell carbon precursor. This reaction is due to the combined action of enzymes that were upregulated during autotrophic growth, a coenzyme A transferase with the use of succinyl-CoA as the CoA donor and a lyase cleaving citramalyl-CoA to acetyl-CoA and pyruvate. Genomic analysis identified a gene coding for a putative coenzyme A transferase. The gene was heterologously expressed in Escherichia coli and shown to code for succinyl-CoA:d-citramalate coenzyme A transferase. This enzyme, which catalyzes the reaction d-citramalate + succinyl-CoA --> d-citramalyl-CoA + succinate, was purified and studied. It belongs to class III of the coenzyme A transferase enzyme family, with an aspartate residue in the active site. The homodimeric enzyme composed of 44-kDa subunits was specific for succinyl-CoA as a CoA donor but also accepted d-malate and itaconate instead of d-citramalate. The CoA transferase gene is part of a cluster of genes which are cotranscribed, including the gene for d-citramalyl-CoA lyase. It is proposed that the CoA transferase and the lyase catalyze the last two steps in the glyoxylate assimilation route.

MeSH terms

  • Acyl Coenzyme A / metabolism*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / physiology
  • Binding Sites / genetics
  • Chloroflexus / enzymology*
  • Chloroflexus / genetics
  • Chloroflexus / metabolism
  • Cloning, Molecular
  • Coenzyme A-Transferases / genetics
  • Coenzyme A-Transferases / isolation & purification
  • Coenzyme A-Transferases / metabolism*
  • Dimerization
  • Escherichia coli / genetics
  • Gene Expression
  • Genes, Bacterial
  • Lactic Acid / analogs & derivatives*
  • Lactic Acid / metabolism
  • Malates / metabolism*
  • Molecular Weight
  • Multigene Family
  • Protein Subunits
  • RNA, Bacterial / analysis
  • RNA, Messenger / analysis
  • Recombinant Proteins / biosynthesis
  • Recombinant Proteins / isolation & purification
  • Substrate Specificity
  • Succinates / metabolism
  • Transcription, Genetic

Substances

  • Acyl Coenzyme A
  • Bacterial Proteins
  • Malates
  • Protein Subunits
  • RNA, Bacterial
  • RNA, Messenger
  • Recombinant Proteins
  • Succinates
  • Lactic Acid
  • succinyl-coenzyme A
  • malic acid
  • hydracrylic acid
  • Coenzyme A-Transferases
  • citramalate
  • itaconic acid