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Properties of succinyl-coenzyme A:D-citramalate coenzyme A transferase and its role in the autotrophic 3-hydroxypropionate cycle of Chloroflexus aurantiacus.
Friedmann, Silke; Alber, Birgit E; Fuchs, Georg.
Affiliation
  • Friedmann S; Mikrobiologie, Institut Biologie II, Schänzlestr. 1, D-79104 Freiburg, Germany.
J Bacteriol ; 188(18): 6460-8, 2006 Sep.
Article in En | MEDLINE | ID: mdl-16952935
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-CoAd-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.
Subject(s)

Full text: 1 Database: MEDLINE Main subject: Acyl Coenzyme A / Coenzyme A-Transferases / Lactic Acid / Chloroflexus / Malates Language: En Year: 2006 Type: Article

Full text: 1 Database: MEDLINE Main subject: Acyl Coenzyme A / Coenzyme A-Transferases / Lactic Acid / Chloroflexus / Malates Language: En Year: 2006 Type: Article