Properties of succinyl-coenzyme A:D-citramalate coenzyme A transferase and its role in the autotrophic 3-hydroxypropionate cycle of Chloroflexus aurantiacus.
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.
Friedmann
Silke
S
Mikrobiologie, Institut Biologie II, Schänzlestr. 1, D-79104 Freiburg, Germany.
Alber
Birgit E
BE
Fuchs
Georg
G
D000214:Acyl Coenzyme A / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology; D001665:Binding Sites / Q000235:genetics; D041861:Chloroflexus / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D015256:Coenzyme A-Transferases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D005798:Genes, Bacterial; D019344:Lactic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D008293:Malates / Q000378:metabolism*; D008970:Molecular Weight; D005810:Multigene Family; D021122:Protein Subunits; D012329:RNA, Bacterial / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000302:isolation & purification; D013379:Substrate Specificity; D013386:Succinates / Q000378:metabolism; D014158:Transcription, Genetic
D000214:Acyl Coenzyme A; D001426:Bacterial Proteins; D008293:Malates; D021122:Protein Subunits; D012329:RNA, Bacterial; D012333:RNA, Messenger; D011994:Recombinant Proteins; D013386:Succinates; D019344:Lactic Acid; C030298:malic acid; C012046:succinyl-coenzyme A; C031601:hydracrylic acid; D015256:Coenzyme A-Transferases; C011729:citramalate; C005229:itaconic acid