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The two carboxylases of Corynebacterium glutamicum essential for fatty acid and mycolic acid synthesis.

ABSTRACT: The suborder Corynebacterianeae comprises bacteria like Mycobacterium tuberculosis and Corynebacterium glutamicum, and these bacteria contain in addition to the linear fatty acids, unique alpha-branched beta-hydroxy fatty acids, called mycolic acids. Whereas acetyl-coenzyme A (CoA) carboxylase activity is required to provide malonyl-CoA for fatty acid synthesis, a new type of carboxylase is apparently additionally present in these bacteria. It activates the alpha-carbon of a linear fatty acid by carboxylation, thus enabling its decarboxylative condensation with a second fatty acid to afford mycolic acid synthesis. We now show that the acetyl-CoA carboxylase of C. glutamicum consists of the biotinylated alpha-subunit AccBC, the beta-subunit AccD1, and the small peptide AccE of 8.9 kDa, forming an active complex of approximately 812,000 Da. The carboxylase involved in mycolic acid synthesis is made up of the two highly similar beta-subunits AccD2 and AccD3 and of AccBC and AccE, the latter two identical to the subunits of the acetyl-CoA carboxylase complex. Since AccD2 and AccD3 orthologues are present in all Corynebacterianeae, these polypeptides are vital for mycolic acid synthesis forming the unique hydrophobic outer layer of these bacteria, and we speculate that the two beta-subunits present serve to lend specificity to this unique large multienzyme complex.

SUBMITTER: Gande R

PROVIDER: S-EPMC1951862 | biostudies-literature | 2007 Jul

REPOSITORIES: biostudies-literature

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The two carboxylases of Corynebacterium glutamicum essential for fatty acid and mycolic acid synthesis.

Gande Roland R Dover Lynn G LG Krumbach Karin K Besra Gurdyal S GS Sahm Hermann H Oikawa Tadao T Eggeling Lothar L

Journal of bacteriology 20070504 14

The suborder Corynebacterianeae comprises bacteria like Mycobacterium tuberculosis and Corynebacterium glutamicum, and these bacteria contain in addition to the linear fatty acids, unique alpha-branched beta-hydroxy fatty acids, called mycolic acids. Whereas acetyl-coenzyme A (CoA) carboxylase activity is required to provide malonyl-CoA for fatty acid synthesis, a new type of carboxylase is apparently additionally present in these bacteria. It activates the alpha-carbon of a linear fatty acid by ...[more]

PMID: 17483212

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Project description:To date, no information has been made available on the genetic traits that lead to increased carbon flow into the fatty acid biosynthetic pathway of Corynebacterium glutamicum. To develop basic technologies for engineering, we employed an approach that begins by isolating a fatty acid-secreting mutant without depending on mutagenic treatment. This was followed by genome analysis to characterize its genetic background. The selection of spontaneous mutants resistant to the palmitic acid ester surfactant Tween 40 resulted in the isolation of a desired mutant that produced oleic acid, suggesting that a single mutation would cause increased carbon flow down the pathway and subsequent excretion of the oversupplied fatty acid into the medium. Two additional rounds of selection of spontaneous cerulenin-resistant mutants led to increased production of the fatty acid in a stepwise manner. Whole-genome sequencing of the resulting best strain identified three specific mutations (fasR20, fasA63(up), and fasA2623). Allele-specific PCR analysis showed that the mutations arose in that order. Reconstitution experiments with these mutations revealed that only fasR20 gave rise to oleic acid production in the wild-type strain. The other two mutations contributed to an increase in oleic acid production. Deletion of fasR from the wild-type strain led to oleic acid production as well. Reverse transcription-quantitative PCR analysis revealed that the fasR20 mutation brought about upregulation of the fasA and fasB genes encoding fatty acid synthases IA and IB, respectively, by 1.31-fold ± 0.11-fold and 1.29-fold ± 0.12-fold, respectively, and of the accD1 gene encoding the ?-subunit of acetyl-CoA carboxylase by 3.56-fold ± 0.97-fold. On the other hand, the fasA63(up) mutation upregulated the fasA gene by 2.67-fold ± 0.16-fold. In flask cultivation with 1% glucose, the fasR20 fasA63(up) fasA2623 triple mutant produced approximately 280 mg of fatty acids/liter, which consisted mainly of oleic acid (208 mg/liter) and palmitic acid (47 mg/liter).

Project description:For fatty acid biosynthesis, Corynebacterium glutamicum uses two type I fatty acid synthases (FAS-I), FasA and FasB, in addition to acetyl-coenzyme A (CoA) carboxylase (ACC) consisting of AccBC, AccD1, and AccE. The in vivo roles of the enzymes in supplying precursors for biotin and ?-lipoic acid remain unclear. Here, we report genetic evidence demonstrating that the biosynthesis of these cofactors is linked to fatty acid biosynthesis through the FAS-I pathway. For this study, we used wild-type C. glutamicum and its derived biotin vitamer producer BFI-5, which was engineered to express Escherichia coli bioBF and Bacillus subtilis bioI Disruption of either fasA or fasB in strain BFI-5 led to decreased production of biotin vitamers, whereas its amplification contributed to increased production, with a larger impact of fasA in both cases. Double disruptions of fasA and fasB resulted in no biotin vitamer production. The acc genes showed a positive effect on production when amplified simultaneously. Augmented fatty acid biosynthesis was also reflected in pimelic acid production when carbon flow was blocked at the BioF reaction. These results indicate that carbon flow down the FAS-I pathway is destined for channeling into the biotin biosynthesis pathway, and that FasA in particular has a significant impact on precursor supply. In contrast, fasB disruption resulted in auxotrophy for lipoic acid or its precursor octanoic acid in both wild-type and BFI-5 strains. The phenotypes were fully complemented by plasmid-mediated expression of fasB but not fasA These results reveal that FasB plays a specific physiological role in lipoic acid biosynthesis in C. glutamicumIMPORTANCE For the de novo biosynthesis of fatty acids, C. glutamicum exceptionally uses a eukaryotic multifunctional type I fatty acid synthase (FAS-I) system comprising FasA and FasB, in contrast to most bacteria, such as E. coli and B. subtilis, which use an individual nonaggregating type II fatty acid synthase (FAS-II) system. In this study, we reported genetic evidence demonstrating that the FAS-I system is the source of the biotin precursor in vivo in the engineered biotin-prototrophic C. glutamicum strain. This study also uncovered the important physiological role of FasB in lipoic acid biosynthesis. Here, we present an FAS-I enzyme that functions in supplying the lipoic acid precursor, although its biosynthesis has been believed to exclusively depend on FAS-II in organisms. The findings obtained here provide new insights into the metabolic engineering of this industrially important microorganism to produce these compounds effectively.

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The two carboxylases of Corynebacterium glutamicum essential for fatty acid and mycolic acid synthesis.

Publications

The two carboxylases of Corynebacterium glutamicum essential for fatty acid and mycolic acid synthesis.

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