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The essential mycobacterial genes, fabG1 and fabG4, encode 3-oxoacyl-thioester reductases that are functional in yeast mitochondrial fatty acid synthase type 2.

Gurvitz A - Mol. Genet. Genomics (2009)

Bottom Line: Mycobacterial FASII undertakes mycolic acid biosynthesis, which relies on a set of essential enzymes, including 3-oxoacyl-AcpM reductase FabG1/Rv1483.Thereafter, FabG2-FabG5 were expressed as mitochondrial proteins in the oar1Delta strain, and FabG4 was found to complement the mutant phenotype and contain high levels of 3-oxoacyl-thioester reductase activity.Hence, like FabG1, FabG4 is also an essential, physiologically functional 3-oxoacyl-thioester reductase, albeit the latter's involvement in mycobacterial FASII remains to be explored.

View Article: PubMed Central - PubMed

Affiliation: Section of Physiology of Lipid Metabolism, Institute of Physiology, Center for Physiology, Pathophysiology and Immunology, Medical University of Vienna, Schwarzspanierstrasse 17, Vienna 1090, Austria. aner.gurvitz@meduniwien.ac.at

ABSTRACT
Mycobacterium tuberculosis represents a severe threat to human health worldwide. Therefore, it is important to expand our knowledge of vital mycobacterial processes, such as that effected by fatty acid synthase type 2 (FASII), as well as to uncover novel ones. Mycobacterial FASII undertakes mycolic acid biosynthesis, which relies on a set of essential enzymes, including 3-oxoacyl-AcpM reductase FabG1/Rv1483. However, the M. tuberculosis genome encodes four additional FabG homologs, designated FabG2-FabG5, whose functions have hitherto not been characterized in detail. Of the four candidates, FabG4/Rv0242c was recently shown to be essential for the survival of M. bovis BCG. The present work was initiated by assessing the suitability of yeast oar1Delta mutant cells lacking mitochondrial 3-oxoacyl-ACP reductase activity to act as a surrogate system for expressing FabG1/MabA directed to the mitochondria. Mutant yeast cells producing this targeted FabG1 variant were essentially wild type for all of the chronicled phenotype characteristics, including respiratory growth on glycerol medium, cytochrome assembly and lipoid acid production. This indicated that within the framework of de novo fatty acid biosynthesis in yeast mitochondria, FabG1 was able to act on shorter (C(4)) acyl substrates than was previously proposed (C(8-20)) during mycolic acid biosynthesis in M. tuberculosis. Thereafter, FabG2-FabG5 were expressed as mitochondrial proteins in the oar1Delta strain, and FabG4 was found to complement the mutant phenotype and contain high levels of 3-oxoacyl-thioester reductase activity. Hence, like FabG1, FabG4 is also an essential, physiologically functional 3-oxoacyl-thioester reductase, albeit the latter's involvement in mycobacterial FASII remains to be explored.

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Homology study of M. tuberculosis FabG proteins. Multalin- and Genedoc-based comparison of the deduced amino acid sequence of FabG1 (Rv1483) with those of its homologs FabG2 (Rv1350), FabG3 (Rv2002), FabG4 (Rv0242c) and FabG5 (Rv2766c). Dashes indicate the arrangement of the sequences for best fit, and arrows point to the amino acids forming the catalytic triad (Marrakchi et al. 2002). The first 150 amino acid residues of FabG4 do not match any of those of the other homologs, and were removed from the figure. Black shadings refer to strictly conserved amino acid residues among all the sequences, whereas the darker and lighter grayshadings denote regions with more relaxed residue similarities not necessarily shared by the full set of sequences
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Fig1: Homology study of M. tuberculosis FabG proteins. Multalin- and Genedoc-based comparison of the deduced amino acid sequence of FabG1 (Rv1483) with those of its homologs FabG2 (Rv1350), FabG3 (Rv2002), FabG4 (Rv0242c) and FabG5 (Rv2766c). Dashes indicate the arrangement of the sequences for best fit, and arrows point to the amino acids forming the catalytic triad (Marrakchi et al. 2002). The first 150 amino acid residues of FabG4 do not match any of those of the other homologs, and were removed from the figure. Black shadings refer to strictly conserved amino acid residues among all the sequences, whereas the darker and lighter grayshadings denote regions with more relaxed residue similarities not necessarily shared by the full set of sequences

Mentions: In M. tuberculosis FASII, FabG1 (MabA) undertakes the reduction of 3-oxoacyl-acyl carrier protein (AcpM) to generate 3-hydroxyacyl-AcpM (Banerjee et al. 1998), whereas in the equivalent mitochondrial process in Saccharomyces cerevisiae, this step is catalyzed by Oar1p (Schneider et al. 1997). In reference to substrate specificities, FabG1 has been demonstrated previously to catalyze the NADP(H)-specific reduction of long-chain (C8–20) 3-oxoacyl-thioester species. Molecular modeling of FabG1 revealed a large substrate-binding pocket capable of accommodating long-chain substrates (Marrakchi et al. 2002), while yeast Oar1p is presumed to act on only short-chain ones. Analysis of the complete sequence of the M. tuberculosis genome (Cole et al. 1998) revealed FabG1 as having four homologs, termed FabG2–FabG5 (Fig. 1), but, so far, not one of them has been fully characterized.Fig. 1


The essential mycobacterial genes, fabG1 and fabG4, encode 3-oxoacyl-thioester reductases that are functional in yeast mitochondrial fatty acid synthase type 2.

Gurvitz A - Mol. Genet. Genomics (2009)

Homology study of M. tuberculosis FabG proteins. Multalin- and Genedoc-based comparison of the deduced amino acid sequence of FabG1 (Rv1483) with those of its homologs FabG2 (Rv1350), FabG3 (Rv2002), FabG4 (Rv0242c) and FabG5 (Rv2766c). Dashes indicate the arrangement of the sequences for best fit, and arrows point to the amino acids forming the catalytic triad (Marrakchi et al. 2002). The first 150 amino acid residues of FabG4 do not match any of those of the other homologs, and were removed from the figure. Black shadings refer to strictly conserved amino acid residues among all the sequences, whereas the darker and lighter grayshadings denote regions with more relaxed residue similarities not necessarily shared by the full set of sequences
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2746893&req=5

Fig1: Homology study of M. tuberculosis FabG proteins. Multalin- and Genedoc-based comparison of the deduced amino acid sequence of FabG1 (Rv1483) with those of its homologs FabG2 (Rv1350), FabG3 (Rv2002), FabG4 (Rv0242c) and FabG5 (Rv2766c). Dashes indicate the arrangement of the sequences for best fit, and arrows point to the amino acids forming the catalytic triad (Marrakchi et al. 2002). The first 150 amino acid residues of FabG4 do not match any of those of the other homologs, and were removed from the figure. Black shadings refer to strictly conserved amino acid residues among all the sequences, whereas the darker and lighter grayshadings denote regions with more relaxed residue similarities not necessarily shared by the full set of sequences
Mentions: In M. tuberculosis FASII, FabG1 (MabA) undertakes the reduction of 3-oxoacyl-acyl carrier protein (AcpM) to generate 3-hydroxyacyl-AcpM (Banerjee et al. 1998), whereas in the equivalent mitochondrial process in Saccharomyces cerevisiae, this step is catalyzed by Oar1p (Schneider et al. 1997). In reference to substrate specificities, FabG1 has been demonstrated previously to catalyze the NADP(H)-specific reduction of long-chain (C8–20) 3-oxoacyl-thioester species. Molecular modeling of FabG1 revealed a large substrate-binding pocket capable of accommodating long-chain substrates (Marrakchi et al. 2002), while yeast Oar1p is presumed to act on only short-chain ones. Analysis of the complete sequence of the M. tuberculosis genome (Cole et al. 1998) revealed FabG1 as having four homologs, termed FabG2–FabG5 (Fig. 1), but, so far, not one of them has been fully characterized.Fig. 1

Bottom Line: Mycobacterial FASII undertakes mycolic acid biosynthesis, which relies on a set of essential enzymes, including 3-oxoacyl-AcpM reductase FabG1/Rv1483.Thereafter, FabG2-FabG5 were expressed as mitochondrial proteins in the oar1Delta strain, and FabG4 was found to complement the mutant phenotype and contain high levels of 3-oxoacyl-thioester reductase activity.Hence, like FabG1, FabG4 is also an essential, physiologically functional 3-oxoacyl-thioester reductase, albeit the latter's involvement in mycobacterial FASII remains to be explored.

View Article: PubMed Central - PubMed

Affiliation: Section of Physiology of Lipid Metabolism, Institute of Physiology, Center for Physiology, Pathophysiology and Immunology, Medical University of Vienna, Schwarzspanierstrasse 17, Vienna 1090, Austria. aner.gurvitz@meduniwien.ac.at

ABSTRACT
Mycobacterium tuberculosis represents a severe threat to human health worldwide. Therefore, it is important to expand our knowledge of vital mycobacterial processes, such as that effected by fatty acid synthase type 2 (FASII), as well as to uncover novel ones. Mycobacterial FASII undertakes mycolic acid biosynthesis, which relies on a set of essential enzymes, including 3-oxoacyl-AcpM reductase FabG1/Rv1483. However, the M. tuberculosis genome encodes four additional FabG homologs, designated FabG2-FabG5, whose functions have hitherto not been characterized in detail. Of the four candidates, FabG4/Rv0242c was recently shown to be essential for the survival of M. bovis BCG. The present work was initiated by assessing the suitability of yeast oar1Delta mutant cells lacking mitochondrial 3-oxoacyl-ACP reductase activity to act as a surrogate system for expressing FabG1/MabA directed to the mitochondria. Mutant yeast cells producing this targeted FabG1 variant were essentially wild type for all of the chronicled phenotype characteristics, including respiratory growth on glycerol medium, cytochrome assembly and lipoid acid production. This indicated that within the framework of de novo fatty acid biosynthesis in yeast mitochondria, FabG1 was able to act on shorter (C(4)) acyl substrates than was previously proposed (C(8-20)) during mycolic acid biosynthesis in M. tuberculosis. Thereafter, FabG2-FabG5 were expressed as mitochondrial proteins in the oar1Delta strain, and FabG4 was found to complement the mutant phenotype and contain high levels of 3-oxoacyl-thioester reductase activity. Hence, like FabG1, FabG4 is also an essential, physiologically functional 3-oxoacyl-thioester reductase, albeit the latter's involvement in mycobacterial FASII remains to be explored.

Show MeSH
Related in: MedlinePlus