title: MabA (FabG1), a Mycobacterium tuberculosis protein involved in the long-chain fatty acid elongation system FAS-II.
abstract: The fatty acid elongation system FAS-II is involved in the biosynthesis of mycolic acids, which are very long-chain fatty acids of the cell envelope specific to Mycobacterium tuberculosis and other mycobacteria. A potential component of FAS-II, the protein MabA (FabG1), was overexpressed and purified. Sedimentation equilibrium analyses revealed that MabA undergoes a dimer to tetramer self-association with a dissociation constant of 22 microM. The protein was detected by Western blotting in a mycobacterial cell-wall extract that produces mycolic acids and in the FPLC FAS-II fraction. MabA was shown to catalyse the NADPH-specific reduction of beta-ketoacyl derivatives, equivalent to the second step of a FAS-II elongation round. Unlike the known homologous proteins, MabA preferentially metabolizes long-chain substrates (C(8)-C(20)) and has a poor affinity for the C(4) substrate, in agreement with FAS-II specificities. Molecular modelling of MabA structure suggested the presence of an unusually hydrophobic substrate-binding pocket holding a unique Trp residue, suitable for fluorescence spectroscopic analyses. In agreement with the enzyme kinetic data, the spectral properties of MabA were different in the presence of the C(8)-C(16) ligands as compared to the C(4) ligand. Altogether, these data bring out distinctive enzymic and structural properties of MabA, which correlate with its predilection for long-chain substrates, in contrast to most of the other known ketoacyl reductases.
authors.affiliation: Institut de Pharmacologie et de Biologie Structurale, Centre National de la Recherche Scientifique, Université Paul Sabatier (UMR5089), 205 route de Narbonne, 31077 Toulouse cedex, France1.
authors.forename: Hedia
authors.initials: H
authors.lastname: Marrakchi
authors.affiliation: Institut de Pharmacologie et de Biologie Structurale, Centre National de la Recherche Scientifique, Université Paul Sabatier (UMR5089), 205 route de Narbonne, 31077 Toulouse cedex, France1.
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Ducasse
authors.affiliation: Centre de Biochimie Structurale (INSERM U554 - CNRS UMR5048 - UM1), 29 rue de Navacelles, 34090 Montpellier cedex, France2.
authors.forename: Gilles
authors.initials: G
authors.lastname: Labesse
authors.affiliation: Institut de Pharmacologie et de Biologie Structurale, Centre National de la Recherche Scientifique, Université Paul Sabatier (UMR5089), 205 route de Narbonne, 31077 Toulouse cedex, France1.
authors.forename: Henri
authors.initials: H
authors.lastname: Montrozier
authors.affiliation: Centre de Biochimie Structurale (INSERM U554 - CNRS UMR5048 - UM1), 29 rue de Navacelles, 34090 Montpellier cedex, France2.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Margeat
authors.affiliation: Institut de Pharmacologie et de Biologie Structurale, Centre National de la Recherche Scientifique, Université Paul Sabatier (UMR5089), 205 route de Narbonne, 31077 Toulouse cedex, France1.
authors.forename: Laurent
authors.initials: L
authors.lastname: Emorine
authors.affiliation: Institut de Pharmacologie et de Biologie Structurale, Centre National de la Recherche Scientifique, Université Paul Sabatier (UMR5089), 205 route de Narbonne, 31077 Toulouse cedex, France1.
authors.forename: Xavier
authors.initials: X
authors.lastname: Charpentier
authors.affiliation: Institut de Pharmacologie et de Biologie Structurale, Centre National de la Recherche Scientifique, Université Paul Sabatier (UMR5089), 205 route de Narbonne, 31077 Toulouse cedex, France1.
authors.forename: Mamadou
authors.initials: M
authors.lastname: Daffé
authors.affiliation: Institut de Pharmacologie et de Biologie Structurale, Centre National de la Recherche Scientifique, Université Paul Sabatier (UMR5089), 205 route de Narbonne, 31077 Toulouse cedex, France1.
authors.forename: Annaı K
authors.initials: AK
authors.lastname: Quémard
mesh_terms: D064431:3-Oxoacyl-(Acyl-Carrier-Protein) Reductase; D000123:Acetyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000429:Alcohol Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D017931:DNA Primers; D054889:Fatty Acid Synthase, Type II; D064429:Fatty Acid Synthases / Q000235:genetics / Q000378:metabolism; D005230:Fatty Acids, Nonesterified / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009169:Mycobacterium tuberculosis / Q000201:enzymology* / Q000235:genetics; D009171:Mycolic Acids / Q000378:metabolism; D011487:Protein Conformation; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D017931:DNA Primers; D005230:Fatty Acids, Nonesterified; D009097:Multienzyme Complexes; D009171:Mycolic Acids; D000429:Alcohol Oxidoreductases; D064431:3-Oxoacyl-(Acyl-Carrier-Protein) Reductase; D000123:Acetyltransferases; D064429:Fatty Acid Synthases; D054889:Fatty Acid Synthase, Type II; C413881:fatty acid synthase I, mycobacteria