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Biotin synthesis begins by hijacking the fatty acid synthetic pathway.

ABSTRACT: Although biotin is an essential enzyme cofactor found in all three domains of life, our knowledge of its biosynthesis remains fragmentary. Most of the carbon atoms of biotin are derived from pimelic acid, a seven-carbon dicarboxylic acid, but the mechanism whereby this intermediate is assembled remains unknown. Genetic analysis in Escherichia coli identified only two genes of unknown function required for pimelate synthesis, bioC and bioH. We report in vivo and in vitro evidence that the pimeloyl moiety is synthesized by a modified fatty acid synthetic pathway in which the omega-carboxyl group of a malonyl-thioester is methylated by BioC, which allows recognition of this atypical substrate by the fatty acid synthetic enzymes. The malonyl-thioester methyl ester enters fatty acid synthesis as the primer and undergoes two reiterations of the fatty acid elongation cycle to give pimeloyl-acyl carrier protein (ACP) methyl ester, which is hydrolyzed to pimeloyl-ACP and methanol by BioH.

SUBMITTER: Lin S

PROVIDER: S-EPMC2925990 | biostudies-literature | 2010 Sep

REPOSITORIES: biostudies-literature

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Biotin synthesis begins by hijacking the fatty acid synthetic pathway.

Lin Steven S Hanson Ryan E RE Cronan John E JE

Nature chemical biology 20100808 9

Although biotin is an essential enzyme cofactor found in all three domains of life, our knowledge of its biosynthesis remains fragmentary. Most of the carbon atoms of biotin are derived from pimelic acid, a seven-carbon dicarboxylic acid, but the mechanism whereby this intermediate is assembled remains unknown. Genetic analysis in Escherichia coli identified only two genes of unknown function required for pimelate synthesis, bioC and bioH. We report in vivo and in vitro evidence that the pimeloy ...[more]

PMID: 20693992

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Project description:Two vitamins, biotin and lipoic acid, are essential in all three domains of life. Both coenzymes function only when covalently attached to key metabolic enzymes. There they act as "swinging arms" that shuttle intermediates between two active sites (= covalent substrate channeling) of key metabolic enzymes. Although biotin was discovered over 100 years ago and lipoic acid 60 years ago, it was not known how either coenzyme is made until recently. In Escherichia coli the synthetic pathways for both coenzymes have now been worked out for the first time. The late steps of biotin synthesis, those involved in assembling the fused rings, were well described biochemically years ago, although recent progress has been made on the BioB reaction, the last step of the pathway in which the biotin sulfur moiety is inserted. In contrast, the early steps of biotin synthesis, assembly of the fatty acid-like "arm" of biotin were unknown. It has now been demonstrated that the arm is made by using disguised substrates to gain entry into the fatty acid synthesis pathway followed by removal of the disguise when the proper chain length is attained. The BioC methyltransferase is responsible for introducing the disguise, and the BioH esterase is responsible for its removal. In contrast to biotin, which is attached to its cognate proteins as a finished molecule, lipoic acid is assembled on its cognate proteins. An octanoyl moiety is transferred from the octanoyl acyl carrier protein of fatty acid synthesis to a specific lysine residue of a cognate protein by the LipB octanoyltransferase followed by sulfur insertion at carbons C-6 and C-8 by the LipA lipoyl synthetase. Assembly on the cognate proteins regulates the amount of lipoic acid synthesized, and, thus, there is no transcriptional control of the synthetic genes. In contrast, transcriptional control of the biotin synthetic genes is wielded by a remarkably sophisticated, yet simple, system, exerted through BirA, a dual-function protein that both represses biotin operon transcription and ligates biotin to its cognate proteins.

Project description:Methods: We performed mRNA sequence analysis by deep sequencing, in triplicate, using Illumina HiSeq to assess the impact of PHLPP1 knockdown in regulating gene expression in RAW 264.7 cells treated with/without OxLDL. The transcriptome libraries were constructed using the NEB adapters and were sequenced on at 150 nucleotide read length using the paired-end chemistry. The raw reads were subjected to Adapter and low-quality reads removal by Trimmomatic -0.36v. The raw reads were subjected to contamination [structural RNA / low complexity sequences] removal by mapping with bowtie 2-2.2.1. The decontaminated data set was mapped to the mouse genome. Reads mapping to gene list were counted using feature count module of sub reads package. The read counts were normalized in DESeq2-3.5, and subject to differential expression analysis. Differentially expressed genes were selected based on log2-ratio change with p-value <0.05 (Student’s t-test, unpaired). Hierarchical clustering was performed with the programs Cluster (uncentered correlation; average linkage clustering) and Treeview. Results: To gain a deeper understanding of the role of PHLPP1 in lipid metabolism in macrophages, we performed mRNA Seq analysis to assess the gene expression changes in a mouse macrophage cell line. The experiment has been carried out in triplicates. Alignment of the reads showed 97% alignment to the reference mouse genome. Identification of the differentially expressed genes were then carried out by DESeq2 version 1.2.10 with stringent criteria (FDR <0.05% with 2 fold up and down regulation) which reveals in control treated vs. control (121-down, 396-Up), Test vs. Control - (326-down, 569 Up) and Test treated vs. control treated (1314-down, 1328 up) of DEG to be altered in expression respectively. Inference: RNA-seq analysis revealed that PHLPP1 knockdown parallel with OxLDL treatment resulted in diminished expression profile of cholesterol biosynthesis and lipid metabolism genes.

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Biotin synthesis begins by hijacking the fatty acid synthetic pathway.

Publications

Biotin synthesis begins by hijacking the fatty acid synthetic pathway.

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