Studies on the metabolism of unsaturated fatty acids. VIII. Induction of 2,4-dienoyl-CoA reductase in Escherichia coli on the addition of unsaturated fatty acids

Molecular basis of human body odour formation: insights deduced from corynebacterial genome sequences

During the past few decades, there has been an increased interest in the essential role of commensal skin bacteria in human body odour formation. It is now generally accepted that skin bacteria cause body odour by biotransformation of sweat components secreted in the human axillae. Especially, aerobic corynebacteria have been shown to contribute strongly to axillary malodour, whereas other human skin residents seem to have little influence. Analysis of odoriferous sweat components has shown that the major odour-causing substances in human sweat include steroid derivatives, short volatile branched-chain fatty acids and sulphanylalkanols. In this mini-review, we describe the molecular basis of the four most extensively studied routes of human body odour formation, while focusing on the underlying enzymatic processes. Considering the previously reported role of β-oxidation in odour formation, we analysed the genetic repertoire of eight Corynebacterium species concerning fatty acid metabolism. We particularly focused on the metabolic abilities of the lipophilic axillary isolate Corynebacterium jeikeium K411.

Overlapping repressor binding sites result in additive regulation of Escherichia coli FadH by FadR and ArcA

Escherichia coli fadH encodes a 2,4-dienoyl reductase that plays an auxiliary role in beta-oxidation of certain unsaturated fatty acids. In the 2 decades since its discovery, FadH biochemistry has been studied extensively. However, the genetic regulation of FadH has been explored only partially. Here we report mapping of the fadH promoter and document its complex regulation by three independent regulators, the fatty acid degradation FadR repressor, the oxygen-responsive ArcA-ArcB two-component system, and the cyclic AMP receptor protein-cyclic AMP (CRP-cAMP) complex. Electrophoretic mobility shift assays demonstrated that FadR binds to the fadH promoter region and that this binding can be specifically reversed by long-chain acyl-coenzyme A (CoA) thioesters. In vivo data combining transcriptional lacZ fusion and real-time quantitative PCR (qPCR) analyses indicated that fadH is strongly repressed by FadR, in agreement with induction of fadH by long-chain fatty acids. Inactivation of arcA increased fadH transcription by >3-fold under anaerobic conditions. Moreover, fadH expression was increased 8- to 10-fold under anaerobic conditions upon deletion of both the fadR and the arcA gene, indicating that anaerobic expression is additively repressed by FadR and ArcA-ArcB. Unlike fadM, a newly reported member of the E. coli fad regulon that encodes another auxiliary beta-oxidation enzyme, fadH was activated by the CRP-cAMP complex in a manner similar to those of the prototypical fad genes. In the absence of the CRP-cAMP complex, repression of fadH expression by both FadR and ArcA-ArcB was very weak, suggesting a possible interplay with other DNA binding proteins.

The crystal structure and reaction mechanism of Escherichia coli 2,4-dienoyl-CoA reductase

Escherichia coli 2,4-dienoyl-CoA reductase is an iron-sulfur flavoenzyme required for the metabolism of unsaturated fatty acids with double bonds at even carbon positions. The enzyme contains FMN, FAD, and a 4Fe-4S cluster and exhibits sequence homology to another iron-sulfur flavoprotein, trimethylamine dehydrogenase. It also requires NADPH as an electron source, resulting in reduction of the C4-C5 double bond of the acyl chain of the CoA thioester substrate. The structure presented here of a ternary complex of E. coli 2,4-dienoyl-CoA reductase with NADP+ and a fatty acyl-CoA substrate reveals a possible mechanism for substrate reduction and provides details of a plausible electron transfer mechanism involving both flavins and the iron-sulfur cluster. The reaction is initiated by hydride transfer from NADPH to FAD, which in turn transfers electrons, one at a time, to FMN via the 4Fe-4S cluster. In the final stages of the reaction, the fully reduced FMN provides a hydride ion to the C5 atom of substrate, and Tyr-166 and His-252 are proposed to form a catalytic dyad that protonates the C4 atom of the substrate and complete the reaction. Inspection of the substrate binding pocket explains the relative promiscuity of the enzyme, catalyzing reduction of both 2-trans,4-cis- and 2-trans,4-trans-dienoyl-CoA thioesters.

cDNA cloning of rat liver 2,4-dienoyl-CoA reductase

cDNA clones of 2,4-dienoyl-CoA reductase were isolated from rat liver cDNA libraries constructed in phages lambda gt11 and lambda gt10. Hybrid selected translation analysis revealed that 2,4-dienoyl-CoA reductase was translated as a polypeptide with a molecular weight of about 36,000, which was about 3,000 molecular weight units larger than mature reductase. Sequencing analysis revealed that the open reading frame encoded a polypeptide consisting of 335 amino acid residues (predicted molecular weight = 36,132), which contained an N-terminal extension peptide of 34 amino acid residues (presequence) in addition to the mature enzyme. Thus, 2,4-dienoyl-CoA reductase is synthesized as a larger precursor polypeptide, and the N-terminal extension peptide may be acting as the mitochondrial import signal.

3-Hydroxyacyl-CoA epimerase is a peroxisomal enzyme and therefore not involved in mitochondrial fatty acid oxidation

The subcellular location of 3-hydroxyacyl-CoA epimerase (EC 5.1.2.3) was studied by differential centrifugation and Percoll density gradient centrifugation of a rat liver homogenate. The enzyme was found to be associated with peroxisomes but not with mitochondria. This observation proves that 3-hydroxy-acyl-CoA epimerase does not function in mitochondrial beta-oxidation of polyunsaturated fatty acids which are degraded by a modified pathway.

Purification and characterization of 2-enoyl-CoA reductase from bovine liver

Mitochondrial 2-enoyl-CoA reductase from bovine liver was purified and characterized. A simple three-step purification was developed, involving ion-exchange chromatography to separate the bulk of the NADPH-dependent 2,4-dienoyl-CoA reductase, followed by chromatography on Blue Sepharose and adenosine 2',5'-bisphosphate-Sepharose. Homogeneous enzyme with a subunit Mr of 35 500 is obtained in 35% yield. The Mr of the native enzyme, determined by three different methods, yielded values that suggest that the enzyme is dimeric. NADPH is required as cofactor, and cannot be replaced by NADH. The activity of the purified enzyme towards 2-trans-double bonds in 2-monoene and 2,4-diene structures was investigated. 2-Enoyl-CoA reductase reduced the double bonds in a series of 2-trans-monoenoyl-CoA esters with different chain lengths, but did not exhibit significant activity towards 2-trans-double bonds of 2,4-dienoyl-CoA esters. This result is discussed in the light of analogous observations with enoyl-CoA hydratase.