The Escherichia coli fadK (ydiD) gene encodes an anerobically regulated short chain acyl-CoA synthetase

We recently reported a new metabolic competency for Escherichia coli, the ability to degrade and utilize fatty acids of various chain lengths as sole carbon and energy sources. This beta-oxidation pathway is distinct from the previously described aerobic fatty acid degradation pathway and requires enzymes encoded by two operons, yfcYX and ydiQRSTD. The yfcYX operon (renamed fadIJ) encodes enzymes required for hydration, oxidation, and thiolytic cleavage of the acyl chain. The ydiQRSTD operon encodes a putative acyl-CoA synthetase, ydiD (renamed fadK), as well as putative electron transport chain components. We report that FadK is as an acyl-CoA synthetase that has a preference for short chain length fatty acid substrates (<10 C atoms). The enzymatic mechanism of FadK is similar to other acyl-CoA synthetases in that it forms an acyl-AMP intermediate prior to the formation of the final acyl-CoA product. Expression of FadK is repressed during aerobic growth and is maximally expressed under anaerobic conditions in the presence of the terminal electron acceptor, fumarate.     

The Burkholderia cenocepacia BDSF quorum sensing fatty acid is synthesized by a bifunctional crotonase homologue having both dehydratase and thioesterase activities

Signal molecules of the diffusible signal factor (DSF) family have been shown recently to be involved in regulation of pathogenesis and biofilm formation in diverse Gram-negative bacteria. DSF signals are reported to be active not only on their cognate bacteria, but also on unrelated bacteria and the pathogenic yeast, Candida albicans. DSFs are monounsaturated fatty acids of medium chain length containing an unusual cis-2 double bond. Although genetic analyses had identified genes involved in DSF synthesis, the pathway of DSF synthesis was unknown. The DSF of the important human pathogen Burkholderia cenocepacia (called BDSF) is cis-2-dodecenoic acid. We report that BDSF is synthesized from a fatty acid synthetic intermediate, the acyl carrier protein (ACP) thioester of 3-hydroxydodecanoic acid. This intermediate is intercepted by protein Bcam0581 and converted to cis-2-dodecenoyl-ACP. Bcam0581 is annotated as a homologue of crotonase, the first enzyme of the fatty acid degradation pathway. We demonstrated Bcam0581to be a bifunctional protein that not only catalysed dehydration of 3-hydroxydodecanoyl-ACP to cis-2-dodecenoyl-ACP, but also cleaved the thioester bond to give the free acid. Both activities required the same set of active-site residues. Although dehydratase and thioesterase activities are known activities of the crotonase superfamily, Bcam0581 is the first protein shown to have both activities.     

Expression of the biotin biosynthetic operon of Escherichia coli is regulated by the rate of protein biotination

In Escherichia coli biotin biosynthesis is repressed by high concentrations of exogenous biotin. This paper reports that upon high level production of the apo form of a biotinated protein, biotin operon expression was derepressed by 8-10-fold. The biotinated protein studied was the 1.3 S subunit of Propionibacterium shermanii, and transcarboxylase derepression was assayed by beta-galactosidase production in strains which carry a lacZ gene altered such that it is transcribed from biotin operon promoters. Depression of beta-galactosidase synthesis upon production of the apo 1.3 S protein was observed over a several hundred-fold range of biotin concentrations and also resulted in an increased level of biotin operon expression at maximally repressing biotin concentrations. Biotin operon derepression by apobiotin protein production seems a direct consequence of the properties of the biotin repressor protein which also functions as the ligase catalyzing the covalent attachment of biotin to apoproteins.     

Isolation and characterization of Saccharomyces cerevisiae mutants defective in glycerol catabolism.

Mutants of the yeast Saccharomyces cerevisiae that are defective in the catabolism of glycerol were isolated, and two types of mutants were obtained. One type was deficient in glycerol kinase activity, whereas the other type was deficient in sn-glycerol 3-phosphate dehydrogenase activity. Genetic analysis indicated that each mutant strain owed its phenotype to a single nuclear mutation, and that the two mutations were complementary. The mutations were not linked to each other or to any of 10 loci tested. In addition, neither mutation was centromere linked. Possible mechanisms for the regulation of these enzymes were tested by growing the parental strain in the presence of various carbon sources.     

Mechanism of the apparent regulation of Escherichia coli unsaturated fatty acid synthesis by exogenous oleic acid.

Starvation of strains of Escherichia coli which are glycerol auxotrophs and are also defective in beta oxidation results in the accumulation of large amounts of free fatty acid (Cronan, J. E., Jr., Weisberg, L. W., and Allen, R. G. (1975) J. Biol. Chem. 250, 5835-5840). We now report that addition of exogenous oleic acid to these cultures results in no decrease in the synthesis of the unsaturated acids of the free fatty acid fraction although a 40 to 60% decrease of [14C]acetate incorporation into phospholipid unsaturated acyl moieties occurs under these conditions. This result indicates that the decreased synthesis of phospholipid unsaturated acyl moieties observed by others during oleic acid supplementation can be attributed to competition between exogenous and endogenously synthesized unsaturated fatty acids rather than a curtailment of unsaturated fatty acid synthesis per se.     

The apparent coupling between synthesis and posttranslational modification of Escherichia coli acyl carrier protein is due to inhibition of amino acid biosynthesis.

Acyl carrier protein (ACP) is modified on serine 36 by the covalent posttranslational attachment of 4'-phosphopantetheine from coenzyme A (CoA), and this modification is required for lipid biosynthesis. Jackowski and Rock (J. Biol. Chem 258:15186-15191, 1983) reported that upon depletion of the CoA pool by starvation for a CoA precursor, no accumulation of the unmodified form of ACP (apo-ACP) was detected. We report that this lack of apo-ACP accumulation results from decreased translation of the acpP mRNAs because of the limitation of the synthesis of glutamate and other amino acids made directly from tricarboxylic acid cycle intermediates.