The essential role of 2,4-dienoyl-CoA reductase for degradation of complex fatty acid mixtures

Abstract

Fatty acids (FAs) can be used as carbon and energy source by most bacteria. FAs are very diverse and show variations in aliphatic chain length, degree and kind of branching, and number of double bonds. After their activation by a thioester link to Coenzyme A, FAs are degraded by the {beta}-oxidation machinery. The core enzymes of the {beta}-oxidation machinery can degrade most FAs, except for those that bear an unsaturation at even-numbered carbons. Such FAs include arachidonic acid or linoleic acid, which are essential FAs of the mammalian diet. We studied the role of the 2,4-dienoyl-CoA reductase FadH in E. coli FA metabolism. We showed that fadH is essential for growth on linoleic acid and that Cys residues connecting FadH-bound [Fe-S] cluster are essential for activity in vivo. Moreover, we showed that when mixed with other FAs, linoleic acid prevents growth of the fadH mutant. These results underline the key role of FadH in complex environments like the gut containing diverse FAs. Eukaryotes also use 2,4-dienoyl-CoA reductases for {beta}-oxidation in mitochondria, but these enzymes belong to a different family than FadH, with different co-factors equipment and mechanism. Yet, we showed that eukaryotic 2,4-dienoyl-CoA reductases DECR can complement the E. coli fadH mutant for growth on linoleic acid and for relief of linoleate mediated jamming of the {beta}-oxidation, paving the way to search for chemicals targeting DECR activity. Altogether these studies demonstrate the key role of prokaryotic and eukaryotic 2,4-dienoyl-CoA reductases in complex environments containing mixtures of saturated and unsaturated FAs. IMPORTANCEBacteria and eukaryotes can harness energy from fatty acids (FAs) through the process of {beta}-oxidation. However, information on the {beta}-oxidation in bacteria stems from studies in which degradation of only a limited set of saturated or monounsaturated FAs were investigated, far from reflecting the wide chemical diversity of FAs found in Nature. Here we evidenced the physiological importance of dienoyl-CoA reductase enzymes required for the degradation of specific unsaturated fatty acids in complex mixtures of fatty acids, and how their absence leads to the congestion of the {beta}-oxidation machinery. These results will permit to better understand the impact of FA degradation in enterobacteria, living in the complex gut environment where FAs are available from the diet or from host lipids. Furthermore, we showed that eukaryotic enzymes can replace the prokaryotic ones, opening the possibility of biomedical application in structure/function studies of the eukaryotic dienoyl-CoA reductases.