An organic O donor for biological hydroxylation reactions.

All biological hydroxylation reactions are thought to derive the oxygen atom from one of three inorganic oxygen donors, O2, H2O2, or H2O. Here, we have identified the organic compound prephenate as the oxygen donor for the three hydroxylation steps of the O2-independent biosynthetic pathway of ubiquinone, a widely distributed lipid coenzyme. Prephenate is an intermediate in the aromatic amino acid pathway and genetic experiments showed that it is essential for ubiquinone biosynthesis in Escherichia coli under anaerobic conditions. Metabolic labeling experiments with 18O-shikimate, a precursor of prephenate, demonstrated the incorporation of 18O atoms into ubiquinone. The role of specific iron-sulfur enzymes belonging to the widespread U32 protein family is discussed. Prephenate-dependent hydroxylation reactions represent a unique biochemical strategy for adaptation to anaerobic environments.

Rational Engineering of Non-Ubiquinone Containing Corynebacterium glutamicum for Enhanced Coenzyme Q10 Production.

Coenzyme Q10 (CoQ10) is a lipid-soluble compound with important physiological functions and is sought after in the food and cosmetic industries owing to its antioxidant properties. In our previous proof of concept, we engineered for CoQ10 biosynthesis the industrially relevant Corynebacterium glutamicum, which does not naturally synthesize any CoQ. Here, liquid chromatography-mass spectrometry (LC-MS) analysis identified two metabolic bottlenecks in the CoQ10 production, i.e., low conversion of the intermediate 10-prenylphenol (10P-Ph) to CoQ10 and the accumulation of isoprenologs with prenyl chain lengths of not only 10, but also 8 to 11 isopentenyl units. To overcome these limitations, the strain was engineered for expression of the Ubi complex accessory factors UbiJ and UbiK from Escherichia coli to increase flux towards CoQ10, and by replacement of the native polyprenyl diphosphate synthase IspB with a decaprenyl diphosphate synthase (DdsA) to select for prenyl chains with 10 isopentenyl units. The best strain UBI6-Rs showed a seven-fold increased CoQ10 content and eight-fold increased CoQ10 titer compared to the initial strain UBI4-Pd, while the abundance of CoQ8, CoQ9, and CoQ11 was significantly reduced. This study demonstrates the application of the recent insight into CoQ biosynthesis to improve metabolic engineering of a heterologous CoQ10 production strain.

The controversy on the ancestral arsenite oxidizing enzyme; deducing evolutionary histories with phylogeny and thermodynamics.

The three presently known enzymes responsible for arsenic-using bioenergetic processes are arsenite oxidase (Aio), arsenate reductase (Arr) and alternative arsenite oxidase (Arx), all of which are molybdoenzymes from the vast group referred to as the Mo/W-bisPGD enzyme superfamily. Since arsenite is present in substantial amounts in hydrothermal environments, frequently considered as vestiges of primordial biochemistry, arsenite-based bioenergetics has long been predicted to be ancient. Conflicting scenarios, however, have been put forward proposing either Arr/Arx or Aio as operating in the ancestral metabolism. Phylogenetic data argue in favor of Aio whereas biochemical and physiological data led several authors to propose Arx/Arr as the most ancient anaerobic arsenite metabolizing enzymes. Here we combine phylogenetic approaches with physiological and biochemical experiments to demonstrate that the Arx/Arr enzymes could not have been functional in the Archaean geological eon. We propose that Arr reacts with menaquinones to reduce arsenate whereas Arx reacts with ubiquinone to oxidize arsenite, in line with thermodynamic considerations. The distribution of the quinone biosynthesis pathways, however, clearly indicates that the ubiquinone pathway is recent. An updated phylogeny of Arx furthermore reinforces the hypothesis of a recent emergence of this enzyme. We therefore conclude that anaerobic arsenite redox conversion in the Archaean must have been performed in a metabolism involving Aio.