para-Aminobenzoic Acid Is a Precursor in Coenzyme Q6 Biosynthesis in Saccharomyces cerevisiae

Abstract

Coenzyme Q (ubiquinone or Q) is a crucial mitochondrial lipid required for respiratory electron transport in eukaryotes. 4-Hydroxybenozoate (4HB) is an aromatic ring precursor that forms the benzoquinone ring of Q and is used extensively to examine Q biosynthesis. However, the direct precursor compounds and enzymatic steps for synthesis of 4HB in yeast are unknown. Here we show that para-aminobenzoic acid (pABA), a well known precursor of folate, also functions as a precursor for Q biosynthesis. We suggest a mechanism where Schiff base-mediated deimination forms DMQ 6 quinone, thereby eliminating the nitrogen contributed by pABA. This scheme results in the convergence of the 4HB and pABA pathways in eukaryotic Q biosynthesis and has implications regarding the action of pABAbased antifolates. Coenzyme Q (Q)2 is an essential polyprenylated benzoquinone lipid in cellular energy metabolism. The prenyl tail anchors Q in cellular membranes, whereas the redox chemistry of the benzoquinone ring plays a crucial role in respiratory electron transport, in catabolic and biosynthetic metabolism (1), as a co-antioxidant able to recycle vitamin E, and as a chain-terminating antioxidant (2). In these reactions the quinone ring of Q thus cycles between oxidized and reduced (QH 2 , or hydroquinone) states.Cells rely on de novo synthesis for an adequate supply of Q. Studies in Escherichia coli, Schizosaccharomyces pombe, and Saccharomyces cerevisiae have made use of Q-deficient mutants to elucidate the biosynthetic pathway (3-5). In S. cerevisiae, nine COQ genes are required, and each of the yeast coq mutants (coq1 through coq9) lack Q 6 and are unable to grow on media containing non-fermentable carbon sources such as glycerol or ethanol. The dedicated precursors in the biosynthesis of Q are polyisoprene diphosphate, which provides the tail (S. cerevisiae synthesizes Q 6 , with a tail containing six isoprene units), and 4-hydroxybenzoic acid (4HB) (6, 7). Studies in animal cells and in E. coli indicate that different metabolic pathways are used to produce 4HB. Animals (e.g. rats and humans) generate 4HB from the essential dietary amino acid tyrosine (6 -8). Phenylalanine also acts as a precursor for 4HB, however, the incorporation is thought to proceed primarily following its conversion to tyrosine via phenylalanine hydroxylase (8). The biosynthetic steps leading from 4-hydroxyphenylpyruvate to 4HB in animal cells are not yet characterized (see Fig. 1). E. coli relies on shikimate biosynthesis, the formation of chorismate, and chorismate pyruvate lyase (encoded by the ubiC gene) to synthesize 4HB (9, 10). E. coli ubiC mutants lack Q unless 4HB is provided in the growth media (9). E. coli mutants lacking shikimate or chorismate also require exogenous 4HB to synthesize Q (11). Thus, E. coli cells are unable to convert tyrosine or phenylalanine to Q and rely exclusively on the de novo synthesis of 4HB from chorismate.In contrast, S. cerevisiae may utilize either shikimate or tyrosine to synthesize the aromatic ring precursor of Q (6,...

Identification of Coq11, a New Coenzyme Q Biosynthetic Protein in the CoQ-Synthome in Saccharomyces cerevisiae

“…Analysis of Q 6 and Q 6 Intermediates-Lipid extraction of eluate samples and cells grown in DOD-complete was performed with methanol/petroleum ether and Q 4 as an internal standard, and LC-MS/MS analysis of extracts was performed as described (33). Briefly, a 4000 QTRAP linear MS/MS spectrometer (Applied Biosystems, Foster City, CA) was used, and Analyst version 1.4.2 software (Applied Biosystems) was used for data acquisition and processing.…”

“…Synthetic dextrose/minimal medium was prepared as described (32) and consisted of all components (SDcomplete) or all components minus histidine (SDϪHis). Drop out dextrose medium (DOD) was prepared as described (33), except that galactose was replaced with 2% dextrose. Plate medium was prepared with 2% bacto agar.…”

Resveratrol and para-coumarate serve as ring precursors for coenzyme Q biosynthesis

“…UbiB, an atypical protein kinase similar animal cells (15)(16)(17). Yeast can also use para -aminobenzoic acid (pABA) as an alternate ring precursor in the biosynthesis of Q ( 9,18 ). This fi nding was surprising because pABA is a well-known precursor of folate, which is synthesized de novo by many microorganisms and folate is a vitamin for humans.…”

Engineering yeast shikimate pathway towards production of aromatics: rational design of a chassis cell using systems and synthetic biology

“…The reaction is catalysed by chorismate pyruvate-lyase which is encoded by the gene ubiC (Nichols & Green, 1992). It is remarkable that pHBA can also be detected in yeast though no chorismate lyase analogue has been described to date (Marbois et al, 2010, Pierrel et al, 2010, indicating that either the responsible enzyme has yet to be discovered, or the compound is obtained from a different precursor. It has been proposed that this precursor is rather 4-hydroxyphenylpyruvate then catechol, giving rise to a second pathway to ubiquinone synthesis in yeast (Marbois et al, 2010).…”

“…The shikimate pathway also leads to folate and ubiquinone (coenzyme Q) synthesis via the precursor pABA (Marbois et al, 2010). Outgoing from chorismate, pABA is synthesised in two subsequent reactions catalysed by aminodeoxychorismate synthase and aminodeoxychorismate lyase, the respective yeast genes are ABZ1 and ABZ2.…”