Identification of Coq11, a new coenzyme Q biosynthetic protein in the CoQ-synthome in Saccharomyces cerevisiae

In defence of ferroptosis

Rampant phospholipid peroxidation initiated by iron causes ferroptosis unless this is restrained by cellular defences. Ferroptosis is increasingly implicated in a host of diseases, and unlike other cell death programs the physiological initiation of ferroptosis is conceived to occur not by an endogenous executioner, but by the withdrawal of cellular guardians that otherwise constantly oppose ferroptosis induction. Here, we profile key ferroptotic defence strategies including iron regulation, phospholipid modulation and enzymes and metabolite systems: glutathione reductase (GR), Ferroptosis suppressor protein 1 (FSP1), NAD(P)H Quinone Dehydrogenase 1 (NQO1), Dihydrofolate reductase (DHFR), retinal reductases and retinal dehydrogenases (RDH) and thioredoxin reductases (TR). A common thread uniting all key enzymes and metabolites that combat lipid peroxidation during ferroptosis is a dependence on a key cellular reductant, nicotinamide adenine dinucleotide phosphate (NADPH). We will outline how cells control central carbon metabolism to produce NADPH and necessary precursors to defend against ferroptosis. Subsequently we will discuss evidence for ferroptosis and NADPH dysregulation in different disease contexts including glucose-6-phosphate dehydrogenase deficiency, cancer and neurodegeneration. Finally, we discuss several anti-ferroptosis therapeutic strategies spanning the use of radical trapping agents, iron modulation and glutathione dependent redox support and highlight the current landscape of clinical trials focusing on ferroptosis.

Mitochondrial-ER Contact Sites and Tethers Influence the Biosynthesis and Function of Coenzyme Q

Coenzyme Q (CoQ) is an essential redox-active lipid that plays a major role in the electron transport chain, driving mitochondrial ATP synthesis. In Saccharomyces cerevisiae (yeast), CoQ biosynthesis occurs exclusively in the mitochondrial matrix via a large protein-lipid complex, the CoQ synthome, comprised of CoQ itself, late-stage CoQ-intermediates, and the polypeptides Coq3-Coq9 and Coq11. Coq11 is suggested to act as a negative modulator of CoQ synthome assembly and CoQ synthesis, as its deletion enhances Coq polypeptide content, produces an enlarged CoQ synthome, and restores respiration in mutants lacking the CoQ chaperone polypeptide, Coq10. The CoQ synthome resides in specific niches within the inner mitochondrial membrane, termed CoQ domains, that are often located adjacent to the endoplasmic reticulum-mitochondria encounter structure (ERMES). Loss of ERMES destabilizes the CoQ synthome and renders CoQ biosynthesis less efficient. Here we show that deletion of COQ11 suppresses the respiratory deficient phenotype of select ERMES mutants, results in repair and reorganization of the CoQ synthome, and enhances mitochondrial CoQ domains. Given that ER-mitochondrial contact sites coordinate CoQ biosynthesis, we used a Split-MAM (Mitochondrial Associated Membrane) artificial tether consisting of an ER-mitochondrial contact site reporter, to evaluate the effects of artificial membrane tethers on CoQ biosynthesis in both wild-type and ERMES mutant yeast strains. Overall, this work identifies the deletion of COQ11 as a novel suppressor of phenotypes associated with ERMES deletion mutants and indicates that ER-mitochondria tethers influence CoQ content and turnover, highlighting the role of membrane contact sites in regulating mitochondrial respiratory homeostasis.

Nonfunctional coq10 mutants maintain the ERMES complex and reveal true phenotypes associated with the loss of the coenzyme Q chaperone protein Coq10

Coenzyme Q (CoQ) is a redox-active lipid molecule that acts as an electron carrier in the mitochondrial electron transport chain. In Saccharomyces cerevisiae, CoQ is synthesized in the mitochondrial matrix by a multisubunit protein-lipid complex termed the CoQ synthome, the spatial positioning of which is coordinated by the endoplasmic reticulum-mitochondria encounter structure (ERMES). The MDM12 gene encoding the cytosolic subunit of ERMES is coexpressed with COQ10, which encodes the putative CoQ chaperone Coq10, via a shared bidirectional promoter. Deletion of COQ10 results in respiratory deficiency, impaired CoQ biosynthesis, and reduced spatial coordination between ERMES and the CoQ synthome. While Coq10 protein content is maintained upon deletion of MDM12, we show that deletion of COQ10 by replacement with a HIS3 marker results in diminished Mdm12 protein content. Since deletion of individual ERMES subunits prevents ERMES formation, we asked whether some or all of the phenotypes associated with COQ10 deletion result from ERMES dysfunction. To identify the phenotypes resulting solely due to the loss of Coq10, we constructed strains expressing a functionally impaired (coq10-L96S) or truncated (coq10-R147∗) Coq10 isoform using CRISPR-Cas9. We show that both coq10 mutants preserve Mdm12 protein content and exhibit impaired respiratory capacity like the coq10Δ mutant, indicating that Coq10's function is vital for respiration regardless of ERMES integrity. Moreover, the maintenance of CoQ synthome stability and efficient CoQ biosynthesis observed for the coq10-R147∗ mutant suggests these deleterious phenotypes in the coq10Δ mutant result from ERMES disruption. Overall, this study clarifies the role of Coq10 in modulating CoQ biosynthesis.

Understanding coenzyme Q

Coenzyme Q (CoQ), also known as ubiquinone, comprises a benzoquinone head group and a long isoprenoid side chain. It is thus extremely hydrophobic and resides in membranes. It is best known for its complex function as an electron transporter in the mitochondrial electron transport chain (ETC) but is also required for several other crucial cellular processes. In fact, CoQ appears to be central to the entire redox balance of the cell. Remarkably, its structure and therefore its properties have not changed from bacteria to vertebrates. In metazoans, it is synthesized in all cells and is found in most, and maybe all, biological membranes. CoQ is also known as a nutritional supplement, mostly because of its involvement with antioxidant defenses. However, whether there is any health benefit from oral consumption of CoQ is not well established. Here we review the function of CoQ as a redox-active molecule in the ETC and other enzymatic systems, its role as a prooxidant in reactive oxygen species generation, and its separate involvement in antioxidant mechanisms. We also review CoQ biosynthesis, which is particularly complex because of its extreme hydrophobicity, as well as the biological consequences of primary and secondary CoQ deficiency, including in human patients. Primary CoQ deficiency is a rare inborn condition due to mutation in CoQ biosynthetic genes. Secondary CoQ deficiency is much more common, as it accompanies a variety of pathological conditions, including mitochondrial disorders as well as aging. In this context, we discuss the importance, but also the great difficulty, of alleviating CoQ deficiency by CoQ supplementation.

Hem25p is required for mitochondrial IPP transport in fungi

Coenzyme Q (CoQ, ubiquinone) is an essential cellular cofactor composed of a redox-active quinone head group and a long hydrophobic polyisoprene tail. How mitochondria access cytosolic isoprenoids for CoQ biosynthesis is a longstanding mystery. Here, via a combination of genetic screening, metabolic tracing and targeted uptake assays, we reveal that Hem25p-a mitochondrial glycine transporter required for haem biosynthesis-doubles as an isopentenyl pyrophosphate (IPP) transporter in Saccharomyces cerevisiae. Mitochondria lacking Hem25p failed to efficiently incorporate IPP into early CoQ precursors, leading to loss of CoQ and turnover of CoQ biosynthetic proteins. Expression of Hem25p in Escherichia coli enabled robust IPP uptake and incorporation into the CoQ biosynthetic pathway. HEM25 orthologues from diverse fungi, but not from metazoans, were able to rescue hem25∆ CoQ deficiency. Collectively, our work reveals that Hem25p drives the bulk of mitochondrial isoprenoid transport for CoQ biosynthesis in fungi.

Primary Coenzyme Q10 Deficiency: An Update

Coenzyme Q10 (CoQ10) has a number of vital functions in all cells, both mitochondrial and extra-mitochondrial. In addition to its key role in mitochondrial oxidative phosphorylation, CoQ10 serves as a lipid soluble antioxidant and plays an important role in fatty acid beta-oxidation and pyrimidine and lysosomal metabolism, as well as directly mediating the expression of a number of genes, including those involved in inflammation. Due to the multiplicity of roles in cell function, it is not surprising that a deficiency in CoQ10 has been implicated in the pathogenesis of a wide range of disorders. CoQ10 deficiency is broadly divided into primary and secondary types. Primary CoQ10 deficiency results from mutations in genes involved in the CoQ10 biosynthetic pathway. In man, at least 10 genes are required for the biosynthesis of functional CoQ10, a mutation in any one of which can result in a deficit in CoQ10 status. Patients may respond well to oral CoQ10 supplementation, although the condition must be recognised sufficiently early, before irreversible tissue damage has occurred. In this article, we have reviewed clinical studies (up to March 2023) relating to the identification of these deficiencies, and the therapeutic outcomes of CoQ10 supplementation; we have attempted to resolve the disparities between previous review articles regarding the usefulness or otherwise of CoQ10 supplementation in these disorders. In addition, we have highlighted several of the potential problems relating to CoQ10 supplementation in primary CoQ10 deficiency, as well as identifying unresolved issues relating to these disorders that require further research.

Biosynthesis, Deficiency, and Supplementation of Coenzyme Q

Originally identified as a key component of the mitochondrial respiratory chain, Coenzyme Q (CoQ or CoQ₁₀ for human tissues) has recently been revealed to be essential for many different redox processes, not only in the mitochondria, but elsewhere within other cellular membrane types. Cells rely on endogenous CoQ biosynthesis, and defects in this still-not-completely understood pathway result in primary CoQ deficiencies, a group of conditions biochemically characterised by decreased tissue CoQ levels, which in turn are linked to functional defects. Secondary CoQ deficiencies may result from a wide variety of cellular dysfunctions not directly linked to primary synthesis. In this article, we review the current knowledge on CoQ biosynthesis, the defects leading to diminished CoQ₁₀ levels in human tissues and their associated clinical manifestations.

Identification of novel coenzyme Q10 biosynthetic proteins Coq11 and Coq12 in Schizosaccharomyces pombe

Coenzyme Q (CoQ) is an essential component of the electron transport system in aerobic organisms. CoQ10 has ten isoprene units in its quinone structure and is especially valuable as a food supplement. However, the CoQ biosynthetic pathway has not been fully elucidated, including synthesis of the p-hydroxybenzoic acid (PHB) precursor to form a quinone backbone. To identify the novel components of CoQ10 synthesis, we investigated CoQ10 production in 400 Schizosaccharomyces pombe gene-deleted strains in which individual mitochondrial proteins were lost. We found that deletion of coq11 (an S. cerevisiae COQ11 homolog) and a novel gene designated coq12 lowered CoQ levels to ∼4% of that of the WT strain. Addition of PHB or p-hydroxybenzaldehyde restored the CoQ content and growth and lowered hydrogen sulfide production of the Δcoq12 strain, but these compounds did not affect the Δcoq11 strain. The primary structure of Coq12 has a flavin reductase motif coupled with an NAD+ reductase domain. We determined that purified Coq12 protein from S. pombe displayed NAD+ reductase activity when incubated with ethanol-extracted substrate of S. pombe. Because purified Coq12 from Escherichia coli did not exhibit reductase activity under the same conditions, an extra protein is thought to be necessary for its activity. Analysis of Coq12-interacting proteins by LC-MS/MS revealed interactions with other Coq proteins, suggesting formation of a complex. Thus, our analysis indicates that Coq12 is required for PHB synthesis, and it has diverged among species.

Coenzyme Q biochemistry and biosynthesis

Coenzyme Q (CoQ) is a remarkably hydrophobic, redox-active lipid that empowers diverse cellular processes. Although most known for shuttling electrons between mitochondrial electron transport chain (ETC) complexes, the roles for CoQ are far more wide-reaching and ever-expanding. CoQ serves as a conduit for electrons from myriad pathways to enter the ETC, acts as a cofactor for biosynthetic and catabolic reactions, detoxifies damaging lipid species, and engages in cellular signaling and oxygen sensing. Many open questions remain regarding the biosynthesis, transport, and metabolism of CoQ, which hinders our ability to treat human CoQ deficiency. Here, we recount progress in filling these knowledge gaps, highlight unanswered questions, and underscore the need for novel tools to enable discoveries and improve the treatment of CoQ-related diseases.

Hem25p is a mitochondrial IPP transporter

Coenzyme Q (CoQ, ubiquinone) is an essential cellular cofactor comprised of a redox-active quinone head group and a long hydrophobic polyisoprene tail. How mitochondria access cytosolic isoprenoids for CoQ biosynthesis is a longstanding mystery. Here, via a combination of genetic screening, metabolic tracing, and targeted uptake assays, we reveal that Hem25p-a mitochondrial glycine transporter required for heme biosynthesis-doubles as an isopentenyl pyrophosphate (IPP) transporter in Saccharomyces cerevisiae. Mitochondria lacking Hem25p fail to efficiently incorporate IPP into early CoQ precursors, leading to loss of CoQ and turnover of CoQ biosynthetic proteins. Expression of Hem25p in Escherichia coli enables robust IPP uptake demonstrating that Hem25p is sufficient for IPP transport. Collectively, our work reveals that Hem25p drives the bulk of mitochondrial isoprenoid transport for CoQ biosynthesis in yeast.

Predicting and Understanding the Pathology of Single Nucleotide Variants in Human COQ Genes

Coenzyme Q (CoQ) is a vital lipid that functions as an electron carrier in the mitochondrial electron transport chain and as a membrane-soluble antioxidant. Deficiencies in CoQ lead to metabolic diseases with a wide range of clinical manifestations. There are currently few treatments that can slow or stop disease progression. Primary CoQ₁₀ deficiency can arise from mutations in any of the COQ genes responsible for CoQ biosynthesis. While many mutations in these genes have been identified, the clinical significance of most of them remains unclear. Here we analyzed the structural and functional impact of 429 human missense single nucleotide variants (SNVs) that give rise to amino acid substitutions in the conserved and functional regions of human genes encoding a high molecular weight complex known as the CoQ synthome (or Complex Q), consisting of the COQ3-COQ7 and COQ9 gene products. Using structures of COQ polypeptides, close homologs, and AlphaFold models, we identified 115 SNVs that are potentially pathogenic. Further biochemical characterizations in model organisms such as Saccharomyces cerevisiae are required to validate the pathogenicity of the identified SNVs. Collectively, our results will provide a resource for clinicians during patient diagnosis and guide therapeutic efforts toward combating primary CoQ₁₀ deficiency.

Structure and functionality of a multimeric human COQ7:COQ9 complex

Coenzyme Q (CoQ) is a redox-active lipid essential for core metabolic pathways and antioxidant defense. CoQ is synthesized upon the mitochondrial inner membrane by an ill-defined "complex Q" metabolon. Here, we present structure-function analyses of a lipid-, substrate-, and NADH-bound complex comprising two complex Q subunits: the hydroxylase COQ7 and the lipid-binding protein COQ9. We reveal that COQ7 adopts a ferritin-like fold with a hydrophobic channel whose substrate-binding capacity is enhanced by COQ9. Using molecular dynamics, we further show that two COQ7:COQ9 heterodimers form a curved tetramer that deforms the membrane, potentially opening a pathway for the CoQ intermediates to translocate from the bilayer to the proteins' lipid-binding sites. Two such tetramers assemble into a soluble octamer with a pseudo-bilayer of lipids captured within. Together, these observations indicate that COQ7 and COQ9 cooperate to access hydrophobic precursors within the membrane and coordinate subsequent synthesis steps toward producing CoQ.

Chemistry of Lipoquinones: Properties, Synthesis, and Membrane Location of Ubiquinones, Plastoquinones, and Menaquinones

Lipoquinones are the topic of this review and are a class of hydrophobic lipid molecules with key biological functions that are linked to their structure, properties, and location within a biological membrane. Ubiquinones, plastoquinones, and menaquinones vary regarding their quinone headgroup, isoprenoid sidechain, properties, and biological functions, including the shuttling of electrons between membrane-bound protein complexes within the electron transport chain. Lipoquinones are highly hydrophobic molecules that are soluble in organic solvents and insoluble in aqueous solution, causing obstacles in water-based assays that measure their chemical properties, enzyme activities and effects on cell growth. Little is known about the location and ultimately movement of lipoquinones in the membrane, and these properties are topics described in this review. Computational studies are particularly abundant in the recent years in this area, and there is far less experimental evidence to verify the often conflicting interpretations and conclusions that result from computational studies of very different membrane model systems. Some recent experimental studies have described using truncated lipoquinone derivatives, such as ubiquinone-2 (UQ-2) and menaquinone-2 (MK-2), to investigate their conformation, their location in the membrane, and their biological function. Truncated lipoquinone derivatives are soluble in water-based assays, and hence can serve as excellent analogs for study even though they are more mobile in the membrane than the longer chain counterparts. In this review, we will discuss the properties, location in the membrane, and syntheses of three main classes of lipoquinones including truncated derivatives. Our goal is to highlight the importance of bridging the gap between experimental and computational methods and to incorporate properties-focused considerations when proposing future studies relating to the function of lipoquinones in membranes.

How plants synthesize coenzyme Q

Coenzyme Q (CoQ) is a conserved redox-active lipid that has a wide distribution across the domains of life. CoQ plays a key role in the oxidative electron transfer chain and serves as a crucial antioxidant in cellular membranes. Our understanding of CoQ biosynthesis in eukaryotes has come mostly from studies of yeast. Recently, significant advances have been made in understanding CoQ biosynthesis in plants. Unique mitochondrial flavin-dependent monooxygenase and benzenoid ring precursor biosynthetic pathways have been discovered, providing new insights into the diversity of CoQ biosynthetic pathways and the evolution of phototrophic eukaryotes. We summarize research progress on CoQ biosynthesis and regulation in plants and recent efforts to increase the CoQ content in plant foods.

Recent advances in the metabolic pathways and microbial production of coenzyme Q

Coenzyme Q (CoQ) serves as an electron carrier in aerobic respiration and has become an interesting target for biotechnological production due to its antioxidative effect and benefits in supplementation to patients with various diseases. Here, we review discovery of the pathway with a particular focus on its superstructuration and regulation, and we summarize the metabolic engineering strategies for overproduction of CoQ by microorganisms. Studies in model microorganisms elucidated the details of CoQ biosynthesis and revealed the existence of multiprotein complexes composed of several enzymes that catalyze consecutive reactions in the CoQ pathways of Saccharomyces cerevisiae and Escherichia coli. Recent findings indicate that the identity and the total number of proteins involved in CoQ biosynthesis vary between species, which raises interesting questions about the evolution of the pathway and could provide opportunities for easier engineering of CoQ production. For the biotechnological production, so far only microorganisms have been used that naturally synthesize CoQ₁₀ or a related CoQ species. CoQ biosynthesis requires the aromatic precursor 4-hydroxybenzoic acid and the prenyl side chain that defines the CoQ species. Up to now, metabolic engineering strategies concentrated on the overproduction of the prenyl side chain as well as fine-tuning the expression of ubi genes from the ubiquinone modification pathway, resulting in high CoQ yields. With expanding knowledge about CoQ biosynthesis and exploration of new strategies for strain engineering, microbial CoQ production is expected to improve.

A unique flavoenzyme operates in ubiquinone biosynthesis in photosynthesis-related eukaryotes

Coenzyme Q (CoQ) is an electron transporter in the mitochondrial respiratory chain, yet the biosynthetic pathway in eukaryotes remains only partially resolved. C6-hydroxylation completes the benzoquinone ring full substitution, a hallmark of CoQ. Here, we show that plants use a unique flavin-dependent monooxygenase (CoqF), instead of di-iron enzyme (Coq7) operating in animals and fungi, as a C6-hydroxylase. CoqF evolved early in eukaryotes and became widely distributed in photosynthetic and related organisms ranging from plants, algae, apicomplexans, and euglenids. Independent alternative gene losses in different groups and lateral gene transfer have ramified CoqF across the eukaryotic tree with predominance in green lineages. The exclusive presence of CoqF in Streptophyta hints at an association of the flavoenzyme with photoautotrophy in terrestrial environments. CoqF provides a phylogenetic marker distinguishing eukaryotes and represents a previously unknown target for drug design against parasitic protists.

Engineering high coenzyme Q10 tomato

Coenzyme Q (CoQ) is vital for energy metabolism in living organisms. In humans, CoQ₁₀ deficiency causes diseases and must be replenished via diet; however, CoQ content in plant foods is primarily low. Here, we report the breeding of high CoQ₁₀ tomato lines by expressing four enzymes with a fruit-specific promoter, which modifies the chloroplast chorismate pathway, enhances cytosolic isoprenoid biosynthesis, and up-regulates the first two reactions in mitochondrion that construct the CoQ₁₀ polyisoprenoid tail. We show that, while the level of the aromatic precursor could be markedly elevated, head group prenylation is the key to increasing the final CoQ₁₀ yield. In the HUCD lines expressing all four transgenes, the highest CoQ₁₀ content (0.15 mg/g dry weight) shows a seven-fold increase from the wild-type level and reaches an extraordinarily rich CoQ₁₀ food grade. Overviewing the changes in other terpenoids by transcriptome and metabolic analyses reveals variable contents of carotenoids and α-tocopherol in the HUCD lines. In addition to the enigmatic relations among different terpenoid pathways, high CoQ₁₀ plants maintaining substantial levels of either vitamin can be selected. Our investigation paves the way for the development of CoQ₁₀-enriched crops as dietary supplements.

Effects of Iron and Zinc on Mitochondria: Potential Mechanisms of Glaucomatous Injury

Glaucoma is the most substantial cause of irreversible blinding, which is accompanied by progressive retinal ganglion cell damage. Retinal ganglion cells are energy-intensive neurons that connect the brain and retina, and depend on mitochondrial homeostasis to transduce visual information through the brain. As cofactors that regulate many metabolic signals, iron and zinc have attracted increasing attention in studies on neurons and neurodegenerative diseases. Here, we summarize the research connecting iron, zinc, neuronal mitochondria, and glaucomatous injury, with the aim of updating and expanding the current view of how retinal ganglion cells degenerate in glaucoma, which can reveal novel potential targets for neuroprotection.

Coenzyme Q Biosynthesis: An Update on the Origins of the Benzenoid Ring and Discovery of New Ring Precursors

Coenzyme Q (ubiquinone or CoQ) is a conserved polyprenylated lipid essential for mitochondrial respiration. CoQ is composed of a redox-active benzoquinone ring and a long polyisoprenyl tail that serves as a membrane anchor. A classic pathway leading to CoQ biosynthesis employs 4-hydroxybenzoic acid (4HB). Recent studies with stable isotopes in E. coli, yeast, and plant and animal cells have identified CoQ intermediates and new metabolic pathways that produce 4HB. Stable isotope labeling has identified para-aminobenzoic acid as an alternate ring precursor of yeast CoQ biosynthesis, as well as other natural products, such as kaempferol, that provide ring precursors for CoQ biosynthesis in plants and mammals. In this review, we highlight how stable isotopes can be used to delineate the biosynthetic pathways leading to CoQ.

Primary Coenzyme Q deficiencies: A literature review and online platform of clinical features to uncover genotype-phenotype correlations

Primary Coenzyme Q (CoQ) deficiencies are clinically heterogeneous conditions and lack clear genotype-phenotype correlations, complicating diagnosis and prognostic assessment. Here we present a compilation of all the symptoms and patients with primary CoQ deficiency described in the literature so far and analyse the most common clinical manifestations associated with pathogenic variants identified in the different COQ genes. In addition, we identified new associations between the age of onset of symptoms and different pathogenic variants, which could help to a better diagnosis and guided treatment. To make these results useable for clinicians, we created an online platform (https://coenzymeQbiology.github.io/clinic-CoQ-deficiency) about clinical manifestations of primary CoQ deficiency that will be periodically updated to incorporate new information published in the literature. Since CoQ primary deficiency is a rare disease, the available data are still limited, but as new patients are added over time, this tool could become a key resource for a more efficient diagnosis of this pathology.

Mitochondrial ATP-Dependent Proteases-Biological Function and Potential Anti-Cancer Targets

Cells must eliminate excess or damaged proteins to maintain protein homeostasis. To ensure protein homeostasis in the cytoplasm, cells rely on the ubiquitin-proteasome system and autophagy. In the mitochondria, protein homeostasis is regulated by mitochondria proteases, including four core ATP-dependent proteases, m-AAA, i-AAA, LonP, and ClpXP, located in the mitochondrial membrane and matrix. This review will discuss the function of mitochondrial proteases, with a focus on ClpXP as a novel therapeutic target for the treatment of malignancy. ClpXP maintains the integrity of the mitochondrial respiratory chain and regulates metabolism by degrading damaged and misfolded mitochondrial proteins. Inhibiting ClpXP genetically or chemically impairs oxidative phosphorylation and is toxic to malignant cells with high ClpXP expression. Likewise, hyperactivating the protease leads to increased degradation of ClpXP substrates and kills cancer cells. Thus, targeting ClpXP through inhibition or hyperactivation may be novel approaches for patients with malignancy.

Benzoic acid inhibits Coenzyme Q biosynthesis in Schizosaccharomyces pombe

Coenzyme Q (CoQ, ubiquinone) is an essential component of the electron transport system in aerobic organisms. Human type CoQ₁₀, which has 10 units of isoprene in its quinone structure, is especially valuable as a food supplement. Therefore, studying the biosynthesis of CoQ₁₀ is important not only for increasing metabolic knowledge, but also for improving biotechnological production. Herein, we show that Schizosaccharomyces pombe utilizes p-aminobenzoate (PABA) in addition to p-hydroxybenzoate (PHB) as a precursor for CoQ₁₀ synthesis. We explored compounds that affect the synthesis of CoQ₁₀ and found benzoic acid (Bz) at >5 μg/mL inhibited CoQ biosynthesis without accumulation of apparent CoQ intermediates. This inhibition was counteracted by incubation with a 10-fold lower amount of PABA or PHB. Overexpression of PHB-polyprenyl transferase encoded by ppt1 (coq2) also overcame the inhibition of CoQ biosynthesis by Bz. Inhibition by Bz was efficient in S. pombe and Schizosaccharomyces japonicus, but less so in Saccharomyces cerevisiae, Aureobasidium pullulans, and Escherichia coli. Bz also inhibited a S. pombe ppt1 (coq2) deletion strain expressing human COQ2, and this strain also utilized PABA as a precursor of CoQ₁₀. Thus, Bz is likely to inhibit prenylation reactions involving PHB or PABA catalyzed by Coq2.

Human Mitochondrial Pathologies of the Respiratory Chain and ATP Synthase: Contributions from Studies of Saccharomyces cerevisiae

The ease with which the unicellular yeast Saccharomyces cerevisiae can be manipulated genetically and biochemically has established this organism as a good model for the study of human mitochondrial diseases. The combined use of biochemical and molecular genetic tools has been instrumental in elucidating the functions of numerous yeast nuclear gene products with human homologs that affect a large number of metabolic and biological processes, including those housed in mitochondria. These include structural and catalytic subunits of enzymes and protein factors that impinge on the biogenesis of the respiratory chain. This article will review what is currently known about the genetics and clinical phenotypes of mitochondrial diseases of the respiratory chain and ATP synthase, with special emphasis on the contribution of information gained from pet mutants with mutations in nuclear genes that impair mitochondrial respiration. Our intent is to provide the yeast mitochondrial specialist with basic knowledge of human mitochondrial pathologies and the human specialist with information on how genes that directly and indirectly affect respiration were identified and characterized in yeast.

Mitochondrial ClpP serine protease-biological function and emerging target for cancer therapy

Mitochondrial ClpP is a serine protease located in the mitochondrial matrix. This protease participates in mitochondrial protein quality control by degrading misfolded or damaged proteins, thus maintaining normal metabolic function. Mitochondrial ClpP is a stable heptamer ring with peptidase activity that forms a multimeric complex with the ATP-dependent unfoldase ClpX (ClpXP) leading to proteolytic activity. Emerging evidence demonstrates that ClpXP is over-expressed in hematologic malignancies and solid tumors and is necessary for the viability of a subset of tumors. In addition, both inhibition and hyperactivation of ClpXP leads to impaired respiratory chain activity and causes cell death in cancer cells. Therefore, targeting mitochondrial ClpXP could be a novel therapeutic strategy for the treatment of malignancy. Here, we review the structure and function of mitochondrial ClpXP as well as strategies to target this enzyme complex as a novel therapeutic approach for malignancy.

Disorders of Human Coenzyme Q10 Metabolism: An Overview

Coenzyme Q10 (CoQ10) has a number of vital functions in all cells, both mitochondrial and extramitochondrial. In addition to its key role in mitochondrial oxidative phosphorylation, CoQ10 serves as a lipid soluble antioxidant, plays an important role in fatty acid, pyrimidine and lysosomal metabolism, as well as directly mediating the expression of a number of genes, including those involved in inflammation. In view of the central role of CoQ10 in cellular metabolism, it is unsurprising that a CoQ10 deficiency is linked to the pathogenesis of a range of disorders. CoQ10 deficiency is broadly classified into primary or secondary deficiencies. Primary deficiencies result from genetic defects in the multi-step biochemical pathway of CoQ10 synthesis, whereas secondary deficiencies can occur as result of other diseases or certain pharmacotherapies. In this article we have reviewed the clinical consequences of primary and secondary CoQ10 deficiencies, as well as providing some examples of the successful use of CoQ10 supplementation in the treatment of disease.

Intragenic suppressor mutations of the COQ8 protein kinase homolog restore coenzyme Q biosynthesis and function in Saccharomyces cerevisiae

Saccharomyces cerevisiae Coq8 is a member of the ancient UbiB atypical protein kinase family. Coq8, and its orthologs UbiB, ABC1, ADCK3, and ADCK4, are required for the biosynthesis of coenzyme Q in yeast, E. coli, A. thaliana, and humans. Each Coq8 ortholog retains nine highly conserved protein kinase-like motifs, yet its functional role in coenzyme Q biosynthesis remains mysterious. Coq8 may function as an ATPase whose activity is stimulated by coenzyme Q intermediates and phospholipids. A key yeast point mutant expressing Coq8-A197V was previously shown to result in a coenzyme Q-less, respiratory deficient phenotype. The A197V substitution occurs in the crucial Ala-rich protein kinase-like motif I of yeast Coq8. Here we show that long-term cultures of mutants expressing Coq8-A197V produce spontaneous revertants with the ability to grow on medium containing a non-fermentable carbon source. Each revertant is shown to harbor a secondary intragenic suppressor mutation within the COQ8 gene. The intragenic suppressors restore the synthesis of coenzyme Q. One class of the suppressors fully restores the levels of coenzyme Q and key Coq polypeptides necessary for the maintenance and integrity of the high-molecular mass CoQ synthome (also termed complex Q), while the other class provides only a partial rescue. Mutants harboring the first class of suppressors grow robustly under respiratory conditions, while mutants containing the second class grow more slowly under these conditions. Our work provides insight into the function of this important yet still enigmatic Coq8 family.

COQ11 deletion mitigates respiratory deficiency caused by mutations in the gene encoding the coenzyme Q chaperone protein Coq10

Coenzyme Q (Q _n ) is a vital lipid component of the electron transport chain that functions in cellular energy metabolism and as a membrane antioxidant. In the yeast Saccharomyces cerevisiae, coq1-coq9 deletion mutants are respiratory-incompetent, sensitive to lipid peroxidation stress, and unable to synthesize Q₆ The yeast coq10 deletion mutant is also respiratory-deficient and sensitive to lipid peroxidation, yet it continues to produce Q₆ at an impaired rate. Thus, Coq10 is required for the function of Q₆ in respiration and as an antioxidant and is believed to chaperone Q₆ from its site of synthesis to the respiratory complexes. In several fungi, Coq10 is encoded as a fusion polypeptide with Coq11, a recently identified protein of unknown function required for efficient Q₆ biosynthesis. Because "fused" proteins are often involved in similar biochemical pathways, here we examined the putative functional relationship between Coq10 and Coq11 in yeast. We used plate growth and Seahorse assays and LC-MS/MS analysis to show that COQ11 deletion rescues respiratory deficiency, sensitivity to lipid peroxidation, and decreased Q₆ biosynthesis of the coq10Δ mutant. Additionally, immunoblotting indicated that yeast coq11Δ mutants accumulate increased amounts of certain Coq polypeptides and display a stabilized CoQ synthome. These effects suggest that Coq11 modulates Q₆ biosynthesis and that its absence increases mitochondrial Q₆ content in the coq10Δcoq11Δ double mutant. This augmented mitochondrial Q₆ content counteracts the respiratory deficiency and lipid peroxidation sensitivity phenotypes of the coq10Δ mutant. This study further clarifies the intricate connection between Q₆ biosynthesis, trafficking, and function in mitochondrial metabolism.

Mitochondrial Proteases: Multifaceted Regulators of Mitochondrial Plasticity

Mitochondria are essential metabolic hubs that dynamically adapt to physiological demands. More than 40 proteases residing in different compartments of mitochondria, termed mitoproteases, preserve mitochondrial proteostasis and are emerging as central regulators of mitochondrial plasticity. These multifaceted enzymes limit the accumulation of short-lived, regulatory proteins within mitochondria, modulate the activity of mitochondrial proteins by protein processing, and mediate the degradation of damaged proteins. Various signaling cascades coordinate the activity of mitoproteases to preserve mitochondrial homeostasis and ensure cell survival. Loss of mitoproteases severely impairs the functional integrity of mitochondria, is associated with aging, and causes pleiotropic diseases. Understanding the dual function of mitoproteases as regulatory and quality control enzymes will help unravel the role of mitochondrial plasticity in aging and disease.

The Complexity of Making Ubiquinone

Ubiquinone (UQ, coenzyme Q) is an essential electron transfer lipid in the mitochondrial respiratory chain. It is a main source of mitochondrial reactive oxygen species (ROS) but also has antioxidant properties. This mix of characteristics is why ubiquinone supplementation is considered a potential therapy for many diseases involving mitochondrial dysfunction. Mutations in the ubiquinone biosynthetic pathway are increasingly being identified in patients. Furthermore, secondary ubiquinone deficiency is a common finding associated with mitochondrial disorders and might exacerbate these conditions. Recent developments have suggested that ubiquinone biosynthesis occurs in discrete domains of the mitochondrial inner membrane close to ER-mitochondria contact sites. This spatial requirement for ubiquinone biosynthesis could be the link between secondary ubiquinone deficiency and mitochondrial dysfunction, which commonly results in loss of mitochondrial structural integrity.

The Paradox of Coenzyme Q10 in Aging

Coenzyme Q (CoQ) is an essential endogenously synthesized molecule that links different metabolic pathways to mitochondrial energy production thanks to its location in the mitochondrial inner membrane and its redox capacity, which also provide it with the capability to work as an antioxidant. Although defects in CoQ biosynthesis in human and mouse models cause CoQ deficiency syndrome, some animals models with particular defects in the CoQ biosynthetic pathway have shown an increase in life span, a fact that has been attributed to the concept of mitohormesis. Paradoxically, CoQ levels decline in some tissues in human and rodents during aging and coenzyme Q₁₀ (CoQ₁₀) supplementation has shown benefits as an anti-aging agent, especially under certain conditions associated with increased oxidative stress. Also, CoQ₁₀ has shown therapeutic benefits in aging-related disorders, particularly in cardiovascular and metabolic diseases. Thus, we discuss the paradox of health benefits due to a defect in the CoQ biosynthetic pathway or exogenous supplementation of CoQ₁₀.

Recombinant RquA catalyzes the in vivo conversion of ubiquinone to rhodoquinone in Escherichia coli and Saccharomyces cerevisiae

Terpenoid quinones are liposoluble redox-active compounds that serve as essential electron carriers and antioxidants. One such quinone, rhodoquinone (RQ), couples the respiratory electron transfer chain to the reduction of fumarate to facilitate anaerobic respiration. This mechanism allows RQ-synthesizing organisms to operate their respiratory chain using fumarate as a final electron acceptor. RQ biosynthesis is restricted to a handful of prokaryotic and eukaryotic organisms, and details of this biosynthetic pathway remain enigmatic. One gene, rquA, was discovered to be required for RQ biosynthesis in Rhodospirillum rubrum. However, the function of the gene product, RquA, has remained unclear. Here, using reverse genetics approaches, we demonstrate that RquA converts ubiquinone to RQ directly. We also demonstrate the first in vivo synthetic production of RQ in Escherichia coli and Saccharomyces cerevisiae, two organisms that do not natively produce RQ. These findings help clarify the complete RQ biosynthetic pathway in species which contain RquA homologs.

Investigation of candidate genes involved in the rhodoquinone biosynthetic pathway in Rhodospirillum rubrum

The lipophilic electron-transport cofactor rhodoquinone (RQ) facilitates anaerobic metabolism in a variety of bacteria and selected eukaryotic organisms in hypoxic environments. We have shown that an intact rquA gene in Rhodospirillum rubrum is required for RQ production and efficient growth of the bacterium under anoxic conditions. While the explicit details of RQ biosynthesis have yet to be fully delineated, ubiquinone (Q) is a required precursor to RQ in R. rubrum, and the RquA gene product is homologous to a class I methyltransferase. In order to identify any additional requirements for RQ biosynthesis or factors influencing RQ production in R. rubrum, we performed transcriptome analysis to identify differentially expressed genes in anoxic, illuminated R. rubrum cultures, compared with those aerobically grown in the dark. To further select target genes, we employed a bioinformatics approach to assess the likelihood that a given differentially expressed gene under anoxic conditions may also have a direct role in RQ production or regulation of its levels in vivo. Having thus compiled a list of candidate genes, nine were chosen for further study by generation of knockout strains. RQ and Q levels were quantified using liquid chromatography-mass spectrometry, and rquA gene expression was measured using the real-time quantitative polymerase chain reaction. In one case, Q and RQ levels were decreased relative to wild type; in another case, the opposite effect was observed. These results comport with the crucial roles of rquA and Q in RQ biosynthesis, and reveal the existence of potential modulators of RQ levels in R. rubrum.

Human COQ10A and COQ10B are distinct lipid-binding START domain proteins required for coenzyme Q function

Coenzyme Q (CoQ or ubiquinone) serves as an essential redox-active lipid in respiratory electron and proton transport during cellular energy metabolism. CoQ also functions as a membrane-localized antioxidant protecting cells against lipid peroxidation. CoQ deficiency is associated with multiple human diseases; CoQ₁₀ supplementation in particular has noted cardioprotective benefits. In Saccharomyces cerevisiae, Coq10, a putative START domain protein, is believed to chaperone CoQ to sites where it functions. Yeast coq10 deletion mutants (coq10Δ) synthesize CoQ inefficiently during log phase growth and are respiratory defective and sensitive to oxidative stress. Humans have two orthologs of yeast COQ10, COQ10A and COQ10B Here, we tested the human co-orthologs for their ability to rescue the yeast mutant. We showed that expression of either human ortholog, COQ10A or COQ10B, rescues yeast coq10Δ mutant phenotypes, restoring the function of respiratory-dependent growth on a nonfermentable carbon source and sensitivity to oxidative stress induced by treatment with PUFAs. These effects indicate a strong functional conservation of Coq10 across different organisms. However, neither COQ10A nor COQ10B restored CoQ biosynthesis when expressed in the yeast coq10Δ mutant. The involvement of yeast Coq10 in CoQ biosynthesis may rely on its interactions with another protein, possibly Coq11, which is not found in humans. Coexpression analyses of yeast COQ10 and human COQ10A and COQ10B provide additional insights to functions of these START domain proteins and their potential roles in other biologic pathways.

CoQ10 production in Schizosaccharomyces pombe is increased by reduction of glucose levels or deletion of pka1

Coenzyme Q (CoQ) is an essential component of the electron transport system that produces ATP in nearly all living cells. CoQ₁₀ is a popular commercial food supplement around the world, and demand for efficient production of this molecule has increased in recent years. In this study, we explored CoQ₁₀ production in the fission yeast Schizosaccharomyces pombe. We found that CoQ₁₀ level was higher in stationary phase than in log phase, and that it increased when the cells were grown in a low concentration of glucose, in maltose, or in glycerol/ethanol medium. Because glucose signaling is mediated by cAMP, we evaluated the involvement of this pathway in CoQ biosynthesis. Loss of Pka1, the catalytic subunit of cAMP-dependent protein kinase, increased production of CoQ₁₀, whereas loss of the regulatory subunit Cgs1 decreased production. Manipulation of other components of the cAMP-signaling pathway affected CoQ₁₀ production in a consistent manner. We also found that glycerol metabolism was controlled by the cAMP/PKA pathway. CoQ₁₀ production by the S. pombe ∆pka1 reached 0.98 mg/g dry cell weight in medium containing a non-fermentable carbon source [2% glycerol (w/v) and 1% ethanol (w/v) supplemented with 0.5% casamino acids (w/v)], twofold higher than the production in wild-type cells under normal growth conditions. These findings demonstrate that carbon source, growth phase, and the cAMP-signaling pathway are important factors in CoQ₁₀ production in S. pombe.

Coenzyme Q biosynthetic proteins assemble in a substrate-dependent manner into domains at ER-mitochondria contacts

Coenzyme Q (CoQ) lipids are ancient electron carriers that, in eukaryotes, function in the mitochondrial respiratory chain. In mitochondria, CoQ lipids are built by an inner membrane-associated, multicomponent, biosynthetic pathway via successive steps of isoprenyl tail polymerization, 4-hydroxybenzoate head-to-tail attachment, and head modification, resulting in the production of CoQ. In yeast, we discovered that head-modifying CoQ pathway components selectively colocalize to multiple resolvable domains in vivo, representing supramolecular assemblies. In cells engineered with conditional ON or OFF CoQ pathways, domains were strictly correlated with CoQ production and substrate flux, respectively, indicating that CoQ lipid intermediates are required for domain formation. Mitochondrial CoQ domains were also observed in human cells, underscoring their conserved functional importance. CoQ domains within cells were highly enriched adjacent to ER-mitochondria contact sites. Together, our data suggest that CoQ domains function to facilitate substrate accessibility for processive and efficient CoQ production and distribution in cells.

The Endoplasmic Reticulum-Mitochondria Encounter Structure Complex Coordinates Coenzyme Q Biosynthesis

Loss of the endoplasmic reticulum (ER)-mitochondria encounter structure (ERMES) complex that resides in contact sites between the yeast ER and mitochondria leads to impaired respiration; however, the reason for that is not clear. We find that in ERMES null mutants, there is an increase in the level of mRNAs encoding for biosynthetic enzymes of coenzyme Q₆ (CoQ₆), an essential electron carrier of the mitochondrial respiratory chain. We show that the mega complexes involved in CoQ₆ biosynthesis (CoQ synthomes) are destabilized in ERMES mutants. This, in turn, affects the level and distribution of CoQ₆ within the cell, resulting in reduced mitochondrial CoQ₆. We suggest that these outcomes contribute to the reduced respiration observed in ERMES mutants. Fluorescence microscopy experiments demonstrate close proximity between the CoQ synthome and ERMES, suggesting a spatial coordination. The involvement of the ER-mitochondria contact site in regulation of CoQ₆ biogenesis highlights an additional level of communication between these two organelles.

Functional genetic discovery of enzymes using full-scan mass spectrometry metabolomics

Our understanding of metabolic networks is incomplete, and new enzymatic activities await discovery in well-studied organisms. Mass spectrometric measurement of cellular metabolites reveals compounds inside cells that are unexplained by current maps of metabolic reactions, and existing computational models are unable to account for all activities observed within cells. Additional large-scale genetic and biochemical approaches are required to elucidate metabolic gene function. We have used full-scan mass spectrometry metabolomics of polar small molecules to examine deletion mutants of candidate enzymes in the model yeast Saccharomyces cerevisiae. We report the identification of 25 genes whose deletion results in focal metabolic changes consistent with loss of enzymatic activity and describe the informatic approaches used to enrich for candidate enzymes from uncharacterized open reading frames. Triumphs and pitfalls of metabolic phenotyping screens are discussed, including estimates of the frequency of uncharacterized eukaryotic genes that affect metabolism and key issues to consider when searching for new enzymatic functions in other organisms.

A Soluble Metabolon Synthesizes the Isoprenoid Lipid Ubiquinone

Ubiquinone (UQ) is a polyprenylated lipid that is conserved from bacteria to humans and is crucial to cellular respiration. How the cell orchestrates the efficient synthesis of UQ, which involves the modification of extremely hydrophobic substrates by multiple sequential enzymes, remains an unresolved issue. Here, we demonstrate that seven Ubi proteins form the Ubi complex, a stable metabolon that catalyzes the last six reactions of the UQ biosynthetic pathway in Escherichia coli. The SCP2 domain of UbiJ forms an extended hydrophobic cavity that binds UQ intermediates inside the 1-MDa Ubi complex. We purify the Ubi complex from cytoplasmic extracts and demonstrate that UQ biosynthesis occurs in this fraction, challenging the current thinking of a membrane-associated biosynthetic process. Collectively, our results document a rare case of stable metabolon and highlight how the supramolecular organization of soluble enzymes allows the modification of hydrophobic substrates in a hydrophilic environment.

Insights into an Ancient Atypical Kinase Essential for Biosynthesis of Coenzyme Q

COQ8 proteins are homologs of atypical protein kinases required for the biosynthesis of coenzyme Q (CoQ). In this issue of Cell Chemical Biology, Reidenbach et al. (2018) show that COQ8 has an ATPase activity, required for CoQ biosynthesis, that is strongly activated by cardiolipin and small molecule mimics of early CoQ intermediates.

Reduction in the levels of CoQ biosynthetic proteins is related to an increase in lifespan without evidence of hepatic mitohormesis

Mitohormesis is an adaptive response induced by a mild mitochondrial stress that promotes longevity and metabolic health in different organisms. This mechanism has been proposed as the cause of the increase in the survival in Coq7^+/- (Mclk1^+/-) mice, which show hepatic reduction of COQ7, early mitochondrial dysfunction and increased oxidative stress. Our study shows that the lack of COQ9 in Coq9^Q95X mice triggers the reduction of COQ7, COQ6 and COQ5, which results in an increase in life expectancy. However, our results reveal that the hepatic CoQ levels are not decreased and, therefore, neither mitochondrial dysfunction or increased oxidative stress are observed in liver of Coq9^Q95X mice. These data point out the tissue specific differences in CoQ biosynthesis. Moreover, our results suggest that the effect of reduced levels of COQ7 on the increased survival in Coq9^Q95X mice may be due to mitochondrial mechanisms in non-liver tissues or to other unknown mechanisms.

Clinical syndromes associated with Coenzyme Q10 deficiency

Primary Coenzyme Q deficiencies represent a group of rare conditions caused by mutations in one of the genes required in its biosynthetic pathway at the enzymatic or regulatory level. The associated clinical manifestations are highly heterogeneous and mainly affect central and peripheral nervous system, kidney, skeletal muscle and heart. Genotype–phenotype correlations are difficult to establish, mainly because of the reduced number of patients and the large variety of symptoms. In addition, mutations in the same COQ gene can cause different clinical pictures. Here, we present an updated and comprehensive review of the clinical manifestations associated with each of the pathogenic variants causing primary CoQ deficiencies.

Coenzyme Q10 deficiencies: pathways in yeast and humans

Coenzyme Q (ubiquinone or CoQ) is an essential lipid that plays a role in mitochondrial respiratory electron transport and serves as an important antioxidant. In human and yeast cells, CoQ synthesis derives from aromatic ring precursors and the isoprene biosynthetic pathway. Saccharomyces cerevisiae coq mutants provide a powerful model for our understanding of CoQ biosynthesis. This review focusses on the biosynthesis of CoQ in yeast and the relevance of this model to CoQ biosynthesis in human cells. The COQ1–COQ11 yeast genes are required for efficient biosynthesis of yeast CoQ. Expression of human homologs of yeast COQ1–COQ10 genes restore CoQ biosynthesis in the corresponding yeast coq mutants, indicating profound functional conservation. Thus, yeast provides a simple yet effective model to investigate and define the function and possible pathology of human COQ (yeast or human gene involved in CoQ biosynthesis) gene polymorphisms and mutations. Biosynthesis of CoQ in yeast and human cells depends on high molecular mass multisubunit complexes consisting of several of the COQ gene products, as well as CoQ itself and CoQ intermediates. The CoQ synthome in yeast or Complex Q in human cells, is essential for de novo biosynthesis of CoQ. Although some human CoQ deficiencies respond to dietary supplementation with CoQ, in general the uptake and assimilation of this very hydrophobic lipid is inefficient. Simple natural products may serve as alternate ring precursors in CoQ biosynthesis in both yeast and human cells, and these compounds may act to enhance biosynthesis of CoQ or may bypass certain deficient steps in the CoQ biosynthetic pathway.

Biosynthesis and applications of prenylquinones

Prenylquinones are isoprenoid compounds with a characteristic quinone structure and isoprenyl tail that are ubiquitous in almost all living organisms. There are four major prenylquinone classes: ubiquinone (UQ), menaquinone (MK), plastoquinone (PQ), and rhodoquinone (RQ). The quinone structure and isoprenyl tail length differ among organisms. UQ, PQ, and RQ contain benzoquinone, while MK contains naphthoquinone. UQ, MK, and RQ are involved in oxidative phosphorylation, while PQ functions in photosynthetic electron transfer. Some organisms possess two types of prenylquinones; Escherichia coli has UQ₈ and MK₈, and Caenorhabditis elegans has UQ₉ and RQ₉. Crystal structures of most of the enzymes involved in MK synthesis have been solved. Studies on the biosynthesis and functions of quinones have advanced recently, including for phylloquinone (PhQ), which has a phytyl moiety instead of an isoprenyl tail. Herein, the synthesis and applications of prenylquinones are reviewed.

Coenzyme Q10 Supplementation in Aging and Disease

Coenzyme Q (CoQ) is an essential component of the mitochondrial electron transport chain and an antioxidant in plasma membranes and lipoproteins. It is endogenously produced in all cells by a highly regulated pathway that involves a mitochondrial multiprotein complex. Defects in either the structural and/or regulatory components of CoQ complex or in non-CoQ biosynthetic mitochondrial proteins can result in a decrease in CoQ concentration and/or an increase in oxidative stress. Besides CoQ₁₀ deficiency syndrome and aging, there are chronic diseases in which lower levels of CoQ₁₀ are detected in tissues and organs providing the hypothesis that CoQ₁₀ supplementation could alleviate aging symptoms and/or retard the onset of these diseases. Here, we review the current knowledge of CoQ₁₀ biosynthesis and primary CoQ₁₀ deficiency syndrome, and have collected published results from clinical trials based on CoQ₁₀ supplementation. There is evidence that supplementation positively affects mitochondrial deficiency syndrome and the symptoms of aging based mainly on improvements in bioenergetics. Cardiovascular disease and inflammation are alleviated by the antioxidant effect of CoQ₁₀. There is a need for further studies and clinical trials involving a greater number of participants undergoing longer treatments in order to assess the benefits of CoQ₁₀ treatment in metabolic syndrome and diabetes, neurodegenerative disorders, kidney diseases, and human fertility.

Schizosaccharomyces japonicus has low levels of CoQ10 synthesis, respiration deficiency, and efficient ethanol production

Coenzyme Q (CoQ) is essential for mitochondrial respiration and as a cofactor for sulfide quinone reductase. Schizosaccharomyces pombe produces a human-type CoQ₁₀. Here, we analyzed CoQ in other fission yeast species. S. cryophilus and S. octosporus produce CoQ₉. S. japonicus produces low levels of CoQ₁₀, although all necessary genes for CoQ synthesis have been identified in its genome. We expressed three genes (dps1, dlp1, and ppt1) for CoQ synthesis from S. japonicus in the corresponding S. pombe mutants, and confirmed that they were functional. S. japonicus had very low levels of oxygen consumption and was essentially respiration defective, probably due to mitochondrial dysfunction. S. japonicus grows well on minimal medium during anaerobic culture, indicating that it acquires sufficient energy by fermentation. S. japonicus produces comparable levels of ethanol under both normal and elevated temperature (42 °C) conditions, at which S. pombe is not able to grow.

Biochemistry of Mitochondrial Coenzyme Q Biosynthesis

Coenzyme Q (CoQ, ubiquinone) is a redox-active lipid produced across all domains of life that functions in electron transport and oxidative phosphorylation and whose deficiency causes human diseases. Yet, CoQ biosynthesis has not been fully defined in any organism. Several proteins with unclear molecular functions facilitate CoQ biosynthesis through unknown means, and multiple steps in the pathway are catalyzed by currently unidentified enzymes. Here we highlight recent progress toward filling these knowledge gaps through both traditional biochemistry and cutting-edge 'omics' approaches. To help fill the remaining gaps, we present questions framed by the recently discovered CoQ biosynthetic complex and by putative biophysical barriers. Mapping CoQ biosynthesis, metabolism, and transport pathways has great potential to enhance treatment of numerous human diseases.

Chromatin-remodeling SWI/SNF complex regulates coenzyme Q6 synthesis and a metabolic shift to respiration in yeast

Despite its relatively streamlined genome, there are many important examples of regulated RNA splicing in Saccharomyces cerevisiae Here, we report a role for the chromatin remodeler SWI/SNF in respiration, partially via the regulation of splicing. We find that a nutrient-dependent decrease in Snf2 leads to an increase in splicing of the PTC7 transcript. The spliced PTC7 transcript encodes a mitochondrial phosphatase regulator of biosynthesis of coenzyme Q₆ (ubiquinone or CoQ₆) and a mitochondrial redox-active lipid essential for electron and proton transport in respiration. Increased splicing of PTC7 increases CoQ₆ levels. The increase in PTC7 splicing occurs at least in part due to down-regulation of ribosomal protein gene expression, leading to the redistribution of spliceosomes from this abundant class of intron-containing RNAs to otherwise poorly spliced transcripts. In contrast, a protein encoded by the nonspliced isoform of PTC7 represses CoQ₆ biosynthesis. Taken together, these findings uncover a link between Snf2 expression and the splicing of PTC7 and establish a previously unknown role for the SWI/SNF complex in the transition of yeast cells from fermentative to respiratory modes of metabolism.

Human COQ9 Rescues a coq9 Yeast Mutant by Enhancing Coenzyme Q Biosynthesis from 4-Hydroxybenzoic Acid and Stabilizing the CoQ-Synthome

Coq9 is required for the stability of a mitochondrial multi-subunit complex, termed the CoQ-synthome, and the deamination step of Q intermediates that derive from para-aminobenzoic acid (pABA) in yeast. In human, mutations in the COQ9 gene cause neonatal-onset primary Q₁₀ deficiency. In this study, we determined whether expression of human COQ9 could complement yeast coq9 point or null mutants. We found that expression of human COQ9 rescues the growth of the temperature-sensitive yeast mutant, coq9-ts19, on a non-fermentable carbon source and increases the content of Q₆, by enhancing Q biosynthesis from 4-hydroxybenzoic acid (4HB). To study the mechanism for the rescue by human COQ9, we determined the steady-state levels of yeast Coq polypeptides in the mitochondria of the temperature-sensitive yeast coq9 mutant expressing human COQ9. We show that the expression of human COQ9 significantly increased steady-state levels of yeast Coq4, Coq6, Coq7, and Coq9 at permissive temperature. Human COQ9 polypeptide levels persisted at non-permissive temperature. A small amount of the human COQ9 co-purified with tagged Coq6, Coq6-CNAP, indicating that human COQ9 interacts with the yeast Q-biosynthetic complex. These findings suggest that human COQ9 rescues the yeast coq9 temperature-sensitive mutant by stabilizing the CoQ-synthome and increasing Q biosynthesis from 4HB. This finding provides a powerful approach to studying the function of human COQ9 using yeast as a model.