Prenyldiphosphate Synthase, Subunit 1 (PDSS1)
Total Page:16
File Type:pdf, Size:1020Kb
Related Commentary, page 587 Research article Prenyldiphosphate synthase, subunit 1 (PDSS1) and OH-benzoate polyprenyltransferase (COQ2) mutations in ubiquinone deficiency and oxidative phosphorylation disorders Julie Mollet,1 Irina Giurgea,1 Dimitri Schlemmer,1 Gustav Dallner,2 Dominique Chretien,1 Agnès Delahodde,3 Delphine Bacq,4 Pascale de Lonlay,1 Arnold Munnich,1 and Agnès Rötig1 1INSERM U781 and Department of Genetics, Hôpital Necker-Enfants Malades, Paris, France. 2Department of Molecular Medicine and Surgery, Karolinska Hospital, Karolinska Institutet, Stockholm, Sweden. 3Institut de Génétique et Microbiologie, UMR 8621 CNRS, Université Paris-Sud, Orsay, France. 4Centre National de Génotypage, Evry, France. Coenzyme Q10 (CoQ10) plays a pivotal role in oxidative phosphorylation (OXPHOS), as it distributes elec- trons among the various dehydrogenases and the cytochrome segments of the respiratory chain. We have identified 2 novel inborn errors of CoQ10 biosynthesis in 2 distinct families. In both cases, enzymologic studies showed that quinone-dependent OXPHOS activities were in the range of the lowest control values, while OXPHOS enzyme activities were normal. CoQ10 deficiency was confirmed by restoration of normal OXPHOS activities after addition of quinone. A genome-wide search for homozygosity in family 1 identified a region of chromosome 10 encompassing the gene prenyldiphosphate synthase, subunit 1 (PDSS1), which encodes the human ortholog of the yeast COQ1 gene, a key enzyme of CoQ10 synthesis. Sequencing of PDSS1 identi- fied a homozygous nucleotide substitution modifying a conserved amino acid of the protein (D308E). In the second family, direct sequencing of OH-benzoate polyprenyltransferase (COQ2), the human ortholog of the yeast COQ2 gene, identified a single base pair frameshift deletion resulting in a premature stop codon (c.1198delT, N401fsX415). Transformation of yeast Δcoq1 and Δcoq2 strains by mutant yeast COQ1 and mutant human COQ2 genes, respectively, resulted in defective growth on respiratory medium, indicating that these muta- tions are indeed the cause of OXPHOS deficiency. Introduction an autosomal recessive mode of inheritance. This has been dem- Oxidative phosphorylation (OXPHOS) deficiency constitutes a onstrated by recent reports of OH-benzoate polyprenyltransferase clinically and genetically heterogeneous group of inherited dis- (COQ2) and prenyldiphosphate synthase, subunit 2 (PDSS2) mutation eases. One of these diseases, coenzyme Q10 (CoQ10, ubiquinone) in 2 independent families (11, 12). deficiency, is a recently identified entity of particular theoreti- Little is known about CoQ10 biosynthesis in humans, but sev- cal and practical importance. CoQ10 transfers reducing equiva- eral genes have been identified in the human genome by homol- lents from various dehydrogenases to complex III (ubiquinone ogy with other organisms, especially the Saccharomyces cerevisiae cytochrome c reductase) and acts as a transmembrane hydrogen yeast (Figure 1). In the present study, in an inbred family with carrier. CoQ10 also plays a critical role in antioxidant defenses CoQ10 deficiency manifesting as a multisystem disease with (1). Primary CoQ10 deficiency is a rare, but possibly treatable, early-onset deafness, encephaloneuropathy, obesity, livedo retic- autosomal recessive condition with 3 major clinical presenta- ularis, and valvulopathy, homozygosity mapping allowed the tions: (a) an encephalomyopathic form, characterized by exercise disease to be attributed to a homozygous missense mutation in intolerance, mitochondrial myopathy, myoglobinuria, epilepsy, PDSS1, the enzyme that elongates the prenyl side chain of coen- and ataxia (2–5); (b) a generalized infantile variant with severe zyme Q. Moreover, direct sequencing of various genes involved encephalopathy and renal disease (6–8); and (c) an ataxic form, in ubiquinone biosynthesis in an unrelated patient with fatal dominated by ataxia, seizures, cerebral atrophy, and/or anoma- infantile multiorgan disease detected a homozygous single base lies of the basal ganglia (9, 10). Recurrence of the disease and/or pair frameshift deletion in COQ2. This study extends our under- consanguinity of the parents in some reported families suggest standing of this newly recognized and possibly treatable cause of OXPHOS deficiency in humans. Nonstandard abbreviations used: COQ2, OH-benzoate polyprenyltransferase; CoQ10, Results coenzyme Q10; DQ, decylubiquinone; FPP, farnesylpyrophosphate; G3PDH, glycerol 3 phosphate dehydrogenase; GPP, geranylpyrophosphate; OXPHOS, oxidative phos- Enzymologic studies and quinone quantification. Assessment of indi- phorylation; PDSS1, prenyldiphosphate synthase, subunit 1; PP, pyrophosphate. vidual OXPHOS enzyme activities in cultured skin fibroblasts of Conflict of interest: The authors have declared that no conflict of interest exists. patient 1 revealed normal activity of complex II, complex III, and Citation for this article: J. Clin. Invest. 117:765–772 (2007). doi:10.1172/JCI29089. complex IV (Table 1). However, quinone-dependent activities The Journal of Clinical Investigation http://www.jci.org Volume 117 Number 3 March 2007 765 research article Figure 1 CoQ10 biosynthesis pathway. Enzyme and human gene symbols are shown in italics. The yeast gene symbol is indicated when different from the human gene. (CII+CIII, glycerol 3 phosphate dehydrogenase [G3PDH]+CIII) Finally, respiratory chain enzyme analysis in the liver of patient were in the range of the lowest control values, and activity ratios 3 revealed normal absolute enzyme activities but increased CIV/ (CIV/CII+CIII, CII+CIII/G3PDH+CIII), which optimally detect CII+CIII and CIV/CI+CIII activity ratios, also suggesting qui- unbalanced respiratory chain enzyme functions, were markedly none deficiency (Table 1). altered compared with controls, suggesting quinone deficiency. Direct evidence of quinone deficiency was finally provided by Muscle mitochondria of patient 1 showed high absolute activity quantification of CoQ10 in the patients’ fibroblasts, as the CoQ10 values for all complexes (Table 1) but abnormal activity ratios content of the 3 patients’ fibroblasts was markedly decreased (CI+CIII/CI, CIII/CI+CIII), also indicating quinone deficiency. compared with normal values (Table 2). Interestingly, a normal The hypothesis of ubiquinone deficiency was further supported CoQ9 level was found in patients 1 and 2. The markedly decreased by the dramatic effect of decylubiquinone (DQ, an exogenous CoQ10/CoQ9 ratio in patients 1 and 2 (0.3; controls: 13 ± 3) sug- ubiquinone analog) on succinate oxidation of fibroblasts from gested a defective addition of the tenth prenyl to the polyprenyl patient 1, as addition of DQ during succinate oxidation mea- chain. Fibroblasts from controls and patient 3 were grown in the surement restored normal activity (8 and 16 nmol/min/mg pro- presence of [3H]mevalonate to estimate the ability of these cells to 3 tein before and after DQ addition, respectively; normal values: synthesize CoQ10. Substantial incorporation of [ H]mevalonate 9.8–20.5 nmol/min/mg protein) in the patient’s permeabilized into cholesterol, squalene, and dolichol was detected in controls 3 fibroblasts (Figure 2A). Consistently, addition of DQ during and patient 3, but no [ H]CoQ10 was detected in cultured skin measurement of succinate–cytochrome c reductase activity fibroblasts from patient 3 (Figure 2C). In these experiments, restored normal activity of cultured skin fibroblasts (19 and all lipid extracts were treated with acid phosphatase to dephos- 44 nmol/min/mg protein before and after DQ addition, respec- phorylate accumulated intermediates. In patient 3, a peak with tively; normal values: 22–47 nmol/min/mg protein; Figure 2B). a retention time of 18.5 minutes was observed and was identi- 766 The Journal of Clinical Investigation http://www.jci.org Volume 117 Number 3 March 2007 research article Table 1 a glutamic acid (D308E). This aspartic acid Respiratory chain enzyme activities in muscle mitochondria and cultured skin fibroblasts is also conserved in eukaryote and prokary- ote farnesylpyrophosphate (FPP) synthases Enzyme Patient 1 Patient 1 Patient 3 and geranylpyrophosphate (GPP) synthases Cultured skin Muscle Liver (13–15). Moreover, this aspartic acid lies in fibroblasts mitochondria homogenate the signature pattern of polyprenyl synthase Activities (nmol/min/mg protein) ([LIVMFY]-G-x(2)-[FYL]-Q-[LIVM]-x-D-D- CI – 279 (65.2 ± 16.6) 33 (28.6 ± 6.3) [LIVMFY]-x-[DNG]), an aspartic acid–rich CII 14 (20.1 ± 3.5) – 202 (158.5 ± 28.1) region of the protein that could be involved CIII 123 (169.6 ± 37.5) 3,838 (1,258.8 ± 327.5) 327 (250.8 ± 40.6) in the catalytic mechanism and/or binding CIV 93 (107.1 ± 25.6) 1,827 (730.3 ± 233.4) 364 (270.6 ± 48.3) of the substrates (Figure 4E). Both parents CV – – 114 (96.2 ± 32.1) were heterozygous for the T→G transversion CI+CIII – 414 (199 ± 56.4) 25 (67.5 ± 16.5) (Figure 4B), and unaffected children were CII+CIII 19 (33.4 ± 6.7) 596 (228.8 ± 61.8) 25 (69.5 ± 15.4) either heterozygous or homozygous for the G3PDH 13 (14.4 ± 2.5) – – wild-type allele. The T→G transversion creat- G3PDH+CIII 5 (18.2 ± 3.5) 43 (38.6 ± 11.6) – ed an MnlI restriction site. Exon 10 was ampli- CS 71 (77 ± 20.7) 139 (324.1 ± 92.9) 74 (102.5 ± 15.9) fied, and the PCR product was then digested Activity ratios by the restriction enzyme MnlI. This gener- CIV/CI – 4.4 (3.5 ± 0.9) 11 (8.8 ± 1.8) ated 2 fragments in controls (393 and 180 bp) CIV/CII 6.6 (5 ± 0.5)