title: Disruption of the human COQ5-containing protein complex is associated with diminished coenzyme Q10 levels under two different conditions of mitochondrial energy deficiency.
abstract: The Coq protein complex assembled from several Coq proteins is critical for coenzyme Q6 (CoQ6) biosynthesis in yeast. Secondary CoQ10 deficiency is associated with mitochondrial DNA (mtDNA) mutations in patients. We previously demonstrated that carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP) suppressed CoQ10 levels and COQ5 protein maturation in human 143B cells.
  
  
  
  This study explored the putative COQ protein complex in human cells through two-dimensional blue native-polyacrylamide gel electrophoresis and Western blotting to investigate its status in 143B cells after FCCP treatment and in cybrids harboring the mtDNA mutation that caused myoclonic epilepsy with ragged-red fibers (MERRF) syndrome. Ubiquinol-10 and ubiquinone-10 levels were detected by high-performance liquid chromatography. Mitochondrial energy status, mRNA levels of various PDSS and COQ genes, and protein levels of COQ5 and COQ9 in cybrids were examined.
  
  
  
  A high-molecular-weight protein complex containing COQ5, but not COQ9, in the mitochondria was identified and its level was suppressed by FCCP and in cybrids with MERRF mutation. That was associated with decreased mitochondrial membrane potential and mitochondrial ATP production. Total CoQ10 levels were decreased under both conditions, but the ubiquinol-10:ubiquinone-10 ratio was increased in mutant cybrids. The expression of COQ5 was increased but COQ5 protein maturation was suppressed in the mutant cybrids.
  
  
  
  A novel COQ5-containing protein complex was discovered in human cells. Its destabilization was associated with reduced CoQ10 levels and mitochondrial energy deficiency in human cells treated with FCCP or exhibiting MERRF mutation.
  
  
  
  The findings elucidate a possible mechanism for mitochondrial dysfunction-induced CoQ10 deficiency in human cells.
authors.affiliation: Graduate Institute and Department of Medical Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan; Department of Nephrology, Chang Gung Memorial Hospital, Taoyuan, Taiwan. Electronic address: yen@mail.cgu.edu.tw.
authors.forename: Hsiu-Chuan
authors.initials: HC
authors.lastname: Yen
authors.affiliation: Graduate Institute and Department of Medical Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Yi-Chun
authors.initials: YC
authors.lastname: Liu
authors.affiliation: Graduate Institute and Department of Medical Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Chia-Chi
authors.initials: CC
authors.lastname: Kan
authors.affiliation: Graduate Institute and Department of Medical Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Hsing-Ju
authors.initials: HJ
authors.lastname: Wei
authors.affiliation: Graduate Institute and Department of Medical Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Szu-Hsien
authors.initials: SH
authors.lastname: Lee
authors.affiliation: Department of Biochemistry and Molecular Biology, School of Life Sciences, National Yang Ming University, Taipei, Taiwan; Department of Medicine, Mackay Medical College, New Taipei City, Taiwan.
authors.forename: Yau-Huei
authors.initials: YH
authors.lastname: Wei
authors.affiliation: Graduate Institute and Department of Medical Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Yu-Hsiu
authors.initials: YH
authors.lastname: Feng
authors.affiliation: Graduate Institute and Department of Medical Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Chih-Wei
authors.initials: CW
authors.lastname: Chen
authors.affiliation: College of Medicine, Chang Gung University and Department of Neurology, Chang Gung Memorial Hospital, Taoyuan, Taiwan.
authors.forename: Chin-Chang
authors.initials: CC
authors.lastname: Huang
mesh_terms: D001259:Ataxia / Q000235:genetics / Q000378:metabolism; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002460:Cell Line; D004272:DNA, Mitochondrial / Q000235:genetics; D006801:Humans; D017243:MERRF Syndrome / Q000235:genetics / Q000378:metabolism*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000235:genetics; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D028361:Mitochondrial Diseases / Q000235:genetics / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D018908:Muscle Weakness / Q000235:genetics / Q000378:metabolism; D009154:Mutation / Q000187:drug effects / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000172:deficiency / Q000235:genetics / Q000378:metabolism
chemical_list: D004272:DNA, Mitochondrial; D024101:Mitochondrial Proteins; D012333:RNA, Messenger; D014451:Ubiquinone; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; C026663:ubiquinol-10; D008780:Methyltransferases; C583058:COQ5 protein, human; C024989:coenzyme Q10; C025204:Ubiquinone Q2; C030571:ubiquinone 9
keywords: Chemical uncoupler; High-molecular-weight protein complex; Human COQ5; Human COQ9; Secondary coenzyme Q(10) deficiency; mtDNA mutation