COX6A1 explained

Cytochrome c oxidase subunit 6A1, mitochondrial is a protein that in humans is encoded by the COX6A1 gene. Cytochrome c oxidase 6A1 is a subunit of the cytochrome c oxidase complex, also known as Complex IV, the last enzyme in the mitochondrial electron transport chain. A mutation of the COX6A1 gene is associated with a recessive axonal or mixed form of Charcot-Marie-Tooth disease.^{[1] [2]}

Structure

The COX6A1 gene, located on the q arm of chromosome 12 in position 24.2, contains 3 exons and is 2,653 base pairs in length. The COX6A1 protein weighs 12 kDa and is composed of 109 amino acids.^{[3] [4]} The protein is a subunit of Complex IV, a heteromeric complex consisting of 3 catalytic subunits encoded by mitochondrial genes and multiple structural subunits encoded by nuclear genes. This nuclear gene encodes polypeptide 1 (liver isoform) of subunit VIa, and polypeptide 1 is found in all non-muscle tissues. Polypeptide 2 (heart/muscle isoform) of subunit VIa is encoded by a different gene, COX6A2, and is present only in striated muscles. These two polypeptides share 66% amino acid sequence identity.

Function

Cytochrome c oxidase (COX) is the terminal enzyme of the mitochondrial respiratory chain. It is a multi-subunit enzyme complex that couples the transfer of electrons from cytochrome c to molecular oxygen and contributes to a proton electrochemical gradient across the inner mitochondrial membrane to drive ATP synthesis via protonmotive force. The mitochondrially-encoded subunits perform the electron transfer of proton pumping activities. The functions of the nuclear-encoded subunits are unknown but they may play a role in the regulation and assembly of the complex.

Summary reaction:

4 Fe²⁺-cytochrome c + 8 H⁺_in + O₂ → 4 Fe³⁺-cytochrome c + 2 H₂O + 4 H⁺_out^[5]

Clinical significance

A mutation leading to a 5 base pair deletion in the COX6A1 gene is associated with Charcot-Marie-Tooth disease (CMT). CMT is the most common inherited neuropathy and can result from mutations in over 30 different loci. Expression of COX6A1 is significantly reduced in affected individuals.^[6]

The Trans-activator of transcription protein (Tat) of human immunodeficiency virus (HIV) inhibits cytochrome c oxidase (COX) activity in permeabilized mitochondria isolated from both mouse and human liver, heart, and brain samples. Rapid loss of membrane potential (ΔΨ_m) occurs with submicromolar doses of Tat, and cytochrome c is released from the mitochondria.^[7]

Further reading

• Hochstrasser DF, Frutiger S, Paquet N, Bairoch A, Ravier F, Pasquali C, Sanchez JC, Tissot JD, Bjellqvist B, Vargas R . Human liver protein map: a reference database established by microsequencing and gel comparison . Electrophoresis . 13 . 12 . 992–1001 . Dec 1992 . 1286669 . 10.1002/elps.11501301201 . 23518983 .
• Fabrizi GM, Sadlock J, Hirano M, Mita S, Koga Y, Rizzuto R, Zeviani M, Schon EA . Differential expression of genes specifying two isoforms of subunit VIa of human cytochrome c oxidase . Gene . 119 . 2 . 307–12 . Oct 1992 . 1327966 . 10.1016/0378-1119(92)90288-Z .
• Fabrizi GM, Rizzuto R, Nakase H, Mita S, Kadenbach B, Schon EA . Sequence of a cDNA specifying subunit VIa of human cytochrome c oxidase . Nucleic Acids Research . 17 . 15 . 6409 . Aug 1989 . 2549515 . 318308 . 10.1093/nar/17.15.6409 .
• Schmidt TR, Jaradat SA, Goodman M, Lomax MI, Grossman LI . Molecular evolution of cytochrome c oxidase: rate variation among subunit VIa isoforms . Molecular Biology and Evolution . 14 . 6 . 595–601 . Jun 1997 . 9190060 . 10.1093/oxfordjournals.molbev.a025798 . free .
• Merante F, Ling M, Duncan AM, Duff C, Robinson BH . Cloning, characterization, and chromosomal localization of human liver form cytochrome c oxidase subunit VIa related genes . Genome . 40 . 3 . 325–31 . Jun 1997 . 9202413 . 10.1139/g97-045 .
• Wong-Riley M, Guo A, Bachman NJ, Lomax MI . Human COX6A1 gene: promoter analysis, cDNA isolation and expression in the monkey brain . Gene . 247 . 1–2 . 63–75 . Apr 2000 . 10773445 . 10.1016/S0378-1119(00)00121-9 .

External links

• Mass spectrometry characterization of COX6A1 at COPaKB

Notes and References

1. Web site: Entrez Gene: COX6A1 cytochrome c oxidase subunit VIa polypeptide 1.
2. Hey Y, Hoggard N, Burt E, James LA, Varley JM . Assignment of COX6A1 to 6p21 and a pseudogene (COX6A1P) to 1p31.1 by in situ hybridization and somatic cell hybrids . Cytogenetics and Cell Genetics . 77 . 3–4 . 167–8 . Sep 1997 . 9284905 . 10.1159/000134565 .
3. Zong NC, Li H, Li H, Lam MP, Jimenez RC, Kim CS, Deng N, Kim AK, Choi JH, Zelaya I, Liem D, Meyer D, Odeberg J, Fang C, Lu HJ, Xu T, Weiss J, Duan H, Uhlen M, Yates JR, Apweiler R, Ge J, Hermjakob H, Ping P . Integration of cardiac proteome biology and medicine by a specialized knowledgebase . Circulation Research . 113 . 9 . 1043–53 . Oct 2013 . 23965338 . 4076475 . 10.1161/CIRCRESAHA.113.301151 .
4. Web site: Cytochrome c oxidase subunit 6A1, mitochondrial . Cardiac Organellar Protein Atlas Knowledgebase (COPaKB) . 2018-07-18 . https://web.archive.org/web/20180720200700/https://amino.heartproteome.org/web/protein/P12074 . 2018-07-20 . dead .
5. Book: Donald . Voet . Judith G. . Voet . Charlotte W. . Pratt . vanc . Donald Voet . Judith G. Voet . Fundamentals of biochemistry: life at the molecular level . 2013 . Wiley . Hoboken, NJ . 978-0-470-54784-7 . Chapter 18 . 581–620 . 4th .
6. Tamiya G, Makino S, Hayashi M, Abe A, Numakura C, Ueki M, Tanaka A, Ito C, Toshimori K, Ogawa N, Terashima T, Maegawa H, Yanagisawa D, Tooyama I, Tada M, Onodera O, Hayasaka K . A mutation of COX6A1 causes a recessive axonal or mixed form of Charcot-Marie-Tooth disease . American Journal of Human Genetics . 95 . 3 . 294–300 . Sep 2014 . 25152455 . 4157141 . 10.1016/j.ajhg.2014.07.013 .
7. Lecoeur H, Borgne-Sanchez A, Chaloin O, El-Khoury R, Brabant M, Langonné A, Porceddu M, Brière JJ, Buron N, Rebouillat D, Péchoux C, Deniaud A, Brenner C, Briand JP, Muller S, Rustin P, Jacotot E . HIV-1 Tat protein directly induces mitochondrial membrane permeabilization and inactivates cytochrome c oxidase . Cell Death & Disease . 3 . 3 . e282 . 2012 . 22419111 . 3317353 . 10.1038/cddis.2012.21 .