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.[1] 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.[1]
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.[1]
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 (ΔΨm) occurs with submicromolar doses of Tat, and cytochrome c is released from the mitochondria.[7]
↑Hey Y, Hoggard N, Burt E, James LA, Varley JM (Sep 1997). "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. doi:10.1159/000134565. PMID9284905.
↑Voet D, Voet JG, Pratt CW (2013). "Chapter 18". Fundamentals of biochemistry: life at the molecular level (4th ed.). Hoboken, NJ: Wiley. pp. 581–620. ISBN978-0-470-54784-7.
Hochstrasser DF, Frutiger S, Paquet N, Bairoch A, Ravier F, Pasquali C, Sanchez JC, Tissot JD, Bjellqvist B, Vargas R (Dec 1992). "Human liver protein map: a reference database established by microsequencing and gel comparison". Electrophoresis. 13 (12): 992–1001. doi:10.1002/elps.11501301201. PMID1286669.
Fabrizi GM, Sadlock J, Hirano M, Mita S, Koga Y, Rizzuto R, Zeviani M, Schon EA (Oct 1992). "Differential expression of genes specifying two isoforms of subunit VIa of human cytochrome c oxidase". Gene. 119 (2): 307–12. doi:10.1016/0378-1119(92)90288-Z. PMID1327966.
Schmidt TR, Jaradat SA, Goodman M, Lomax MI, Grossman LI (Jun 1997). "Molecular evolution of cytochrome c oxidase: rate variation among subunit VIa isoforms". Molecular Biology and Evolution. 14 (6): 595–601. doi:10.1093/oxfordjournals.molbev.a025798. PMID9190060.
Merante F, Ling M, Duncan AM, Duff C, Robinson BH (Jun 1997). "Cloning, characterization, and chromosomal localization of human liver form cytochrome c oxidase subunit VIa related genes". Genome / National Research Council Canada = Génome / Conseil National De Recherches Canada. 40 (3): 325–31. doi:10.1139/g97-045. PMID9202413.
Wong-Riley M, Guo A, Bachman NJ, Lomax MI (Apr 2000). "Human COX6A1 gene: promoter analysis, cDNA isolation and expression in the monkey brain". Gene. 247 (1–2): 63–75. doi:10.1016/S0378-1119(00)00121-9. PMID10773445.