Summary: Bacterial aa3 type cytochrome c oxidase subunit IV
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Cytochrome c oxidase Edit Wikipedia article
|Cytochrome c oxidase|
|PDB structures||RCSB PDB PDBe PDBsum|
|Gene Ontology||AmiGO / EGO|
It is the last enzyme in the respiratory electron transport chain of mitochondria (or bacteria) located in the mitochondrial (or bacterial) membrane. It receives an electron from each of four cytochrome c molecules, and transfers them to one oxygen molecule, converting molecular oxygen to two molecules of water. In the process, it binds four protons from the inner aqueous phase to make water, and in addition translocates four protons across the membrane, helping to establish a transmembrane difference of proton electrochemical potential that the ATP synthase then uses to synthesize ATP.
The complex is a large integral membrane protein composed of several metal prosthetic sites and 14  protein subunits in mammals. In mammals, eleven subunits are nuclear in origin, and three are synthesized in the mitochondria. The complex contains two hemes, a cytochrome a and cytochrome a3, and two copper centers, the CuA and CuB centers. In fact, the cytochrome a3 and CuB form a binuclear center that is the site of oxygen reduction. Cytochrome c, which is reduced by the preceding component of the respiratory chain (cytochrome bc1 complex, complex III), docks near the CuA binuclear center and passes an electron to it, being oxidized back to cytochrome c containing Fe3+. The reduced CuA binuclear center now passes an electron on to cytochrome a, which in turn passes an electron on to the cytochrome a3-CuB binuclear center. The two metal ions in this binuclear center are 4.5 Å apart and coordinate a hydroxide ion in the fully oxidized state.
Crystallographic studies of cytochrome c oxidase show an unusual post-translational modification, linking C6 of Tyr(244) and the ε-N of His(240) (bovine enzyme numbering). It plays a vital role in enabling the cytochrome a3- CuB binuclear center to accept four electrons in reducing molecular oxygen to water. The mechanism of reduction was formerly thought to involve a peroxide intermediate, which was believed to lead to superoxide production. However, the currently accepted mechanism involves a rapid four-electron reduction involving immediate oxygen-oxygen bond cleavage, avoiding any intermediate likely to form superoxide.
Site of assembly is believed to occur near TOM/TIM, where complex intermediates are accessible to bind with subunits imported from cytosol. Hemes and cofactors are inserted into subunits I & II. Subunits I and IV initiate assembly. Other subunits may form sub-complex intermediates that later bind to others to form COX complex. In post-assembly modifications, the enzyme is dimerized, which is required for active/efficient enzyme action. Dimers are connected by a cardiolipin molecule.
- 4 Fe2+-cytochrome c + 8 H+in + O2 → 4 Fe3+-cytochrome c + 2 H2O + 4 H+out
Two electrons are passed from two cytochrome c's, through the CuA and cytochrome a sites to the cytochrome a3- CuB binuclear center, reducing the metals to the Fe2+ form and Cu+. The hydroxide ligand is protonated and lost as water, creating a void between the metals that is filled by O2. The oxygen is rapidly reduced, with two electrons coming from the Fe2+cytochrome a3, which is converted to the ferryl oxo form (Fe4+=O). The oxygen atom close to CuB picks up one electron from Cu+, and a second electron and a proton from the hydroxyl of Tyr(244), which becomes a tyrosyl radical: The second oxygen is converted to a hydroxide ion by picking up two electrons and a proton. A third electron arising from another cytochrome c is passed through the first two electron carriers to the cytochrome a3- CuB binuclear center, and this electron and two protons convert the tyrosyl radical back to Tyr, and the hydroxide bound to CuB2+ to a water molecule. The fourth electron from another cytochrome c flows through CuA and cytochrome a to the cytochrome a3- CuB binuclear center, reducing the Fe4+=O to Fe3+, with the oxygen atom picking up a proton simultaneously, regenerating this oxygen as a hydroxide ion coordinated in the middle of the cytochrome a3- CuB center as it was at the start of this cycle. The net process is that four reduced cytochrome c's are used, along with 4 protons, to reduce O2 to two water molecules.
Cyanide, sulfide, azide, and carbon monoxide all bind to cytochrome c oxidase, thus competitively inhibiting the protein from functioning, which results in chemical asphyxiation of cells. Methanol in methylated spirits is converted into formic acid, which also inhibits the same oxidase system.
Subcellular Localization and Presence at Extramitochondrial Sites
Cytochrome c oxidase has 3 subunits which are encoded by mitochondrial DNA. Of these 3 subunits encoded by mitochondrial DNA, two have been identified in extramitochondrial locations. In pancreatic acinar tissue, these subunits were found in zymogen granules. Additionally, in the anterior pituitary, relatively high amounts of these subunits were found in growth hormone secretory granules. The extramitochondrial function of these cytochrome c oxidase subunits has not yet been characterized. Besides cytochrome c oxidase subunits, extramitochondrial localization has also been observed for large numbers of other mitochondrial proteins., This raises the possibility about existence of yet unidentified specific mechanisms for protein translocation from mitochondria to other cellular destinations.
Genetic defects and disorders
Defects involving genetic mutations altering cytochrome c oxidase (COX) functionality or structure can result in severe, often fatal metabolic disorders. Such disorders usually manifest in early childhood and affect predominantly tissues with high energy demands (brain, heart, muscle). Among the many classified mitochondrial diseases, those involving dysfunctional COX assembly are thought to be the most severe.
The vast majority of COX disorders are linked to mutations in nuclear-encoded proteins referred to as assembly factors, or assembly proteins. These assembly factors contribute to COX structure and functionality, and are involved in several essential processes, including transcription and translation of mitochondrion-encoded subunits, processing of preproteins and membrane insertion, and cofactor biosynthesis and incorporation.
Currently, mutations have been identified in seven COX assembly factors: SURF1, SCO1, SCO2, COX10, COX15, COX20, COA5 and LRPPRC. Mutations in these proteins can result in altered functionality of sub-complex assembly, copper transport, or translational regulation. Each gene mutation is associated with the etiology of a specific disease, with some having implications in multiple disorders. Disorders involving dysfunctional COX assembly via gene mutations include Leigh syndrome, cardiomyopathy, leukodystrophy, anemia, and sensorineural deafness.
COX histochemistry is used for mapping regional brain metabolism in animals, since there is a direct relation between enzyme activity and neuronal activity. Such brain mapping has been accomplished in spontaneous mutant mice with cerebellar disease such as reeler and a transgenic model of Alzheimer's disease. This technique has also been used to map learning activity in animal brain.
- Cytochrome c oxidase subunit I
- Cytochrome c oxidase subunit II
- Cytochrome c oxidase subunit III
- Heme a
- Balsa E, Marco R, Perales-Clemente E, Szklarczyk R, Calvo E, Landázuri MO, Enríquez JA (September 2012). "NDUFA4 is a subunit of complex IV of the mammalian electron transport chain". Cell Metab. 16 (3): 378–86. doi:10.1016/j.cmet.2012.07.015. PMID 22902835.
- Tsukihara T, Aoyama H, Yamashita E, Tomizaki T, Yamaguchi H, Shinzawa-Itoh K, Nakashima R, Yaono R, Yoshikawa S (August 1995). "Structures of metal sites of oxidized bovine heart cytochrome c oxidase at 2.8 A". Science 269 (5227): 1069–74. doi:10.1126/science.7652554. PMID 7652554.
- Voet, Donald (2010). Biochemistry. New York: J. Wiley & Sons. pp. 865–866. ISBN 0-470-57095-4.
- Khalimonchuk O, Rödel G (December 2005). "Biogenesis of cytochrome c oxidase". Mitochondrion 5 (6): 363–88. doi:10.1016/j.mito.2005.08.002. PMID 16199211.
- Fontanesi F, Soto IC, Horn D, Barrientos A (December 2006). "Assembly of mitochondrial cytochrome c-oxidase, a complicated and highly regulated cellular process". Am. J. Physiol., Cell Physiol. 291 (6): C1129–47. doi:10.1152/ajpcell.00233.2006. PMID 16760263.
- Alonso JR, Cardellach F, López S, Casademont J, Miró O (September 2003). "Carbon monoxide specifically inhibits cytochrome c oxidase of human mitochondrial respiratory chain". Pharmacol. Toxicol. 93 (3): 142–6. doi:10.1034/j.1600-0773.2003.930306.x. PMID 12969439.
- Sadacharan, S. K., Singh, B., Bowes, T. and Gupta, R. S. (2005). Localization of mitochondrial DNA encoded cytochrome c oxidase subunits I and II in rat pancreatic zymogen granules and pituitary growth hormone granules. Histochem Cell Biol. 124:409-421.
- Gupta, R. S., Ramachandra, N. B., Bowes, T. and Singh, B. (2008) Unusual cellular disposition of the mitochondrial molecular chaperones Hsp60, Hsp70 and Hsp10. Novartis Found Symp. 291: 59-68.
- Soltys, B. J. and Gupta, R. S. (1999). Mitochondrial proteins at unexpected cellular locations: export of proteins from mitochondria from an evolutionary perspective. International Review of Cytology. 94:133-196.
- Soltys , B. J. and Gupta, R.S. (1999) Mitochondrial proteins at unexpected locations: Are they exported?" Trends Biochem. Sci 24: 174-177.
- Pecina P, Houstková H, Hansíková H, Zeman J, Houstek J (2004). "Genetic defects of cytochrome c oxidase assembly". Physiol Res. 53 Suppl 1: S213–23. PMID 15119951.
- Zee JM, Glerum DM (December 2006). "Defects in cytochrome oxidase assembly in humans: lessons from yeast". Biochem. Cell Biol. 84 (6): 859–69. doi:10.1139/o06-201. PMID 17215873.
- Wong-Riley MT. (1989). "Cytochrome oxidase: an endogenous metabolic marker for neuronal activity.". Trends Neurosci. 12 (3): 94–111. doi:10.1016/0166-2236(89)90165-3. PMID 2469224.
- Strazielle C, Hayzoun K, Derer M, Mariani J, Lalonde R. (April 2006). "Regional brain variations of cytochrome oxidase activity in Relnrl-orl mutant mice.". J. Neurosci. Res. 83 (5): 821–31. doi:10.1002/jnr.20772. PMID 16511878.
- Strazielle C, Sturchler-Pierrat C, Staufenbiel M, Lalonde R. (2003). "Regional brain cytochrome oxidase activity in beta-amyloid precursor protein transgenic mice with the Swedish mutation.". Neuroscience 118 (4): 1151–63. doi:10.1016/S0306-4522(03)00037-X. PMID 12732258.
- Conejo NM, González-Pardo H, Gonzalez-Lima F, Arias JL. (2010). "Spatial learning of the water maze: progression of brain circuits mapped with cytochrome oxidase histochemistry.". Neurobiol. Learn. Mem. 93 (3): 362–71. doi:10.1016/j.nlm.2009.12.002. PMID 19969098.
- The Cytochrome Oxidase home page at Rice University
- Interactive Molecular model of cytochrome c oxidase (Requires MDL Chime)
- UMich Orientation of Proteins in Membranes families/superfamily-4
- Cytochrome-c Oxidase at the US National Library of Medicine Medical Subject Headings (MeSH)
This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.
Bacterial aa3 type cytochrome c oxidase subunit IV Provide feedback
Bacterial cytochrome c oxidase is found bound to the to the cell membrane, where it is involved in the generation of the transmembrane proton electrochemical gradient. It is composed of four subunits. Subunit IV consists of one transmembrane helix that does not interact directly with the other subunits, but maintains its position by indirect contacts via phospholipid molecules found in the structure. The function of subunit IV is as yet unknown .
Svensson-Ek M, Abramson J, Larsson G, Tornroth S, Brzezinski P, Iwata S; , J Mol Biol 2002;321:329-339.: The X-ray crystal structures of wild-type and EQ(I-286) mutant cytochrome c oxidases from Rhodobacter sphaeroides. PUBMED:12144789 EPMC:12144789
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR012422
Bacterial cytochrome c oxidase is found bound to the to the cell membrane, where it is involved in the generation of the transmembrane proton electrochemical gradient. It is composed of four subunits. Subunit IV consists of one transmembrane helix that does not interact directly with the other subunits, but maintains its position by indirect contacts via phospholipid molecules found in the structure. The function of subunit IV is as yet unknown [PUBMED:12144789].
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|Seed source:||Pfam-B_86185 (release 14.0)|
|Number in seed:||36|
|Number in full:||225|
|Average length of the domain:||44.90 aa|
|Average identity of full alignment:||37 %|
|Average coverage of the sequence by the domain:||68.34 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||7|
|Download:||download the raw HMM for this family|
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There are 3 interactions for this family. More...
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For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the COX4_pro_2 domain has been found. There are 5 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.
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