PROSITE documentation PDOC00075 [for PROSITE entry PS50999]

Cytochrome c oxidase subunit II signature and profiles


Cytochrome c oxidase (EC [1,2] is an oligomeric enzymatic complex which is a component of the respiratory chain and is involved in the transfer of electrons from cytochrome c to oxygen. In eukaryotes this enzyme complex is located in the mitochondrial inner membrane; in aerobic prokaryotes it is found in the plasma membrane. The enzyme complex consists of 3-4 subunits (prokaryotes) to up to 13 polypeptides (mammals).

Subunit 2 (CO II) transfers the electrons from cytochrome c to the catalytic subunit 1. It contains two adjacent transmembrane regions in its N-terminus and the major part of the protein is exposed to the periplasmic or to the mitochondrial intermembrane space, respectively. CO II provides the substrate-binding site and contains a copper center called Cu(A), located in the extramembrane domain (see <PDB:1OCZ; B>), probably the primary acceptor in cytochrome c oxidase. An exception is the corresponding subunit of the cbb3-type oxidase which lacks the copper A redox-center. Several bacterial CO II have a C-terminal extension that contains a covalently bound heme c.

It has been shown [3,4] that nitrous oxide reductase (EC (gene nosZ) of Pseudomonas has sequence similarity in its C-terminus to CO II. This enzyme is part of the bacterial respiratory system which is activated under anaerobic conditions in the presence of nitrate or nitrous oxide. NosZ is a periplasmic homodimer that contains a dinuclear copper center, probably located in a 3-dimensional fold similar to the cupredoxin-like fold that has been suggested for the copper-binding site of CO II [3].

The dinuclear purple copper center is formed by 2 histidines and 2 cysteines [5]. We used this region as a signature pattern. The conserved valine and the conserved methionine are said to be involved in stabilizing the copper-binding fold by interacting with each other. We also developed two profiles, one directed against the transmembrane region and one against the copper center.


Cytochrome cbb(3) subunit 2 does not belong to this family.

Last update:

June 2004 / Text revised; profiles added.

Technical section

PROSITE methods (with tools and information) covered by this documentation:

COX2_TM, PS50999; Cytochrome oxidase subunit II transmembrane region profile  (MATRIX)

COX2_CUA, PS50857; Cytochrome oxidase subunit II copper A binding domain profile  (MATRIX)

COX2, PS00078; CO II and nitrous oxide reductase dinuclear copper centers signature  (PATTERN)


1AuthorsCapaldi R.A., Malatesta F., Darley-Usmar V.M.
TitleStructure of cytochrome c oxidase.
SourceBiochim. Biophys. Acta 726:135-148(1983).
PubMed ID6307356

2AuthorsGarcia-Horsman J.A., Barquera B., Rumbley J., Ma J., Gennis R.B.
SourceJ. Bacteriol. 176:5587-5600(1994).

3Authorsvan der Oost J., Lappalainen P., Musacchio A., Warne A., Lemieux L., Rumbley J., Gennis R.B., Aasa R., Pascher T., Malmstrom B.G., Saraste M.
SourceEMBO J. 11:3209-3217(1992).

4AuthorsZumft W.G., Dreusch A., Lochelt S., Cuypers H., Friedrich B., Schneider B.
TitleDerived amino acid sequences of the nosZ gene (respiratory N2O reductase) from Alcaligenes eutrophus, Pseudomonas aeruginosa and Pseudomonas stutzeri reveal potential copper-binding residues. Implications for the CuA site of N2O reductase and cytochrome-c oxidase.
SourceEur. J. Biochem. 208:31-40(1992).
PubMed ID1324835

5AuthorsSaraste M.
SourceUnpublished observations (1994).

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