PROSITE documentation PDOC00858
Respiratory-chain NADH dehydrogenase 20 Kd subunit signature


Respiratory-chain NADH dehydrogenase (EC [1,2] (also known as complex I or NADH-ubiquinone oxidoreductase) is an oligomeric enzymatic complex located in the inner mitochondrial membrane which also seems to exist in the chloroplast and in cyanobacteria (as a NADH-plastoquinone oxidoreductase). Among the 25 to 30 polypeptide subunits of this bioenergetic enzyme complex there is one with a molecular weight of 20 Kd (in mammals) [3], which is a component of the iron-sulfur (IP) fragment of the enzyme. It seems to bind a 4Fe-4S iron-sulfur cluster. The 20 Kd subunit has been found to be:

  • Nuclear encoded, as a precursor form with a transit peptide in mammals, and in Neurospora crassa.
  • Mitochondrial encoded in Paramecium (gene psbG).
  • Chloroplast encoded in various higher plants (gene ndhK or psbG).

The 20 Kd subunit is highly similar to [4]:

  • Synechocystis strain PCC 6803 proteins psbG1 and psbG2.
  • Subunit B of Escherichia coli NADH-ubiquinone oxidoreductase (gene nuoB).
  • Subunit NQO6 of Paracoccus denitrificans NADH-ubiquinone oxidoreductase.
  • Subunit 7 of Escherichia coli formate hydrogenlyase (gene hycG).
  • Subunit I of Escherichia coli hydrogenase-4 (gene hyfI).

As as signature pattern we selected a highly conserved region, located in the central section of this subunit and which contains a conserved cysteine that is probably involved in the binding of the 4Fe-4S center.

Last update:

December 2004 / Pattern and text revised.


Technical section

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

COMPLEX1_20K, PS01150; Respiratory-chain NADH dehydrogenase 20 Kd subunit signature  (PATTERN)


1AuthorsRagan C.I.
SourceCurr. Top. Bioenerg. 15:1-36(1987).

2AuthorsWeiss H. Friedrich T. Hofhaus G. Preis D.
TitleThe respiratory-chain NADH dehydrogenase (complex I) of mitochondria.
SourceEur. J. Biochem. 197:563-576(1991).
PubMed ID2029890

3AuthorsArizmendi J.M. Runswick M.J. Skehel J.M. Walker J.E.
TitleNADH: ubiquinone oxidoreductase from bovine heart mitochondria. A fourth nuclear encoded subunit with a homologue encoded in chloroplast genomes.
SourceFEBS Lett. 301:237-242(1992).
PubMed ID1577158

4AuthorsWeidner U. Geier S. Ptock A. Friedrich T. Leif H. Weiss H.
TitleThe gene locus of the proton-translocating NADH: ubiquinone oxidoreductase in Escherichia coli. Organization of the 14 genes and relationship between the derived proteins and subunits of mitochondrial complex I.
SourceJ. Mol. Biol. 233:109-122(1993).
PubMed ID7690854

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