{PDOC00554}
{PS00641; COMPLEX1_75K_1}
{PS00642; COMPLEX1_75K_2}
{PS00643; COMPLEX1_75K_3}
{BEGIN}
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* Respiratory-chain NADH dehydrogenase 75 Kd subunit signatures *
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Respiratory-chain NADH dehydrogenase (EC 1.6.5.3) [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  75 Kd (in mammals),  which is the
largest subunit  of complex I  and  is  a  component  of  the iron-sulfur (IP)
fragment of the enzyme.  It  seems  to bind to two 4Fe-4S clusters (called N-3
and N-4).

The 75 Kd subunit is highly similar to [3,4]:

 - Subunit gamma of Alcaligenes eutrophus NAD-reducing hydrogenase (gene hoxU)
   which also binds two 4Fe-4S cluster.
 - Subunit NQO3 of Paracoccus denitrificans NADH-ubiquinone oxidoreductase.
 - Subunit G of Escherichia coli NADH-ubiquinone oxidoreductase (gene nuoG).

The 75 Kd subunit and the bacterial  hydrogenase  gamma subunit contains three
conserved clusters of  cysteine  residues  which are most probably involved in
the binding of the iron-sulfur clusters.  We have developed signature patterns
for these three regions.

-Consensus pattern: P-x(2)-C-[YWSD]-x(7)-[GA]-x-C-R-x-C
                    [The 3 C's may be 4Fe-4S ligands]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Consensus pattern: C-P-x-C-[DE]-x-[GS](2)-x-C-x-L-Q
                    [The 3 C's may be 4Fe-4S ligands]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Consensus pattern: R-C-[LIVM]-x-C-x-R-C-[LIVMT]-x-[LMFY]
                    [The 3 C's may be 4Fe-4S ligands]
-Sequences known to belong to this class detected by the pattern: ALL,  except
 for NQO3 and nuoG.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Last update: December 2004 / Pattern and text revised.

[ 1] Ragan C.I.
     Curr. Top. Bioenerg. 15:1-36(1987).
[ 2] Weiss H., Friedrich T., Hofhaus G., Preis D.
     "The respiratory-chain NADH dehydrogenase (complex I) of
     mitochondria."
     Eur. J. Biochem. 197:563-576(1991).
     PubMed=2029890
[ 3] Fearnley I.M., Walker J.E.
     "Conservation of sequences of subunits of mitochondrial complex I and
     their relationships with other proteins."
     Biochim. Biophys. Acta 1140:105-134(1992).
     PubMed=1445936
[ 4] Weidner U., Geier S., Ptock A., Friedrich T., Leif H., Weiss H.
     "The 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."
     J. Mol. Biol. 233:109-122(1993).
     PubMed=7690854

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