{PDOC00767}
{PS01000; SDH_CYT_1}
{PS01001; SDH_CYT_2}
{BEGIN}
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* Succinate dehydrogenase cytochrome b subunit signatures *
***********************************************************

Succinate dehydrogenase   (SDH)  is  a  membrane-bound  complex  of  two  main
components: a   membrane-extrinsic   component   composed   of  an FAD-binding
flavoprotein and an iron-sulfur protein, and a hydrophobic  component composed
of a cytochrome B and a membrane anchor protein. The cytochrome b component is
a mono heme transmembrane protein [1,2,3] belonging to a family that groups:

 - Cytochrome b-556 from bacterial SDH (gene sdhC).
 - Cytochrome b560 from the mammalian mitochondrial SDH complex.
 - Cytochrome b560 subunit encoded in the mitochondrial genome of some algae
   and in the plant Marchantia polymorpha.
 - Cytochrome b from yeast mitochondrial SDH complex (gene SDH3 or CYB3).
 - Protein cyt-1 from Caenorhabditis.

These cytochromes  are  proteins  of  about  130  residues that comprise three
transmembrane regions.  There  are  two  conserved  histidines  which  may  be
involved in  binding  the heme group. We developed two signature patterns that
include these histidine residues.

-Consensus pattern: R-P-[LIVMT]-x(3)-[LIVM]-x(6)-[LIVMWPK]-x(4)-S-x(2)-H-R-x-
                    [ST]
                    [H may be a heme ligand]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Consensus pattern: H-x(3)-[GA]-[LIVMT]-R-[HF]-[LIVMF]-x-[FYWM]-D-x-[GVA]
                    [H may be a heme ligand]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Note: The di-heme cytochrome b-558 from Bacillus subtilis  SDH complex is not
 a member of this family.

-Last update: May 2004 / Text revised.

[ 1] Yu L., Wei Y.-Y., Usui S., Yu C.-A.
     "Cytochrome b560 (QPs1) of mitochondrial succinate-ubiquinone
     reductase. Immunochemistry, cloning, and nucleotide sequencing."
     J. Biol. Chem. 267:24508-24515(1992).
     PubMed=1447196
[ 2] Abraham P.R., Mulder A., van 't Riet J., Raue H.A.
     "Characterization of the Saccharomyces cerevisiae nuclear gene CYB3
     encoding a cytochrome b polypeptide of respiratory complex II."
     Mol. Gen. Genet. 242:708-716(1994).
     PubMed=8152421
[ 3] Leblanc C., Boyen C., Richard O., Bonnard G., Grienenberger J.M.,
     Kloareg B.
     "Complete sequence of the mitochondrial DNA of the rhodophyte Chondrus
     crispus (Gigartinales). Gene content and genome organization."
     J. Mol. Biol. 250:484-495(1995).
     PubMed=7616569

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