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* Mitochondrial energy transfer proteins signature *
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Different types of substrate carrier  proteins involved in energy transfer are
found in the inner mitochondrial membrane [1,2,3,4]. These are:

 - The ADP,ATP carrier protein (AAC)  (ADP/ATP translocase)  which exports ATP
   into the  cytosol and  imports  ADP  into  the  mitochondrial  matrix.  The
   sequence of AAC has been obtained from various mammalian, plant  and fungal
   species.
 - The  2-oxoglutarate/malate    carrier    protein  (OGCP),  which    exports
   2-oxoglutarate into the cytosol and imports  malate  or  other dicarboxylic
   acids into  the  mitochondrial matrix. This protein plays an important role
   in several  metabolic  processes  such  as  the  malate/aspartate  and  the
   oxoglutarate/isocitrate shuttles.
 - The phosphate carrier protein, which transports  phosphate  groups from the
   cytosol into the mitochondrial matrix.
 - The brown fat uncoupling  protein (UCP) which dissipates  oxidative  energy
   into heat by transporting protons  from  the cytosol into the mitochondrial
   matrix.
 - The  Grave's  disease  carrier protein (GDC), a protein of unknown function
   by IgG in patients with active Grave's disease.
 - Yeast mitochondrial proteins MRS3 and MRS4.  The exact  function  of  these
   proteins is not known. They suppress a mitochondrial splice defect  in  the
   first intron  of  the  COB  gene  and  may  act as carriers, exerting their
   suppressor activity    by   modulating   solute   concentrations   in   the
   mitochondrion.
 - Yeast protein ACR1 [5],  which  seems  essential for  acetyl-CoA synthetase
   activity.
 - Yeast protein PMT1 [6].
 - Yeast protein YMC1 [7].

Two other  proteins  have  been  found  to  belong to this family, yet are not
localized in the mitochondrial inner membrane:

 - Maize    amyloplast   Brittle-1  protein  [8].  This  protein, found in the
   endosperm of kernels, could play a role in amyloplast membrane transport.
 - Candida  boidinii  peroxisomal  membrane  protein  PMP47  [9].  PMP47 is an
   integral membrane  protein  of  the  peroxisome and it may play a role as a
   transporter.

These proteins all seem to be evolutionary related. Structurally, they consist
of three tandem repeats  of  a  domain of approximately  one hundred residues.
Each of  these  domains  contains  two  transmembrane  regions. As a signature
pattern, we selected one of the most conserved regions in the repeated domain,
located just after the first transmembrane region.

-Consensus pattern: P-x-[DE]-x-[LIVAT]-[RK]-x-[LRH]-[LIVMFY]
-Sequences known to belong to this class detected by the pattern: ALL,  except
 for PMP47.
-Other sequence(s) detected in SWISS-PROT: 185.   However,   in    all   these
 proteins, the pattern is found only ONCE while it is found two to three times
 in members of this family.
-Last update: June 1994 / Text revised.

[ 1] Klingenberg M.
     Trends Biochem. Sci. 15:108-112(1990).
[ 2] Walker J.E.
     Curr. Opin. Struct. Biol. 2:519-526(1992).
[ 3] Nelson D.R., Lawson J.E., Klingenberg M., Douglas M.G.
     J. Mol. Biol. 230:1159-1170(1993).
[ 4] Fernandez M., Fernandez E., Rodicio R.
     Mol. Gen. Genet. 242:727-735(1994).
[ 5] Palmieri F.
     FEBS Lett. 346:48-54(1994).
[ 6] Colleaux L., Richard G.-F., Thierry A., Dujon B.
     Yeast 8:325-336(1992).
[ 7] Graf R., Baum B., Braus G.H.
     Yeast 9:301-305(1993).
[ 8] Sullivan T.D., Strelow L.I., Illingworth C.A., Phillips R.L.,
     Nelson O.E. Jr.
     Plant Cell 3:1337-1348(1991).
[ 9] Jank B., Habermann B., Schweyen R.J., Link T.A.
     Trends Biochem. Sci. 18:427-428(1993).