Family 2.A.29 - The Mitochondrial Carrier Family
Family ID: 52628
Permease protein subunits of the MC family possess six transmembrane
a-helical spanners. The proteins are of fairly uniform size of
about 300 residues. They arose by tandem intragenic triplication
events in which a genetic element encoding two spanners gave rise
to one encoding six spanners. This event may have occurred less
than 1.5 billion years ago when mitochondria first developed their
specialized endosymbiotic functions within eukaryotic cells. Members
of the family are found exclusively in eukaryotic organelles although
they are nuclearly encoded. Most are found in mitochondria, but
some are found in peroxisomes of animals and in amyloplasts of
plants. Structurally characterized members of the MC family are
dimers. Many of them preferentially catalyze the exchange of one
solute for another (antiport). Fifteen paralogues of the MC family
are encoded within the genome of Saccharomyces cerevisiae.
One of the MC family members, the uncoupling protein, UCP1 (TC#
2.A.29.3.1), functions to dissipate the proton motive force, thereby
generating heat. This protein has been shown to be capable of
transporting fatty acids, long chain alkylsulfonates and chloride.
It is believed to allow transport of protons down their electrochemical
gradient in a cyclic, fatty acid-dependent process by first exporting
fatty acyl anions and then allow the free diffusion of the protonated
fatty acid across the bilayer into the mitochondrion. UNC1 is
therfore probably an anion translocator that may not require that
transport occurs by an antiport mechanism. The fatty acid behaves
as a cycling protonophore (Garlid et al, 2000). UNC1 uses coenzyme
Q (ubiquinone) as a cofactor (Echtay et al, 2000). Like many other
MC family members, uncoupling proteins are found in the mitochondria
of plants as well as animals.
