Family 2.A.3 - The Amino Acid-Polyamine-Organocation Superfamily
Family ID: 52614
The APC superfamily of transport proteins includes members that
function as solute:cation symporters and solute:solute antiporters.
They occur in bacteria, archaea, yeast, fungi, unicellular eukaryotic
protists, slime molds, plants and animals. They vary in length,
being as small as 350 residues and as large as 850 residues. The
smaller proteins are generally of prokaryotic origin while the
larger ones are of eukaryotic origin. Most of them possess twelve
transmembrane a-helical spanners, but members of one family within
the APC superfamily (SGP; TC# 2.A.3.9) have 10 TMSs, while the
eukaryotic members of another family (CAT; TC# 2.A.3.3) have 14
TMSs. The larger eukaryotic and archael proteins possess N- and
C-terminal hydrophilic extensions. Some animal proteins, for example,
those in the LAT family (TC# 2.A.3.8) including ASUR4 (gbY12716)
and SPRM1 (gbL25068) associate with a type 1 transmembrane glycoprotein
that is essential for insertion or activity of the permease and
forms a disulfide bridge with it. These glycoproteins include
the CD98 heavy chain protein of Mus musculus (gbU25708) and the
4F2 cell surface antigen heavy chain of Homo sapiens (spP08195).
They are members of the rBAT family of mammalian proteins (TC
#8.A.9). One APC family member, Hip1 of S. cerevisiae (TC #2.A.3.1.5),
has been implicated in heavy metal transport. Distant constituents
of the APC superfamily are the AAAP family (TC# 2.A.18), the ArAAP
family (TC# 2.A.42) and the STP family (TC# 2.A.43). Some of these
proteins exhibit 11 TMSs.
