The most recent families added include the PAAP (Putative Amino Acid Permease), LIVCS (Branched Chain Amino Acid:Cation Symporter), NRAMP (Natural Resistance-Associated Macrophage Protein), CstA (Carbon starvation A protein), KUP (K+ Uptake Permease), BenE (Benzoate:H+ Virginia Symporter), and AE (Anion Exchanger).
All new entries contain the two 5 or 7 TMS repeat units characteristic of the APC superfamily, sometimes with extra TMSs at the ends likely the result of an addition prior to duplication.
New functionally characterized members transport amino acids, peptides, and inorganic anions or cations.
In CadB of E. coli (2.A.3.2.2), amino acid residues involved in both uptake and excretion, or solely in excretion are located in the cytoplasmic loops and the cytoplasmic side of transmembrane segments, whereas residues involved in uptake are located in the periplasmic loops and the transmembrane segments.
[8] A hydrophilic cavity is proposed to be formed by the transmembrane segments II, III, IV, VI, VII, X, XI, and XII.
[8] Based on 3-D structures of APC superfamily members, Rudnick (2011) has proposed the pathway for transport and suggested a "rocking bundle" mechanism.
The central cavity of CadB, containing the substrate-binding site is wider than that of PotE, mirroring the different sizes of cadaverine and putrescine.
AdiC mirrors the common fold observed unexpectedly in four phylogenetically unrelated families of Na+-coupled solute transporters: BCCT (2.A.15), NCS1 (2.A.39), SSS (2.A.21) and NSS (2.A.22).