The
Transporter-Opsin-G protein-coupled receptor (TOG) Superfamily consists of integral membrane proteins, usually of 7 or 8 transmembrane
alpha-helical segments (TMSs), that share a common evolutionary origin. The designation, the Transporter/Opsin/G protein-coupled receptor (TOG) superfamily, is based on the currently best-characterized families present in this superfamily. In addition to; (1) ion-translocating microbial rhodopsins (MR;
TC# 3.E.1] and (2) G protein-coupled receptors (GPCRs;
TC# 9.A.14], including visual
rhodopsins (VRs), members of the following families share a common origin with microbial, invertebrate and vertebrate rhodopsins: (3) Sweet sugar transporters (Sweet;
TC# 2.A.123], (4) nicotinamide ribonucleoside uptake
permeases (PnuC;
TC# 4.B.1], (5)
4-toluene sulfonate uptake permeases (TSUP;
TC# 2.A.102], (6)
Ni2+–Co2+ transporters (NiCoT;
TC# 2.A.52], (7)
organic solute transporters (OST;
TC# 2.A.82], (8)
phosphate:Na+ symporters (PNaS;
TC# 2.A.58] and (9)
lysosomal cystine transporters (LCT;
TC# 2.A.43].