The transporter-opsin-G protein-coupled receptor (TOG) superfamily is a protein superfamily of integral membrane proteins, usually of 7 or 8 transmembrane alpha-helical segments (TMSs). It includes (1) ion-translocating microbial rhodopsins and (2) G protein-coupled receptors (GPCRs), (3) Sweet sugar transporters, (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).
The gluconate:H+ symporter (GntP) family (TC# 2.A.8) is a family of transport proteins belonging to the ion transporter (IT) superfamily. Members of the GntP family include known gluconate permeases of E. coli and Bacillus species such as the D-Gluconate:H+ symporter of Bacillus subtillus (GntP; TC# 2.A.8.1.1) and the D-fructuronate/D-gluconate:H+ symporter of E. coli (GntP; TC# 2.A.8.1.3). A representative list of proteins belonging to the GntP family can be found in the Transporter Classification Database.
The p-aminobenzoyl-glutamate transporter(AbgT) family is a family of transporter proteins belonging to the ion transporter (IT) superfamily. The AbgT family consists of the AbgT protein of E. coli and the MtrF drug exporter of Neisseria gonorrhoeae. The former protein is apparently cryptic in wild-type cells, but when expressed on a high copy number plasmid, or when expressed at higher levels due to mutation, it appeared to allow uptake and subsequent utilization of p-aminobenzoyl-glutamate as a source of p-aminobenzoate for p-aminobenzoate auxotrophs. p-Aminobenzoate is a constituent of and a precursor for the biosynthesis of folic acid. MtrF was annotated as a putative drug efflux pump.
Phosphate permeases are membrane transport proteins that facilitate the diffusion of phosphate into and out of a cell or organelle. Some of these families include:
The Holin Superfamily I is a superfamily of integral membrane transport proteins. It is one of the seven different holin superfamilies in total. In general, these proteins are thought to play a role in regulated cell death, although functionality varies between families and individual members.
The ion transporter (IT) superfamily is a superfamily of secondary carriers that transport charged substrates.
The Citrate-Mg2+:H+ (CitM) / Citrate-Ca2+:H+ (CitH) Symporter (CitMHS) Family (TC# 2.A.11) is a family of transport proteins belonging to the Ion transporter superfamily. Members of this family are found in Gram-positive and Gram-negative bacteria, archaea and possibly eukaryotes. These proteins all probably arose by an internal gene duplication event. Lensbouer & Doyle (2010) have reviewed these systems, classifying the porters with three superfamilies, according to ion-preference:
Arsenite resistance (Ars) efflux pumps of bacteria may consist of two proteins, ArsB and ArsA, or of one protein. ArsA proteins have two ATP binding domains and probably arose by a tandem gene duplication event. ArsB proteins all possess twelve transmembrane spanners and may also have arisen by a tandem gene duplication event. Structurally, the Ars pumps resemble ABC-type efflux pumps, but there is no significant sequence similarity between the Ars and ABC pumps. When only ArsB is present, the system operates by a pmf-dependent mechanism, and consequently belongs in TC subclass 2.A. When ArsA is also present, ATP hydrolysis drives efflux, and consequently the system belongs in TC subclass 3.A. ArsB therefore appears twice in the TC system but ArsA appears only once. These pumps actively expel both arsenite and antimonite.
The arsenical resistance-3 (ACR3) family is a member of the BART superfamily. Based on operon analyses, ARC3 homologues may function either as secondary carriers or as primary active transporters, similarly to the ArsB and ArsAB families. In the latter case ATP hydrolysis again energizes transport. ARC3 homologues transport the same anions as ArsA/AB homologues, though ArsB homologues are members of the IT Superfamily and homologues of the ARC3 family are within the BART Superfamily suggesting they may not be evolutionarily related.
The Pho1 phosphate permease family is a family of phosphate transporters belonging to the ion transporter (IT) superfamily. Representative members of the Pho1 family include the putative phosphate transporter PHO1 of Arabidopsis thaliana, and the xenotropic and polytropic murine-leukemia virus receptor Xpr1 of Culex pipiens.
The Malonate Uptake (MatC) family is a constituent of the ion transporter (IT) superfamily. It consists of proteins from Gram-negative and Gram-positive bacteria, simple eukaryotes and archaea. The proteins are of about 450 amino acyl residues in length with 12-14 putative transmembrane segments (TMSs). Closest functionally-characterized homologues are in the DASS family. One member of this family is a putative malonate transporter.
The Basic Amino Acid Antiporter (ArcD) family is a constituent of the IT superfamily. This family consists of proteins from Gram-negative and Gram-positive bacteria. The proteins are of about 480 amino acyl residues (aas) in length and have 10-12 putative transmembrane segments (TMSs). Functionally characterized homologues are in the DcuC and ArsB families. Some members of the family probably catalyze arginine/ornithine or citrulline/ornithine antiport.
The NhaB family belongs to the ion transporter (IT) superfamily. A representative list of proteins belonging to the NhaB family can be found in the Transporter Classification Database.
The NhaE family belongs to the Ion Transporter (IT) Superfamily which has an end. A representative list of proteins belonging to the NhaE family can be found in the Transporter Classification Database.
The inorganic phosphate transporter (PiT) family is a group of carrier proteins derived from Gram-negative and Gram-positive bacteria, archaea, and eukaryotes.
The Deinococcus/Thermus Holin (D/T-Hol) Family consists of a single protein with no close homologues ; however, its distant homology to members of the Holin superfamily III suggest an evolutionary relationship. The putative holin of Meiothermus silvanus is 108 amino acyl residues in length and possesses 3 transmembrane segments.
The Holin superfamily V is a superfamily of integral membrane transport proteins. It is one of the seven different holin superfamilies in total. In general, these proteins are thought to play a role in regulated cell death, although functionality varies between families and individual members. The Holin superfamily V includes the TC families:
The Holin superfamily VI is a superfamily of integral membrane transport proteins. It is one of the seven different holin superfamilies in total. In general, these proteins are thought to play a role in regulated cell death, although functionality varies between families and individual members.
The Holin superfamily VII is a superfamily of integral membrane transport proteins. It is one of the seven different holin superfamilies in total. In general, these proteins are thought to play a role in regulated cell death, although functionality varies between families and individual members.
The Putative 3-4 TMS Transglycosylase-associated Holin Family is believed to be a group of holins that does not belong to one of the seven holin superfamilies. Homologues include thousands of diverse phage and bacterial proteins between 80 and 140 amino acyl residues (aas) in length that exhibit 3 to 4 transmembrane segments (TMSs). These proteins are holin-like in their size and topology and are designated 'Transglycosylase-associated', 'Putative holin', 'Phage-like transmembrane protein', 'YeaQ protein', etc. in the NCBI protein database. As of early 2016, they remain functionally uncharacterized. They derive from a wide range of bacterial and archaeal phyla including both Gram-negative and Gram-positive bacteria. These proteins are related to the RDD family in the conserved domain database. A representative list of proteins belonging to the T-A Hol family can be found in the Transporter Classification Database.
