TCDB is operated by the Saier Lab Bioinformatics Group
TCIDNameDomainKingdom/PhylumProtein(s)
2.A.94.1.1









Putative phosphate transporter, Pho1 (one of ten paralogues) (782 aas; 10 or 11 TMSs) (Hamburger et al., 2002)

Eukaryota
Viridiplantae, Streptophyta
Pho1 of Arabidopsis thaliana (Q8S403)
2.A.94.1.2









Xenotropic and polytropic murine-leukemia virus receptor Xpr1 of 671 aas and 11 or 12 TMSs. XPR1 senses intracellular Pi levels via its SPX domain and downregulates cellular Pi uptake via the C-terminal domain; it may not be a transporter (Burns et al. 2024).

Eukaryota
Metazoa, Arthropoda
Xpr1 of Culex pipiens (XP_001850310)
2.A.94.1.3









Pho1 homologue of 396 aas and probably either 10 or 11 TMSs, ERD1.

Eukaryota
Fungi, Ascomycota
ERD1 of Cercospora beticola
2.A.94.1.4









EXS-domain-containing protein of 565 aas and probably 10 or 11 TMSs.

Eukaryota
Fungi, Mucoromycota
EXS protein of Mortierella elongata
2.A.94.1.5









EXS family protein of 414 aas and 8 - 11 TMSs.

Eukaryota
Ciliophora
EXS protein of Tetrahymena thermophila
2.A.94.1.6









The Xenotropic and polytropic retrovirus receptor 1, the XPR1 or SLC53A1 protein, also called SYG1 or XR of 696 aas and 10 - 12 TMSs. XPR1 exports inorganic phosphate in metazoans (Giovannini et al. 2013) and is associated with Primary Familial Brain Calcification (PFBC, formerly known as Fahr disease or Idiopathic Basal Ganglia Calcification in idiopathic forms) (Legati et al. 2015 and Anheim et al. 2016). It binds inositol hexakisphosphate (Ins6P) and similar inositol polyphosphates, such as 5-diphospho-inositol pentakisphosphate (5-InsP7), important intracellular signaling molecules (Wild et al. 2016). It has been associated with Primary Familial Brain Calcification (PFBC) (Monfrini et al. 2023).  XPR1 senses intracellular Pi levels via its SPX domain and downregulates cellular Pi uptake via the C-terminal domain; it may not be a transporter (Burns et al. 2024).  However, Zhang et al. 2025 provided structural insights into the mechanism of phosphate recognition and transport by XPR1.

Eukaryota
Metazoa, Chordata
XPR1 of Homo sapiens
2.A.94.1.7









Erd1 of 362 aas, possibly with 7 TMSs in a 1 + 2 + 3 + 1 TMS arrangement, where the first 3 TMSs are stronly hydrophobic, but the last 4 are only moderately hydrophobic. It is required for the retention of luminal endoplasmic reticulum/Golgi proteins and affects glycoprotein processing in the Golgi apparatus. Protein glycosylation in the Golgi is a sequential process that requires proper distribution of transmembrane glycosyltransferase enzymes in the appropriate Golgi compartments. Some of the cytosolic machinery required for the steady-state localization of some Golgi enzymes are known. Erd1 facilitates Golgi glycosyltransferase recycling by directly interacting with both the Golgi enzymes and the cytosolic receptor, Vps74 (Sardana et al. 2021). Loss of Erd1 function results in mislocalization of Golgi enzymes to the vacuole/lysosome. Erd1 forms an integral part of the recycling machinery while ensuring productive recycling of several early Golgi enzymes. It also determines how the localization of Golgi glycosyltransferases is spatially and temporally regulated (Sardana et al. 2021).

 

Eukaryota
Fungi, Ascomycota
Erd1 of Saccharomyces cerevisiae