TCDB is operated by the Saier Lab Bioinformatics Group
TCIDNameDomainKingdom/PhylumProtein(s)
2.A.43.1.1









Lysosomal cystine transporter, cystinosin (CTNS) of 267 aas and 7 TMSs. It uses a cystine:H+ symport mechanism. H+ binds to an aspartate residue in one of the two PQ-loops (Ruivo et al., 2012). Several mutations in the CTNS gene gives rise to ocular cystinosis (Browning et al. 2019). Microvesicle delivery of cystinosin to ex vivo corneal keratocytes (corneal fibroblasts) corrects the cystine transport defect and prevents the accumulation of lysosomal cystine (Thoene et al. 2020). Impaired transport of cystine out of lysosomes is associated with mutations in transmembrane domains of cystinosin, resulting from loss of its activity (Chkioua et al. 2022). Cystinosis is characterized by early-onset chronic kidney failure and progressive development of extra-renal complications (Taranta et al. 2021).

Eukaryota
Metazoa, Chordata
Cystinosin or CTNS of Homo sapiens
2.A.43.1.2









Cystinosin homolog
Eukaryota
Metazoa, Arthropoda
CG17119 of Drosophila melanogaster
2.A.43.1.3









The ERD-1 suppressor, ERS1

Eukaryota
Fungi, Ascomycota
ERS1 of Saccharomyces cerevisiae (P17261)
2.A.43.1.4









Cystinosin homolog of 270 aas and 6 or 7 TMSs uses the proton gradient to drive cystine export from the lysosome into the cytoplasm. Löbel et al. 2022 presented the crystal structures of cystinosin from Arabidopsis thaliana in both apo and cystine bound states. They establish a mechanism for cystine recognition and proton coupled transport. Mutational mapping and functional characterisation of human cystinosin provided a framework for understanding the molecular impact of disease-causing mutations.

Eukaryota
Viridiplantae, Streptophyta
At5g40670 of Arabidopsis thaliana
2.A.43.1.6









Cystinosin of 355 aas and 7 TMSs.

Eukaryota
Evosea
Cystinosin of Planoprotostelium fungivorum
2.A.43.2.1









The lysosomal lysine-arginine transporter, LAAT1, SLC66A1, PQ-loop repeat containing protein 2 (PQLC2) (291 aas; 7 TMSs). Also transports L-histidine, L-ornithine, the mixed disulfide of cysteine-cysteamine, a lysine analogue, as well as canavanine, a toxic arginine analogue. Cysteamine is used in the treatment of cystinosis (Liu et al., 2012; Jézégou et al. 2012).

Eukaryota
Metazoa, Chordata
PQLC2 of Homo sapiens (Q6ZP29)
2.A.43.2.2









The lysosomal lysine-arginine transporter, LAAT1, PQ-loop superfamily member (qx42 gene product; 310aas; 7 TMSs) (Liu et al., 2012).

Eukaryota
Metazoa, Nematoda
LAAT1 of Caenorhabditis elegans (Q95XZ6)
2.A.43.2.3









Vacuolar (lysosomal) cationic amino acid transporter (YOL092W) (308aas; 7 TMSs), LAAT1.  Involved in cationic amino acid homeostasis (Jézégou et al. 2012). It may function as an amino acid exporter of cationic amino acids from the vacuole. The vacuole-associated Rsp5 ubiquitin ligase uses a TMS in the substrate adaptor Ssh4 to recognize membrane helices in Ypq1, which targets this lysine transporter for lysosomal degradation during lysine starvation (Zhang and Ye 2021).

 

Eukaryota
Fungi, Ascomycota
LAAT1 of Saccharomyces cerevisiae (Q12010)
2.A.43.2.4









PQ-loop repeat protein (320aas; 7 TMSs)

Eukaryota
Evosea
PQLR protein Entamoeba histolyticus (C4LT11)
2.A.43.2.5









PQ-loop repeat protein (288aas; 7 TMSs)

Eukaryota
Viridiplantae, Streptophyta
 PQLR protein of Arabidopsis thaliana (O49437)
2.A.43.2.6









7 TMS protein 1 (319aas; 7 TMSs)

Eukaryota
Fornicata
7 TMS protein of Giardia lamblia (E1F7I8)
2.A.43.2.7









Probable vacuolar (lysosomal) cationic amino acid exporter, RTC2 (Ypq3; Ybr147). Involved in amino acid homeostasis. Up-regulated by addition of ammonia or amino acids to a nitrogen-depleted medium (Jézégou et al. 2012). Resistant to fluconazole. Increased resistance to caspofungin. Suppresses CDC13-1 temperature sensitivity.

Eukaryota
Fungi, Ascomycota
RTC2 of Saccharomyces cerevisiae
2.A.43.2.8









Vacuolar (lysosomal) putative cationic amino acid exporter, Ypq2 (Ydr352); involved with cationic amino acid homeostasis (Jézégou et al. 2012).

Eukaryota
Fungi, Ascomycota
Ypq2 of Saccharomyces cerevisiae
2.A.43.2.9









PQ loop protein of 384 aas and 7 (3 + 4) TMSs

Eukaryota
Viridiplantae, Streptophyta
PQ-loop protein of Populus trichcarpa
2.A.43.2.10









The probable vacuolar amino acid transporter YPQ1 of 381 aas and 6 TMSs.

Eukaryota
Viridiplantae, Streptophyta
Ypq1 of Sesamum indicum
2.A.43.2.11









The probable vacuolar amino acid transporter Ypq1 of 381 aas and 6 TMSs

Eukaryota
Viridiplantae, Streptophyta
Ypq1 of Gossypium raimondii].
2.A.43.2.12









Uncharacterized protein of 282 aas and 7 (3 + 4) TMSs.

Eukaryota
Viridiplantae, Streptophyta
UP of Gossypium raimondii
2.A.43.2.13









Cdc50 supressor, CSF1 of 405 aas and 7 TMSs.  Appears to function as a phospholipid flippase or to regulate PL flipping in endosomes or late golgi vesicles (Yamamoto et al. 2017).

Eukaryota
Fungi, Ascomycota
CSF1 of Saccharomyces cerevisiae
2.A.43.2.14









Uncharacterized PQ loop repeat protein of 228 aas and 6 TMSs.

Eukaryota
Evosea
UP of Entamoeba histolytica
2.A.43.2.15









PQ loop C1 (PQLC1; SLC66A2) protein of 271 aas and 7 TMSs in a 3 + 4 TMS arrangement. It probably transports a variety of amino acids and their derivatives as does PQLC2 (TC# 2.A.43.2.1).

Eukaryota
Metazoa, Chordata
PQLC2 of Homo sapiens
2.A.43.2.16









PQLC2L or SLC66A11L or 304 aas and 7 TMSs. 

Eukaryota
Metazoa, Chordata
PQLC2L of Gallus gallus (chicken)
2.A.43.3.1









The Lec15/Lec35 suppressor, SL15, MPDU1 or SLC66A5, of 247 aas and probably 7 TMSs. It is a suppressor of the Lec15 and Lec35 glycosylation mutations (Ware and Lehrman 1998). The human ortholog is 89% identical to this protein. This protein may be required for normal utilization of mannose-dolichol phosphate (Dol-P-Man) in the synthesis of N-linked and O-linked oligosaccharides and GPI anchors.

Eukaryota
Metazoa, Chordata
SL15 of Cricetulus griseus
2.A.43.3.2









PQ-loop-containing protein 3 (PQLC3) of 202 aas and 7 closely spaced TMSs. It may play a role in gestational diabetes mellitus (Li et al. 2021). It may also function in tumor mutation burden for predicting lymph node metastasis in breast cancer (Wang et al. 2021).

Eukaryota
Metazoa, Chordata
PQLC3 of Mus musculus (Q8C6U2)
2.A.43.4.1









Uncharacterized protein C4C5.03
Eukaryota
Fungi, Ascomycota
SPAC4C5.03 of Schizosaccharomyces pombe
2.A.43.4.2









Uncharacteerized protein of 308 aas and 7 TMSs.

Eukaryota
Evosea
UP of Entamoeba histolytica
2.A.43.4.3









Uncharacterized protein of 363 aas and 8 TMSs.

Eukaryota
Evosea
UP of Entamoeba histolytica
2.A.43.5.1









Transmembrane protein 44, TMEM44, of 475 aas and 7 TMSs in a 1 + 2 + 2 + 2 TMS arrangement. TMEM44, as a novel prognostic marker for kidney renal clear cell carcinoma, is associated with tumor invasion, migration and immune infiltration (Tian et al. 2023).

Eukaryota
Metazoa, Chordata
TMEM44 of Homo sapiens
2.A.43.5.2









Uncharacterized protein of 358 aas and 5 N-terminal TMSs. 

Eukaryota
Metazoa, Chordata
UP of Austrofundulus limnaeus
2.A.43.5.3









TMEM44 isoform X5 of 360 aas and 7 TMSs in a 1 + 5 + 1  TMS arrangement.

Eukaryota
Metazoa, Chordata
TMEM44 of Gadus chalcogrammus (walleye pollock)
2.A.43.5.4









TMEM44 Isooform 5 of 378 aas and 4 - 6 N-terminal TMSs.

Eukaryota
Metazoa, Chordata
TMEM44 of Pseudochaenichthys georgianus (South Georgia icefish)
2.A.43.5.5









TMEM43 isoform X6 of 399 aas and 7 TMSs in a 4 + 3 arrangement near the N-terminus of the protein.

Eukaryota
Metazoa, Chordata
TMEM43 of Doryrhamphus excisus (bluestripe pipefish)
2.A.43.5.6









Uncharacterized protein isoform X1 of 543 aas and 7 TMSs in a 3 + 1 + 3 TMS arrangement.

Eukaryota
Metazoa, Echinodermata
UP of Acanthaster planci (crown-of-thorns starfish)