TCDB is operated by the Saier Lab Bioinformatics Group
TCIDNameDomainKingdom/PhylumProtein(s)
*2.A.90.1.1









The STRA6 vitamin A transporter/RBP receptor mediates cellular uptake of Vitamin A (Sun, 2011). Of 668 aas and probably 9 TMSs (Kawaguchi et al. 2015).  Transport is reversible, and is probably mediated by a carrier or group translocation mechanism (Kelly and von Lintig 2015).  Mechanistic features have been discussed (Kawaguchi et al. 2015), and it was concluded that energy-independent facilitated diffusion, from external retinol binding protein (RBP) to internal CRBP-1 or the corresponding CRABP (for retinoic acid) after release of the substrate into the iipid environment of the membrane or an enzyme that forms retinol esters (LRAT) provides the most probable mechanism.

Eukaryota
Metazoa
STRA6 of Bos taurus (ABG81428)
*2.A.90.1.2









Stimulated by retinoic acid gene 6, STRA6 (670 aas; 8-10 TMSs predicted with N- and C-termini outside) (Kawaguchi et al., 2008).  Mechanistic features have been discussed (Kawaguchi et al. 2015), and it was concluded that energy-independent facilitated diffusion, from external holo-retinol binding protein (RBP) to internal CRBP-1 or the corresponding CRABP (for retinoic acid) after release of the substrate into the iipid environment of the membrane or an enzyme that forms retinol esters (LRAT) provides the most probable mechanism.

Eukaryota
Metazoa
STRA6 of Mus musculus (O70491)
*2.A.90.1.3









STRA6 of 667 aas and 9 - 12 putative TMSs (Zhong et al. 2013).  Mechanistic features have been discussed (Kawaguchi et al. 2015), and it was concluded that energy-independent facilitated diffusion, from external holo-retinol binding protein (RBP) to internal CRBP-1 or the corresponding CRABP (for retinoic acid) after release of the substrate into the iipid environment of the membrane or an enzyme that forms retinol esters (LRAT) provides the most probable mechanism of transport.  STRA6 binds RBP with a 1:1 stoichiometry (Breen et al. 2015).

Eukaryota
Metazoa
STRA6 of Homo sapiens
*2.A.90.1.4









STRA6 of 670 aas, mediates cellular uptake of vitamin A by recognizing RBP-retinol to trigger release and internalization of retinol. Chen et al. 2016 presented the structure of zebrafish STRA6, determined to 3.9-angstrom resolution by single-particle cryo-electron microscopy. STRA6 has one intramembrane and nine transmembrane helices in an intricate dimeric assembly. Calmodulin is bound tightly to STRA6 in a noncanonical arrangement. Residues involved with RBP binding map to an arch-like structure that covers a deep lipophilic cleft. This cleft is open to the membrane, suggesting a possible mode for internalization of retinol through direct diffusion into the lipid bilayer.

Eukaryota
Metazoa
STRA6 of Danio rerio (Zebrafish) (Brachydanio rerio)
*2.A.90.2.1









Sea urchin protein of unknown function

Eukaryota
Metazoa
Uncharacterized protein of Strongylocentrotus purpuratus
*2.A.90.2.2









Rotifer Stra6 protein of 655 aas

Eukaryota
Metazoa
Stra6 homologue of Adineta (Callidina) vaga
*2.A.90.2.3









Stra6 homologue of 716 aas

Eukaryota
Ichthyosporea
Stra6 homologue of Capsaspora owczarzaki
*2.A.90.2.4









Stra6 homologue of 1327 aas

Eukaryota
Choanoflagellida
Stra6 homologue of Monosiga brevicollis
*2.A.90.3.1









Harmful bloom algal protein of unknown function, of 962 aas and 16 putative TMSs.  TMSs 1-5 or 6 correspond to synaptic glycoprotein SC2, possibly a sterol reductase (TC@2.A.90.3.2 and3.3), while the last 5 TMSs are homologous to TMSs 7 - 11 in the 11 TMS STRA6 protein (2.A.90.1.1).  Thus, this protein may be a fusion protein.   

Eukaryota
Pelagophyceae
Uncharacterized protein of Aureococcus anophagefferens
*2.A.90.3.2









Synaptic glycoprotein SC2 of 299 aas and 6 TMSs.

Eukaryota
Metazoa
SC2 of Culex quinquefasciatus (Southern house mosquito) (Culex pungens)
*2.A.90.3.3









Putative steroid reductase required for elongation of the very long chain fatty acids, of 285 aas and 6 TMSs.

Eukaryota
Metazoa
Reductase of Ixodes ricinus (Common tick)
*2.A.90.3.4









Steroid 5-alpha reductase, putative, of 252 aas and 6 TMSs.

Eukaryota
Entamoebidae
Reductase of Entamoeba histolytica
*2.A.90.3.5









Uncharacterized protein of 287 aas and 5 or 6 TMSs.

Eukaryota
Entamoebidae
UP of Entamoeba histolytica