STRA6
Domain
Contrary to predictions, contains nine transmembrane helices, with an extracellular N-terminus and a cytoplasmic C-terminus (By similarity). Besides, contains one long helix that dips into the membrane and then runs more or less parallel to the membrane surface (By similarity).
Function
Functions as a retinol transporter. Accepts all-trans retinol from the extracellular retinol-binding protein RBP4, facilitates retinol transport across the cell membrane, and then transfers retinol to the cytoplasmic retinol-binding protein RBP1 (PubMed:18316031, PubMed:22665496, PubMed:9452451). Retinol uptake is enhanced by LRAT, an enzyme that converts retinol to all-trans retinyl esters, the storage forms of vitamin A (PubMed:18316031, PubMed:22665496). Contributes to the activation of a signaling cascade that depends on retinol transport and LRAT-dependent generation of retinol metabolites that then trigger activation of JAK2 and its target STAT5, and ultimately increase the expression of SOCS3 and inhibit cellular responses to insulin (PubMed:21368206, PubMed:22665496). Important for the homeostasis of vitamin A and its derivatives, such as retinoic acid (PubMed:18316031). STRA6-mediated transport is particularly important in the eye, and under conditions of dietary vitamin A deficiency (Probable). Does not transport retinoic acid (PubMed:18316031).
Involvement in disease
Microphthalmia, syndromic, 9
MCOPS9
A rare clinical entity including as main characteristics anophthalmia or severe microphthalmia, and pulmonary hypoplasia or aplasia. Microphthalmia is a disorder of eye formation, ranging from small size of a single eye to complete bilateral absence of ocular tissues (anophthalmia). In many cases, microphthalmia/anophthalmia occurs in association with syndromes that include non-ocular abnormalities.
None
The disease is caused by variants affecting the gene represented in this entry.
Mutations in STRA6 may be a cause of isolated colobomatous microphthalmia, a disorder of the eye characterized by an abnormally small ocular globe.
Post-translational modifications
Phosphorylated on tyrosine residues in response to RBP4 binding (PubMed:21368206, PubMed:22665496). Phosphorylation requires the presence of LRAT, suggesting it may be triggered by the uptake of retinol that is then metabolized within the cell to retinoids that function as signaling molecules (PubMed:22665496).
Tissue Specificity
Broad expression. In adult eye expressed in sclera, retina, retinal pigment epithelium, and trabecular meshwork but not in choroid and iris.
Cellular localization
- Cell membrane
- Multi-pass membrane protein
- In the retinal pigment epithelium localizes to the basolateral membrane.
Alternative names
PP14296, UNQ3126/PRO10282/PRO19578, STRA6, Receptor for retinol uptake STRA6, Retinol-binding protein receptor STRA6, Stimulated by retinoic acid gene 6 protein homolog