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The organic solute transporter, OSTα/OSTβ, which transports steroids and other organic solutes including taurocholate, estrone sulfate, digoxin, and prostaglandin E2 (Wang et al. 2001). Transport is sodium-independent, saturable, and inhibited by other steroids and anionic drugs. Human and mouse OSTalpha-OSTbeta were able to mediate transport of taurocholate, digoxin, and prostaglandin E2 but not of estradiol 17beta-d-glucuronide or p-aminohippurate (Seward et al. 2003).

Metazoa, Chordata
OSTα/OSTβ of the little skate, Raja erinacea
OSTα (AAK14805)
OSTβ (AAK14806)

The organic solute transporter OSTα/OSTβ or SLC51A/SLC51B (transports the same anions as the 2.A.82.1.1 system) (The ileal enterocyte basolateral bile acid transporter; uses facilitated diffusion vian an anion:anion antiport mechanism with sulfate or bicarbonate as the counter anion) (Dawson et al., 2005).  Transports steroid-derived molecules as well as glycine and taurine conjugated bile acids (Ballatori et al. 2013).  Heterodimerization increases stability, facilitates post-translational modification and is required for delivery to the plasma membrane.  This system is essential for intestinal bile acid and dietary lipid absorption (Ballatori et al. 2013). Four OSTalpha amino acids (Ser228, Thr229, Gln269 and Glu305) affect expression of OSTalpha/beta and may influence OSTalpha/beta-mediated bile acid transport (Murphy et al. 2021).

Metazoa, Chordata
OSTα/OSTβ of Homo sapiens
OSTα (AAP23993)
OSTβ (AAP23992)

Transmembrane protein 184B (Putative MAPK-activating protein FM08).  It has been concluded that this protein is responsible for ibuprofin and possibly taurine uptake, and that its gene expression is regulated by the Nfat5 transcription factor (Rasmussen et al. 2019).

Metazoa, Chordata
TMEM184B of Homo sapiens

Organic solute transporter alpha-like protein C18A3.4
Metazoa, Nematoda
C18A3.4 of Caenorhabditis elegans

Ostα subunit homologue

Ostα of Thalassiosira oceanica

Uncharacterized protein of 335 aas and 7 TMSs.

Metazoa, Chordata
UP of Oreochromis niloticus (Nile tilapia) (Tilapia nilotica)

Uncharacteerized protein of 356 aas and 8 TMSs.

UP of Entamoeba histolytica

Transmembrane protein 184 (TMM184) homolog of 426 aas and 6 TMSs.

Fungi, Ascomycota
TMM184 of Schizosaccharomyces pombe (Fission yeast)

TMEM184A of 413 aas and 7 TMSs. Heparin decreases the tumor necrosis factor alpha (TNFalpha)-induced endothelial stress responses in vascular smooth muscle cells, and these responses require transmembrane protein 184A as well as induction of dual specificity phosphatase 1 (Farwell et al. 2016). Thus, TMEM184A functions as a heparin receptor and mediates anti-inflammatory responses.

Metazoa, Chordata
TMEM184A of Homo sapiens

Sdmg1 (TMEM184a) of 425 aas and 7 or 8 TMSs in a 3 or 4 + 4 TMS arrangement. Sdmg1 is a component of secretory granules in mouse secretory exocrine tissues. It is mainly expressed in the gonads where it may have a role in mediating signaling between somatic cells and germ cells. Secretory exocrine cells in the pancreas, salivary gland, and mammary gland also have Sdmg1. Expression is up-regulated during pancreas development when regulated secretory granules start to appear, and Sdmg1 colocalizes with secretory granule markers in adult pancreatic acinar cells. It co-purifies with secretory granules during subcellular fractionation of the pancreas, but Sdmg1 and the secretory granule marker Vamp2 are localized to distinct subdomains in the secretory granule membrane. Thus, Sdmg1 is a component of regulated secretory granules in exocrine secretory cells and the developmental regulation of Sdmg1 expression is related to post-Golgi membrane trafficking (Best and Adams 2009). It is associated with germ cell sex determination and germline-soma interactions in mice (Best et al. 2008).

Metazoa, Chordata
Sdmg1 of Mus musculus

Lazarus 1 (ZmLAZ1-4) of 404 aas and 7 TMSs. This zinc uptake transporter modulates zinc homeostasis and can be found on plasma and vacuolar membranes in maize (Liu et al. 2022). In plants, it is a Zn2+ transporter in spite of the dissimilar functions of its homologs in animals (Liu et al. 2022).

Viridiplantae, Streptophyta
LAZ1-4 of Zea mays (Maize)