| First Author | Christian WV | Year | 2012 |
| Journal | J Biol Chem | Volume | 287 |
| Issue | 25 | Pages | 21233-43 |
| PubMed ID | 22535958 | Mgi Jnum | J:187538 |
| Mgi Id | MGI:5437400 | Doi | 10.1074/jbc.M112.352245 |
| Citation | Christian WV, et al. (2012) beta-Subunit of the Ostalpha-Ostbeta organic solute transporter is required not only for heterodimerization and trafficking but also for function. J Biol Chem 287(25):21233-43 |
| abstractText | The organic solute transporter, Ost/Slc51, is composed of two distinct proteins that must heterodimerize to generate transport activity, but the role of the individual subunits in mediating transport activity is unknown. The present study identified regions in Ostbeta required for heterodimerization with Ostalpha, trafficking of the Ostalpha-Ostbeta complex to the plasma membrane, and bile acid transport activity in HEK293 cells. Bimolecular fluorescence complementation analysis revealed that a 25-amino acid peptide containing the Ostbeta transmembrane (TM) domain heterodimerized with Ostalpha, although the resulting complex failed to reach the plasma membrane and generate cellular [(3)H]taurocholate transport activity. Deletion of the single TM domain of Ostbeta abolished interaction with Ostalpha, demonstrating that the TM segment is necessary and sufficient for formation of a heteromeric complex with Ostalpha. Mutation of the highly conserved tryptophan-asparagine sequence within the TM domain of Ostbeta to alanines did not prevent cell surface trafficking, but abolished transport activity. Removal of the N-terminal 27 amino acids of Ostbeta resulted in a transporter complex that reached the plasma membrane and exhibited transport activity at 30 degrees C. Complete deletion of the C terminus of Ostbeta abolished [(3)H]taurocholate transport activity, but reinsertion of two native arginines immediately C-terminal to the TM domain rescued this defect. These positively charged residues establish the correct N(exo)/C(cyt) topology of the peptide, in accordance with the positive inside rule. Together, the results demonstrate that Ostbeta is required for both proper trafficking of Ostalpha and formation of the functional transport unit, and identify specific residues of Ostbeta critical for these processes. |
