PT  - JOURNAL ARTICLE
AU  - Emanuel Hänggi
AU  - Anne Freimoser Grundschober
AU  - Simone Leuthold
AU  - Peter J. Meier
AU  - Marie V. St-Pierre
TI  - Functional Analysis of the Extracellular Cysteine Residues in the Human Organic Anion Transporting Polypeptide, OATP2B1
AID  - 10.1124/mol.105.019547
DP  - 2006 Sep 01
TA  - Molecular Pharmacology
PG  - 806--817
VI  - 70
IP  - 3
4099  - http://molpharm.aspetjournals.org/content/70/3/806.short
4100  - http://molpharm.aspetjournals.org/content/70/3/806.full
SO  - Mol Pharmacol2006 Sep 01; 70
AB  - Organic anion transporting polypeptide (OATP) superfamily member 2B1 (OATP2B1) mediates the uptake of steroid hormone precursors and selected drugs in the placenta, liver, mammary gland, brain, and intestine. This action is modulated by sulfhydryl reagents. Common to all OATPs is a large extracellular loop between transmembrane domains IX and X with 10 conserved cysteines. To elucidate the structure-function relationship of this cysteine rich ectodomain, a truncated OATP2B1 lacking 10 extracellular cysteines (OATP2B1Δ489-557) and 10 OATP2B1 mutants containing individual Cys-to-Ala substitutions were generated and expressed in CHO-K1 cells. The immunolocalization, cell-surface expression, transport activity, and free cysteine labeling with N-biotinoylaminoethylmethane-thiosulfonate of mutant proteins and wild-type OATP2B1 were compared. OATP2B1Δ489-557 accumulated intracellularly. Nine Cys-to-Ala substitutions, C489A, C495A, C504A, C516A, C520A, C539A, C541A, C553A, and C557A, were misprocessed, appearing predominantly as core-glycosylated, 60-kDa proteins and as 180-kDa complexes. Only C493A was a fully glycosylated 75-kDa protein expressed at the cell surface. Thapsigargin partially corrected the misprocessing of mutants. Compared with OATP2B1, C493A and C557A transported estrone-3-sulfate and dehydroepiandrosterone sulfate less efficiently, whereas all other mutants were functionally impaired. MTSEA labeled free cysteines in all Cys-to-Ala mutants but not in OATP2B1, suggesting that all 10 extracellular cysteines are normally disulfide-bonded. Our findings show that the trafficking and function of OATP2B1 is vulnerable to changes in the cysteine residues of extracellular loop IX-X. The American Society for Pharmacology and Experimental Therapeutics