Transmembrane domain VII of the human apical sodium-dependent bile acid transporter ASBT (SLC10A2) lines the substrate translocation pathway.

摘要

Recent evidence implicating transmembrane (TM) segment 7 of the apical sodium-dependent bile acid transporter (ASBT) in substrate interaction warranted examination of its aqueous accessibility. Therefore, cysteine substitution of 22 consecutive amino acids was performed against a methanethiosulfonate (MTS)-resistant background (C270A). Activity and susceptibility to polar MTS derivatives [(2-aminoethyl)-methanethiosulfonate (MTSEA), [2-(trimethylammonium)ethyl]methanethiosulfonate (MTSET), and methanethiosulfonate ethylsulfonate (MTSES)] of mutants were evaluated in COS-1 cells. Thr289, Tyr293, Gln297, Ala301, Phe307, and Tyr308 represented loss-of-function mutants; furthermore, the measurable residual activities for T289C, Y293C, and A301C (