Mutational Analysis of Uncharged Polar Residues and Proline in the Distal One-Third (Thr130–Pro142) of the Highly Conserved Region of Mouse Slc10a2

Abstract

Solute carrier family member 2 (SLC10A2) reabsorbs bile acids at the distal terminus of the ileum in an Na(+)-dependent manner. Alignment of deduced amino acid sequences of SLC10 family members and homologous genes in various species revealed a highly conserved region that corresponds to Gly(104)-Pro(142) of SLC10A2. To elucidate the functional importance of this region, uncharged polar residues and Pro in the distal one-third of this region in mouse Slc10a2 (mSlc10a2) were submitted to mutational analysis, and taurocholic acid uptake and cell surface localization were evaluated. In addition to mutations that abolished almost all of the transport activity with and without cellular localization failure (P142V and T130A respectively), a mutation that perhaps affected affinity for taurocholic acid was identified (T134A). These results suggest that the highly conserved region contains residues involved in the substrate interaction, function, and cellular localization of mSlc10a2.