Global functions of extracellular, transmembrane and cytoplasmic domains of organic solute transporter β-subunit

Biochem J. 2017 May 25;474(12):1981-1992. doi: 10.1042/BCJ20161093.


Transport of bile acids across the basolateral membrane of the intestinal enterocyte is carried out by the organic solute transporter (Ost) composed of a seven-transmembrane domain (TMD) subunit (Ostα) and an ancillary single TMD subunit (Ostβ). Although previous investigations have demonstrated the importance of the TMD of Ostβ for its activity, further studies were conducted to assess the contributions of other regions of the Ostβ subunit. Transport activity was retained when Ostβ was truncated to contain only the TMD with 15 additional residues on each side and co-expressed with Ostα, whereas shorter fragments were inactive. To probe the broader functions of Ostβ segments, chimeric proteins were constructed in which N-terminal, TMD or C-terminal regions of Ostβ were fused to corresponding regions of receptor activity-modifying protein (RAMP1), a single TMD protein required by several seven-TMD G-protein-coupled receptors including the calcitonin receptor-like receptor (CLR). Ostβ/RAMP1 chimeras were expressed with Ostα and CLR. As expected, replacing the Ostβ TMD abolished transport activity; however, replacing either the entire N-terminal or entire C-terminal domain of Ostβ with RAMP1 sequences did not prevent plasma membrane localization or the ability to support [3H]taurocholate uptake. Co-immunoprecipitation experiments revealed that the C-terminus of Ostβ is a previously unrecognized site of interaction with Ostα. All chimeras containing N-terminal RAMP1 segments allowed co-expressed CLR to respond to agonists with strong increases in cyclic AMP. These results provide new insights into the structure and function of the heteromeric Ost transporter complex.

Keywords: G-protein-coupled receptors; bile acids; calcitonin receptor-like receptor; membrane transport; organic solute transporter; receptor activity-modifying protein.

MeSH terms

  • Absorption, Physiological / drug effects
  • Animals
  • Bile Acids and Salts / metabolism*
  • Biological Transport / drug effects
  • Calcitonin Gene-Related Peptide / genetics
  • Calcitonin Gene-Related Peptide / metabolism
  • Calcitonin Receptor-Like Protein / agonists
  • Calcitonin Receptor-Like Protein / genetics
  • Calcitonin Receptor-Like Protein / metabolism
  • Cyclic AMP / metabolism
  • HEK293 Cells
  • Humans
  • Immunoprecipitation
  • Membrane Transport Proteins / chemistry
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / metabolism*
  • Mice
  • Peptide Fragments / chemistry
  • Peptide Fragments / genetics
  • Peptide Fragments / metabolism
  • Protein Interaction Domains and Motifs
  • Protein Transport
  • Receptor Activity-Modifying Protein 1 / chemistry
  • Receptor Activity-Modifying Protein 1 / genetics
  • Receptor Activity-Modifying Protein 1 / metabolism
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / metabolism
  • Second Messenger Systems / drug effects
  • Structural Homology, Protein
  • Taurocholic Acid / metabolism
  • Tritium


  • Bile Acids and Salts
  • CALCA protein, human
  • CALCRL protein, human
  • Calcitonin Receptor-Like Protein
  • Membrane Transport Proteins
  • Peptide Fragments
  • Ramp1 protein, mouse
  • Receptor Activity-Modifying Protein 1
  • Recombinant Fusion Proteins
  • organic solute transporter alpha, mouse
  • organic solute transporter beta, mouse
  • Tritium
  • Taurocholic Acid
  • Cyclic AMP
  • Calcitonin Gene-Related Peptide