SLCO1B3-SLCO1B7 readthrough transcript protein; liver specific transporter-3 transmembrane 12; LST-3TM12; organic anion transporting polypeptide 1B3-1B7; OATP1B3-1B7; solute carrier organic anion transporter family member 1B3-1B7; SLCO1B3-SLCO1B7 (SLCO1B3-SLCO1B7)

Function

• mediates Na+-independent uptake of organic anions
• transports the conjugated steroids 17-beta-glucuronosyl estradiol (17-beta-estradiol, 17-O-(beta-D-glucuronate or E2G) & DHEA-3-sulfate (DHEAS) at the smooth endoplasmic reticulum membrane (SER), granting access to metabolizing enzymes
• contributes to the metabolism of bile acids such as taurocholate (cholyltaurine) & lithocholate, by functioning as a doorway between SER & cytosol, thus decreasing their circulating levels & protecting the organism from their detergent properties
• regulates access or exit of drugs to the SER lumen

• transport activity is induced by farnesoid X receptor (FXR) agonists such as chenodeoxycholate

• Kinetic parameters:
  • KM=32.8 uM for 17beta-estradiol 17-O-(beta-D-glucuronate)
  • KM=34.2 uM for dehydroepiandrosterone sulfate
  • KM=20.4 uM for dehydroepiandrosterone sulfate
  • KM=15.99 uM for taurocholate
  • Vmax=29.7 pmol/min/mg protein with 17beta-estradiol 17-O-(beta-D-glucuronate)
  • Vmax=300.2 pmol/min/mg protein with dehydroepiandrosterone sulfate
  • Vmax=264.3 pmol/min/mg protein with dehydroepiandrosterone sulfate
  • Vmax=17.38 pmol/min/mg protein with taurocholate

17-beta-estradiol 17-O-(beta-D-glucuronate)(out) = 17-beta-estradiol 17-O-(beta-D-glucuronate)(in)

DHEA-3-sulfate(out) = DHEA-3-sulfate(in)

taurocholate(out) = taurocholate(in)

lithocholate(out) = lithocholate(in)

Structure

• belongs to the organo anion transporter (TC 2.A.60) family

Compartment

• smooth endoplasmic reticulum membrane, multi-pass membrane protein
• cell membrane, multi-pass membrane protein
• endoplasmic reticulum membrane, multi-pass membrane protein

Alternative splicing

• named isoforms=4: SLCO1B3-SLCO1B7-1, SLCO1B3-1, SLCO1B3-2, SLCO1B7-1

Expression

• expressed in the perivenular areas (centrilobular) of the liver (at protein level)

Notes

• based on a naturally occurring readthrough transcript which produces an SLCO1B3-SLCO1B7 fusion protein where the first 5 exons originate from SLCO1B3, while SLCO1B7 provides the remaining exons
  • the resulting mRNA encodes for a functional transporter SLCO1B3-SLCO1B7

More general terms

• glycoprotein
• transmembrane 12 protein
• carrier protein (transporter)

Database

• UniProt: http://www.uniprot.org/uniprot/F5H094.html