2. Academic Validation
  3. A novel mode of operation of SLC22A11: Membrane insertion of estrone sulfate versus translocation of uric acid and glutamate

A novel mode of operation of SLC22A11: Membrane insertion of estrone sulfate versus translocation of uric acid and glutamate

  • Biochem Pharmacol. 2017 Mar 15;128:74-82. doi: 10.1016/j.bcp.2016.12.020.
Peter Skwara 1,  Edgar Schömig 1,  Dirk Gründemann 2
Affiliations

Affiliations

  • 1 Department of Pharmacology, University of Cologne, Gleueler Straße 24, 50931 Cologne, Germany.
  • 2 Department of Pharmacology, University of Cologne, Gleueler Straße 24, 50931 Cologne, Germany. Electronic address: [email protected].
PMID: 28027879 DOI: 10.1016/j.bcp.2016.12.020
Abstract

Estrone sulfate alias estrone-3-sulfate (E3S) is considerably larger and much more hydrophobic than typical substrates of SLC22 transporters. It is puzzling that many otherwise unrelated transporters have been reported to transport E3S. Here we scrutinized the mechanism of transport of E3S by SLC22A11 (alias OAT4), by direct comparison with uric acid (UA), an important physiological substrate. Heterologous expression of SLC22A11 in human 293 cells gave rise to a huge unidirectional efflux of glutamate (Glu) and aspartate, as determined by LC-MS/MS. The uptake of E3S was 20-fold faster than the uptake of UA. Yet, the outward transport of Glu was inhibited by extracellular E3S, but not by UA. The release of E3S after preloading was trans-stimulated by extracellular dehydroepiandrosterone sulfate (DHEAS), but neither by UA nor 6-carboxyfluorescein (6CF). The equilibrium accumulation of E3S was enhanced 3-fold by replacement of chloride with gluconate, but the opposite effect was observed for UA. These results establish that SLC22A11 provides entirely different transport mechanisms for E3S and UA. Therefore, E3S must not be used as a substitute for UA to assay the function of SLC22A11. In equilibrium accumulation experiments, the transporter-mediated uptake was a linear function of the concentration of UA and 6CF. By contrast, in the same concentration range the graph for E3S was hyperbolic. This suggests that SLC22A11 inserts E3S into a small volume with limited capacity, the plasma membrane. Our data support the notion that the reverse process, extraction from the membrane, is also catalyzed by the carrier.

Keywords

6-Carboxyfluorescein (PubChem CID: 76806); Aspartic acid (PubChem CID: 5960); DHEAS (PubChem CID: 12594); Estrone sulfate; Estrone sulfate (PubChem CID: 3001028); Glutamic acid; Glutamic acid (PubChem CID: 33032); Plasma membrane; SLC22A11; Solute transport; Uric acid; Uric acid (PubChem CID: 1175).

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