Discovery of the ergothioneine transporter

doi:10.1073/pnas.0408624102

Discovery of the ergothioneine transporter

^*Department of Pharmacology, University of Cologne, Gleueler Strasse 24, 50931 Cologne, Germany; ^§Pharma Research–Molecular Screening Technology, Bayer Healthcare, 42096 Wuppertal, Germany; ^∥Department of Internal Medicine I, University of Cologne, Kerpener Strasse 62, 50924 Cologne, Germany; and ^†Center for Molecular Medicine, University of Cologne, Joseph-Stelzmann-Strasse 52, 50931 Cologne, Germany

Edited by Anthony Cerami, The Kenneth S. Warren Institute, Kitchawan, NY, and approved February 23, 2005 (received for review November 22, 2004)

Abstract

Variants of the SLC22A4 gene are associated with susceptibility to rheumatoid arthritis and Crohn's disease. SLC22A4 codes for an integral membrane protein, OCTN1, that has been presumed to carry organic cations like tetraethylammonium across the plasma membrane. Here, we show that the key substrate of this transporter is in fact ergothioneine (ET). Human OCTN1 was expressed in 293 cells. A substrate lead, stachydrine (alias proline betaine), was identified by liquid chromatography MS difference shading, a new substrate search strategy. Analysis of transport efficiency of stachydrine-related solutes, affinity, and Na⁺ dependence indicates that the physiological substrate is ET. Efficiency of transport of ET was as high as 195 μl per min per mg of protein. By contrast, the carnitine transporter OCTN2 from rat did not transport ET at all. Because ET is transported >100 times more efficiently than tetraethylammonium and carnitine, we propose the functional name ETT (ET transporter) instead of OCTN1. ET, all of which is absorbed from food, is an intracellular antioxidant with metal ion affinity. Its particular purpose is unresolved. Cells with expression of ETT accumulate ET to high levels and avidly retain it. By contrast, cells lacking ETT do not accumulate ET, because their plasma membrane is virtually impermeable for this compound. The real-time PCR expression profile of human ETT, with strong expression in CD71⁺ cells, is consistent with a pivotal function of ET in erythrocytes. Moreover, prominent expression of ETT in monocytes and SLC22A4 polymorphism associations suggest a protective role of ET in chronic inflammatory disorders.

Footnotes

↵ ‡ To whom correspondence should be addressed. E-mail: dirk.gruendemann{at}uni-koeln.de.
↵ ¶ Present address: Department of Anaesthesia, University Hospital Düsseldorf, Moorenstrasse 5, 40225 Düsseldorf, Germany.
Author contributions: D.G., S.H., S.G., and A.G. designed research; D.G., S.H., S.G., and A.G. performed research; D.G., A.L., R.B., N.J., and A.R. contributed new reagents/analytic tools; D.G., S.H., S.G., A.G., and E.S. analyzed data; and D.G. wrote the paper.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: ET, ergothioneine; ETT, ET transporter; TEA, tetraethylammonium.