Dirk Gründemann, Ph.D., Department of Pharmacology, University Hospital, University of Cologne, Germany
Dr. Dirk Gründemann
Professor Dirk Gründemann works at the Department of Pharmacology, University Hospital, University of Cologne, Germany. The discovery of the human ergothioneine transporter in his lab represented an important advance in the field of ergothioneine research. Fascinated by this unique antioxidant, he brings together mass spectrometry and molecular biology methods to investigate the purpose and potential of ergothioneine.
Dr. Gründemann studied Biochemistry in Hannover, Germany. As a doctoral fellow of Hermann Koepsell at the Max Planck Institute for Biophysics, he became deeply interested in human transport proteins of the plasma membrane. He received his Ph.D. in Biochemistry in 1994 from the Johann Wolfgang Goethe University, Frankfurt, Germany. Research on transporters evolved as a postdoctoral fellow of Edgar Schömig at the Department of Pharmacology, University of Heidelberg, Germany. In 2001, he received his Habilitation in Molecular Pharmacology and Toxicology. Also in 2001, the group moved to Cologne, where Dr. Gründemann heads his own group since 2006. In 2006, he was appointed to the equivalent of Associate Professor. He received the Galenus von Pergamon Prize in 2005 for the discovery of the ergothioneine transporter by LC/MS Difference Shading.
When
November 2, 2017
Abstract
Ergothioneine - developed by nature to do what exactly?
We have a long-standing interest in human transport proteins of the plasma membrane. Based on a novel LC-MS strategy, we discovered ETT (human gene symbol SLC22A4), a powerful (driven by the sodium gradient) and highly specific (based on transport efficiency) transporter for the uptake of ergothioneine (ET) into human cells. Cells lacking ETT do not accumulate ET since phospholipid bilayers are virtually impermeable to this hydrophilic zwitterion. In the human body ETT is not found everywhere; top expression sites are the erythrocyte progenitor cells of bone marrow, the small intestine (ileum), trachea, kidney, cerebellum, lung, and monocytes. ETT thus mediates absorption, distribution, and retention of ET.
ET is a natural compound that humans cannot synthesize; it must be absorbed from food. Most of our contemporary food contains very little ET, but several mushrooms and cyanobacteria contain around 1 mg/g dried material. After ingestion, ET is rapidly cleared from the circulation and then retained in the body with minimal metabolism.
ET can be considered a derivative of thiourea. During the biosynthesis of ET, L-histidine is converted to a betaine and a sulfur atom is attached to position 2 of the imidazole ring. Because of the prevailing thione (doubly bonded sulfur) tautomer, ET has several properties that are markedly different from ordinary thiols like the ubiquitous glutathione (GSH).
The mere existence of ETT and its evolutionary conservation across all vertebrates imply that ET fulfills a beneficial role - like a vitamin. Case-control studies suggest that polymorphisms in the SLC22A4 gene are associated with susceptibility to chronic inflammatory diseases, such as Crohn's disease, ulcerative colitis, and type I diabetes, but it is unknown whether these mutations promote disease. In general, ET is considered an intracellular antioxidant. However, its precise physiological purpose is still unresolved. The key questions that guide our research are: why do we accumulate ET in particular cells despite a 10-fold excess of GSH, the general antioxidant? What is the unique benefit from ET?
Recently, we have reported that in the skin of unstressed ETT knockout zebrafish, the content of 8-oxoguanine (8OG; alias 8-oxo-7,8-dihydroguanine) was increased 4-fold vs. wild-type. This led to the hypothesis that the specific purpose of ET, universal across all species, could be to eradicate noxious singlet oxygen (1O2). 1O2 is a member of the ROS (reactive oxygen species) quartet; it is less reactive than the hydroxyl radical, but more aggressive than the superoxide anion and hydrogen peroxide. It's easy to kill cultured cells with 1O2: just add some photosensitizer, turn on the light and wait for a couple of minutes. While the hydroxyl radical reacts with almost anything, 1O2 is selective about its reaction partner. For example, the hydroxyl radical attacks all 4 DNA bases, but 1O2 confines itself to guanine. ET could be the perfect hydrophilic reagent to prevent damage at intracellular sites of high singlet oxygen generation. This concept also explains why cyanobacteria developed ET in the first place: these were the first living things that had to cope with oxygen.
We have started to test our hypothesis. In our latest study we have identified by LC-MS the products of ET and 1O2 that are generated in aqueous solution at 37 °C and physiological pH. Regeneration of ET seems feasible, since some ET products - by contrast to hercynine (= ET minus sulfur) products - decomposed easily in the MS collision cell to become aromatic again. The generation of distinct products from ET, but not from hercynine, was fully resistant to a large molar excess of TRIS or GSH. This suggests that 1O2 markedly favors ET over GSH (at least 50-fold) and TRIS (at least 250-fold) for the initial reaction. It follows that ET should provide much better protection against 1O2 than GSH. The universal value and uniqueness of ET may reside exactly here - much less reactive in general than GSH, but much more reactive with the fitting molecule.
