Publications by authors named "Alexander Ehrmann"

7 Publications

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Pharmacological inhibition of Vanin-1 is not protective in models of acute and chronic kidney disease.

Am J Physiol Renal Physiol 2021 01 16;320(1):F61-F73. Epub 2020 Nov 16.

Research and Early Development, Bayer Pharmaceuticals, Wuppertal, Germany.

Oxidative stress is a key concept in basic, translational, and clinical research to understand the pathophysiology of various disorders, including cardiovascular and renal diseases. Although attempts to directly reduce oxidative stress with redox-active substances have until now largely failed to prove clinical benefit, indirect approaches to combat oxidative stress enzymatically have gained further attention as potential therapeutic strategies. The pantetheinase Vanin-1 is expressed on kidney proximal tubular cells, and its reaction product cysteamine is described to negatively affect redox homeostasis by inhibiting the replenishment of cellular antioxidative glutathione stores. Vanin-1-deficient mice were shown to be protected against oxidative stress damage. The aim of this study was to elucidate whether pharmacological inhibition of Vanin-1 protects mice from oxidative stress-related acute or chronic kidney injury as well. By studying renal ischemia-reperfusion injury in Col4α3 (Alport syndrome) mice and in vitro hypoxia-reoxygenation in human proximal tubular cells we found that treatment with a selective and potent Vanin-1 inhibitor resulted in ample inhibition of enzymatic activity in vitro and in vivo. However, surrogate parameters of metabolic and redox homeostasis were only partially and insufficiently affected. Consequently, apoptosis and reactive oxygen species level in tubular cells as well as overall kidney function and fibrotic processes were not improved by Vanin-1 inhibition. We thus conclude that Vanin-1 functionality in the context of cardiovascular diseases needs further investigation and the biological relevance of pharmacological Vanin-1 inhibition for the treatment of kidney diseases remains to be proven.
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http://dx.doi.org/10.1152/ajprenal.00373.2020DOI Listing
January 2021

The RESOLUTE consortium: unlocking SLC transporters for drug discovery.

Authors:
Giulio Superti-Furga Daniel Lackner Tabea Wiedmer Alvaro Ingles-Prieto Barbara Barbosa Enrico Girardi Ulrich Goldmann Bettina Gürtl Kristaps Klavins Christoph Klimek Sabrina Lindinger Eva Liñeiro-Retes André C Müller Svenja Onstein Gregor Redinger Daniela Reil Vitaly Sedlyarov Gernot Wolf Matthew Crawford Robert Everley David Hepworth Shenping Liu Stephen Noell Mary Piotrowski Robert Stanton Hui Zhang Salvatore Corallino Andrea Faedo Maria Insidioso Giovanna Maresca Loredana Redaelli Francesca Sassone Lia Scarabottolo Michela Stucchi Paola Tarroni Sara Tremolada Helena Batoulis Andreas Becker Eckhard Bender Yung-Ning Chang Alexander Ehrmann Anke Müller-Fahrnow Vera Pütter Diana Zindel Bradford Hamilton Martin Lenter Diana Santacruz Coralie Viollet Charles Whitehurst Kai Johnsson Philipp Leippe Birgit Baumgarten Lena Chang Yvonne Ibig Martin Pfeifer Jürgen Reinhardt Julian Schönbett Paul Selzer Klaus Seuwen Charles Bettembourg Bruno Biton Jörg Czech Hélène de Foucauld Michel Didier Thomas Licher Vincent Mikol Antje Pommereau Frédéric Puech Veeranagouda Yaligara Aled Edwards Brandon J Bongers Laura H Heitman Ad P IJzerman Huub J Sijben Gerard J P van Westen Justine Grixti Douglas B Kell Farah Mughal Neil Swainston Marina Wright-Muelas Tina Bohstedt Nicola Burgess-Brown Liz Carpenter Katharina Dürr Jesper Hansen Andreea Scacioc Giulia Banci Claire Colas Daniela Digles Gerhard Ecker Barbara Füzi Viktoria Gamsjäger Melanie Grandits Riccardo Martini Florentina Troger Patrick Altermatt Cédric Doucerain Franz Dürrenberger Vania Manolova Anna-Lena Steck Hanna Sundström Maria Wilhelm Claire M Steppan

Nat Rev Drug Discov 2020 07;19(7):429-430

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http://dx.doi.org/10.1038/d41573-020-00056-6DOI Listing
July 2020

Evolutionary Morphing of Tryptophan Synthase: Functional Mechanisms for the Enzymatic Channeling of Indole.

J Mol Biol 2018 12 25;430(24):5066-5079. Epub 2018 Oct 25.

Department of Biology, University of Konstanz, 78457 Konstanz, Germany; Institute of Integrative Biology, University of Liverpool, Crown Street, Liverpool, L69 7ZB, UK. Electronic address:

Tryptophan synthase (TrpS) is a heterotetrameric αββα enzyme that exhibits complex substrate channeling and allosteric mechanisms and is a model system in enzymology. In this work, we characterize proposed early and late evolutionary states of TrpS and show that they have distinct quaternary structures caused by insertions-deletions of sequence segments (indels) in the β-subunit. Remarkably, indole hydrophobic channels that connect α and β active sites have re-emerged in both TrpS types, yet they follow different paths through the β-subunit fold. Also, both TrpS geometries activate the α-subunit through the rearrangement of loops flanking the active site. Our results link evolutionary sequence changes in the enzyme subunits with channeling and allostery in the TrpS enzymes. The findings demonstrate that indels allow protein quaternary architectures to escape "minima" in the evolutionary landscape, thereby overcoming the conservational constraints imposed by existing functional interfaces and being free to morph into new mechanistic enzymes.
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http://dx.doi.org/10.1016/j.jmb.2018.10.013DOI Listing
December 2018

Identification of KCa3.1 Channel as a Novel Regulator of Oxidative Phosphorylation in a Subset of Pancreatic Carcinoma Cell Lines.

PLoS One 2016 5;11(8):e0160658. Epub 2016 Aug 5.

Drug Discovery, Therapeutic Research Groups / Onc II, Bayer Pharma AG, Berlin, Germany.

Pancreatic ductal adenocarcinoma (PDAC) represents the most common form of pancreatic cancer with rising incidence in developing countries and overall 5-year survival rates of less than 5%. The most frequent mutations in PDAC are gain-of-function mutations in KRAS as well as loss-of-function mutations in p53. Both mutations have severe impacts on the metabolism of tumor cells. Many of these metabolic changes are mediated by transporters or channels that regulate the exchange of metabolites and ions between the intracellular compartment and the tumor microenvironment. In the study presented here, our goal was to identify novel transporters or channels that regulate oxidative phosphorylation (OxPhos) in PDAC in order to characterize novel potential drug targets for the treatment of these cancers. We set up a Seahorse Analyzer XF based siRNA screen and identified previously described as well as novel regulators of OxPhos. The siRNA that resulted in the greatest change in cellular oxygen consumption was targeting the KCNN4 gene, which encodes for the Ca2+-sensitive K+ channel KCa3.1. This channel has not previously been reported to regulate OxPhos. Knock-down experiments as well as the use of a small molecule inhibitor confirmed its role in regulating oxygen consumption, ATP production and cellular proliferation. Furthermore, PDAC cell lines sensitive to KCa3.1 inhibition were shown to express the channel protein in the plasma membrane as well as in the mitochondria. These differences in the localization of KCa3.1 channels as well as differences in the regulation of cellular metabolism might offer opportunities for targeted therapy in subsets of PDAC.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0160658PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4975431PMC
August 2017

BAY 87-2243, a highly potent and selective inhibitor of hypoxia-induced gene activation has antitumor activities by inhibition of mitochondrial complex I.

Cancer Med 2013 Oct 20;2(5):611-24. Epub 2013 Aug 20.

Bayer Pharma AG, Global Drug Discovery, Wuppertal, Germany.

The activation of the transcription factor hypoxia-inducible factor-1 (HIF-1) plays an essential role in tumor development, tumor progression, and resistance to chemo- and radiotherapy. In order to identify compounds targeting the HIF pathway, a small molecule library was screened using a luciferase-driven HIF-1 reporter cell line under hypoxia. The high-throughput screening led to the identification of a class of aminoalkyl-substituted compounds that inhibited hypoxia-induced HIF-1 target gene expression in human lung cancer cell lines at low nanomolar concentrations. Lead structure BAY 87-2243 was found to inhibit HIF-1α and HIF-2α protein accumulation under hypoxic conditions in non-small cell lung cancer (NSCLC) cell line H460 but had no effect on HIF-1α protein levels induced by the hypoxia mimetics desferrioxamine or cobalt chloride. BAY 87-2243 had no effect on HIF target gene expression levels in RCC4 cells lacking Von Hippel-Lindau (VHL) activity nor did the compound affect the activity of HIF prolyl hydroxylase-2. Antitumor activity of BAY 87-2243, suppression of HIF-1α protein levels, and reduction of HIF-1 target gene expression in vivo were demonstrated in a H460 xenograft model. BAY 87-2243 did not inhibit cell proliferation under standard conditions. However under glucose depletion, a condition favoring mitochondrial ATP generation as energy source, BAY 87-2243 inhibited cell proliferation in the nanomolar range. Further experiments revealed that BAY 87-2243 inhibits mitochondrial complex I activity but has no effect on complex III activity. Interference with mitochondrial function to reduce hypoxia-induced HIF-1 activity in tumors might be an interesting therapeutic approach to overcome chemo- and radiotherapy-resistance of hypoxic tumors.
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http://dx.doi.org/10.1002/cam4.112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3892793PMC
October 2013

Ligand-induced formation of a transient tryptophan synthase complex with αββ subunit stoichiometry.

Biochemistry 2010 Dec 6;49(51):10842-53. Epub 2010 Dec 6.

Institute of Biophysics and Physical Biochemistry, University of Regensburg, Universitätsstrasse 31, D-93053 Regensburg, Germany.

The prototypical tryptophan synthases form a stable heterotetrameric αββα complex in which the constituting TrpA and TrpB1 subunits activate each other in a bidirectional manner. The hyperthermophilic archaeon Sulfolobus solfataricus does not contain a TrpB1 protein but instead two members of the phylogenetically distinct family of TrpB2 proteins, which are encoded within (sTrpB2i) and outside (sTrpB2a) the tryptophan operon. It has previously been shown that sTrpB2a does not functionally or structurally interact with sTrpA, whereas sTrpB2i substantially activates sTrpA in a unidirectional manner. However, in the absence of catalysis, no physical complex between sTrpB2i and sTrpA could be detected. In order to elucidate the structural requirements for complex formation, we have analyzed the interaction between sTrpA (α-monomer) and sTrpB2i (ββ-dimer) by means of spectroscopy, analytical gel filtration, and analytical ultracentrifugation, as well as isothermal titration calorimetry. In the presence of the TrpA ligand glycerol 3-phosphate (GP) and the TrpB substrate l-serine, sTrpA and sTrpB2i formed a physical complex with a thermodynamic dissociation constant of about 1 μM, indicating that the affinity between the α- and ββ-subunits is weaker by at least 1 order of magnitude than the affinity between the corresponding subunits of prototypical tryptophan synthases. The observed stoichiometry of the complex was 1 subunit of sTrpA per 2 subunits of sTrpB2i, which corresponds to a αββ quaternary structure and testifies to a strong negative cooperativity for the binding of the α-monomers to the ββ-dimer. The analysis of the interaction between sTrpB2i and sTrpA in the presence of several substrate, transition state, and product analogues suggests that the αββ complex remains stable during the whole catalytic cycle and disintegrates into α- and ββ-subunits upon the release of the reaction product tryptophan. The formation of a transient tryptophan synthase complex, together with the observed low affinity of sTrpB2i for l-serine, couples the rate of tryptophan biosynthesis in S. solfataricus to the cytosolic availability of l-serine.
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http://dx.doi.org/10.1021/bi1016815DOI Listing
December 2010

Dissection of glutathione conjugate turnover in yeast.

Phytochemistry 2010 Jan 10;71(1):54-61. Epub 2009 Nov 10.

Lehrstuhl für Botanik, Technische Universität München, Am Hochanger 4, D-85354 Freising, Germany.

Xenobiotics are widely used as pesticides. The detoxification of xenobiotics frequently involves conjugation to glutathione prior to compartmentalization and catabolism. In plants, degradation of glutathione-S-conjugates is initiated either by aminoterminal or carboxyterminal amino acid cleavage catalyzed by a gamma-glutamyl transpeptidase and phytochelatin synthase, respectively. In order to establish yeast as a model system for the analysis of the plant pathway, we used monochlorobimane as a model xenobiotic in Saccharomyces cerevisiae and mutants thereof. The catabolism of monochlorobimane is initiated by conjugation to form glutathione-S-bimane, which is then turned over into a gamma-GluCys-bimane conjugate by the vacuolar serine carboxypeptidases CPC and CPY. Alternatively, the glutathione-S-bimane conjugate is catabolized by the action of the gamma-glutamyl transpeptidase Cis2p to a CysGly-conjugate. The turnover of glutathione-S-bimane was impaired in yeast cells deficient in Cis2p and completely abolished by the additional inactivation of CPC and CPY in the corresponding triple knockout. Inducible expression of the Arabidopsis phytochelatin synthase AtPCS1 in the triple knockout resulted in the turnover of glutathione-S-bimane to the gamma-GluCys-bimane conjugate as observed in plants. Challenge of AtPCS1-expressing yeast cells with zinc, cadmium, and copper ions, which are known to activate AtPCS1, enhanced gamma-GluCys-bimane accumulation. Thus, initial catabolism of glutathione-S-conjugates is similar in plants and yeast, and yeast is a suitable system for a study of enzymes of the plant pathway.
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http://dx.doi.org/10.1016/j.phytochem.2009.09.034DOI Listing
January 2010