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J. Biol. Chem., Vol. 282, Issue 5, 2832-2839, February 2, 2007

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Functional and Structural Characterization of a Prokaryotic Peptide Transporter with Features Similar to Mammalian PEPT1^*

Dietmar Weitz¹, Daniel Harder¹, Fabio Casagrande, Dimitrios Fotiadis, Petr Obrdlik^¶, Bela Kelety^¶, and Hannelore Daniel²

From the Molecular Nutrition Unit, Department of Food and Nutrition, Technical University of Munich, 85350 Freising, Germany, M. E. Müller Institute for Structural Biology, Biozentrum, University of Basel, CH-4056 Basel, Switzerland, and ^¶Iongate Biosciences GmbH, D528 Industriepark Höchst, D-65926 Frankfurt, Germany

The ydgR gene of Escherichia coli encodes a protein of the proton-dependent oligopeptide transporter (POT) family. We cloned YdgR and overexpressed the His-tagged fusion protein in E. coli BL21 cells. Bacterial growth inhibition in the presence of the toxic phosphonopeptide alafosfalin established YgdR functionality. Transport was abolished in the presence of the proton ionophore carbonyl cyanide p-chlorophenylhydrazone, suggesting a proton-coupled transport mechanism. YdgR transports selectively only di- and tripeptides and structurally related peptidomimetics (such as aminocephalosporins) with a substrate recognition pattern almost identical to the mammalian peptide transporter PEPT1. The YdgR protein was purified to homogeneity from E. coli membranes. Blue native-polyacrylamide gel electrophoresis and transmission electron microscopy of detergent-solubilized YdgR suggest that it exists in monomeric form. Transmission electron microscopy revealed a crown-like structure with a diameter of 8 nm and a central density. These are the first structural data obtained from a proton-dependent peptide transporter, and the YgdR protein seems an excellent model for studies on substrate and inhibitor interactions as well as on the molecular architecture of cell membrane peptide transporters.

Received for publication, May 19, 2006 , and in revised form, October 13, 2006.

^* This work was supported by the Sixth Framework Programme of the European Union (European Genomics Initiative on Disorders of Plasma Membrane Amino Acid Transporters). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ These authors contributed equally to this work.

² To whom correspondence should be addressed: Molecular Nutrition Unit, Dept. of Food and Nutrition, Am Forum 5, D-85350 Freising-Weihenstephan, Germany. Tel.: 49-8161713401; Fax: 49-8161713999; E-mail: daniel{at}wzw.tum.de.

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