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Journal of Bacteriology, March 2006, p. 2198-2206, Vol. 188, No. 6
0021-9193/06/$08.00+0     doi:10.1128/JB.188.6.2198-2206.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

The Mechanism of the Tyrosine Transporter TyrP Supports a Proton Motive Tyrosine Decarboxylation Pathway in Lactobacillus brevis

Wout A. M. Wolken,¹ Patrick M. Lucas,² Aline Lonvaud-Funel,² and Juke S. Lolkema^1*

Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Haren, The Netherlands,¹ Faculté d'Oenologie, INRA-Université Victor Segalen Bordeaux, Talence, France²

Received 30 November 2005/ Accepted 4 January 2006

The tyrosine decarboxylase operon of Lactobacillus brevis IOEB9809 contains, adjacent to the tyrosine decarboxylase gene, a gene for TyrP, a putative tyrosine transporter. The two genes potentially form a proton motive tyrosine decarboxylation pathway. The putative tyrosine transporter gene of L. brevis was expressed in Lactococcus lactis and functionally characterized using right-side-out membranes. The transporter very efficiently catalyzes homologous tyrosine-tyrosine exchange and heterologous exchange between tyrosine and its decarboxylation product tyramine. Tyrosine-tyramine exchange was shown to be electrogenic. In addition to the exchange mode, the transporter catalyzes tyrosine uniport but at a much lower rate. Analysis of the substrate specificity of the transporter by use of a set of 19 different tyrosine substrate analogues showed that the main interactions between the protein and the substrates involve the amino group and the phenyl ring with the para hydroxyl group. The carboxylate group that is removed in the decarboxylation reaction does not seem to contribute to the affinity of the protein for the substrates significantly. The properties of the TyrP protein are those typical for precursor-product exchangers that operate in proton motive decarboxylation pathways. It is proposed that tyrosine decarboxylation in L. brevis results in proton motive force generation by an indirect proton pumping mechanism.

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* Corresponding author. Mailing address: Molecular Microbiology, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands. Phone: 31 50 3632155. Fax: 31 50 3632154. E-mail: j.s.lolkema{at}rug.nl.

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Journal of Bacteriology, March 2006, p. 2198-2206, Vol. 188, No. 6
0021-9193/06/$08.00+0     doi:10.1128/JB.188.6.2198-2206.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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