TAILIEUCHUNG - Báo cáo khoa học: Functional characterization and Me2+ ion specificity of a Ca2+–citrate transporter from Enterococcus faecalis1

Secondary transporters of the bacterial CitMHS family transport citrate in complex with a metal ion. Different members of the family are specific for the metal ion in the complex and have been shown to transport Mg 2+ –cit-rate, Ca 2+ –citrate or Fe 3+ –citrate. The Fe 3+ –citrate transporter ofStrep-tococcus mutans clusters on the phylogenetic tree on a separate branch with a group of transporters found in the phylum Firmicutes which are believed to be involved in anaerobic citrate degradation. . | ỊFEBS Journal Functional characterization and Me2 ion specificity of a Ca2 -citrate transporter from Enterococcus faecalis Victor S. Blancato1 2 Christian Magni2 and Juke S. Lolkema1 1 Molecular Microbiology Groningen Biomolecular Sciences and Biotechnology Institute University of Groningen Haren the Netherlands 2 Instituto de Biologia Molecular y Celular de Rosario IBR-CONICET and Departamento de Microbiologia Facultad de Ciencias Bioquimicas y Farmaceuticas Universidad Nacionalde Rosario Argentina Keywords CITMHS family citrate fermentation citrate transport Enterococcus faecalis Me-citrate complex Correspondence J. S. Lolkema Molecular Microbiology BiologicalCentre Kerklaan 30 9741NN Haren the Netherlands Fax 31 50 3632154 Tel 31 50 3632155 E-mail Received 10 August 2006 revised 18 September 2006 accepted 20 September 2006 doi Secondary transporters of the bacterial CitMHS family transport citrate in complex with a metal ion. Different members of the family are specific for the metal ion in the complex and have been shown to transport Mg2 -citrate Ca2 -citrate or Fe3 -citrate. The Fe3 -citrate transporter of Streptococcus mutans clusters on the phylogenetic tree on a separate branch with a group of transporters found in the phylum Firmicutes which are believed to be involved in anaerobic citrate degradation. We have cloned and characterized the transporter from Enterococcus faecalis EfCitH in this cluster. The gene was functionally expressed in Escherichia coli and studied using right-side-out membrane vesicles. The transporter catalyzes proton-motiveforce-driven uptake of the Ca2 -citrate complex with an affinity constant of pM. Homologous exchange is catalyzed with a higher efficiency than efflux down a concentration gradient. Analysis of the metal ion specificity of EfCitH activity in right-side-out membrane vesicles revealed a specificity that was highly similar to that of the Bacillus subtilis Ca2 .

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