INVESTIGADORES
BLANCATO Victor Sebastian
artículos
Título:
Functional Characterization and Me2+ ion specificity of a Ca2+-citrate transporter from Enterococcus faecalis
Autor/es:
BLANCATO, VS; MAGNI, C; LOLKEMA, J
Revista:
FEBS LETTERS
Referencias:
Año: 2006 vol. 273 p. 5121 - 5130
ISSN:
0014-5793
Resumen:
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 that are
found in the phylum Firmicutes and that 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 motive force
driven uptake of the Ca2+-citrate complex with an affinity constant
of 3.5 µM. 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 the specificity of the Bacillus subtilis Ca2+-citrate transporter in the
same family. In spite of the high sequence identity with the Streptococcus
mutans Fe3+-citrate transporter, no transport activity with Fe3+
(or Fe2+) could be detected. The transporter of E. faecalis
catalyzes translocation of citrate in complex with Ca2+, Sr2+, Mn2+, Cd2+ and
Pb2+ and not with Mg2+, Zn2+, Ni2+
and Co2+. The specificity appears to correlate with the size of the
metal ion in the complex