J. Bacteriol., Nov 1997, 6871-6879, Vol 179, No. 22
C Rensing, T Pribyl and DH Nies
The membrane-bound CzcCBA protein complex mediates heavy metal resistance
in Alcaligenes eutrophus by an active cation efflux mechanism driven by
cation-proton antiport. The CzcA protein alone is able to mediate weak
resistance to zinc and cobalt and is thus the central antiporter subunit.
The two histidine-rich motifs in the CzcB subunit are not essential for
zinc resistance; however, deletion of both motifs led to a small but
significant loss of resistance to this cation. Translation of the czcC gene
encoding the third subunit of the CzcCBA complex starts earlier than
predicted, and CzcC is probably a periplasmic protein, as judged by the
appearance of two bands after expression of czcC in Escherichia coli under
control of the phage T7 promoter. Fusions of CzcC and CzcB with alkaline
phosphatase and beta- galactosidase are in agreement with a periplasmic
location of most parts of both proteins. Both CzcC and CzcB are bound to a
membrane, probably the outer membrane, by themselves and do not need either
CzcA or each other as an anchoring protein. Based on these data, a new
working model for the function of the Czc system is discussed.
Copyright © 1997, American Society for Microbiology
New functions for the three subunits of the CzcCBA cation-proton antiporter
Institut fur Mikrobiologie, Halle, Germany.
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