Bacterial zinc transporters and regulators.
Zn2+ homeostasis in bacteria is achieved by export systems and uptake systems which are separately regulated by their own regulators. Three types of Zn2+ export systems that protect cells from high toxic concentrations of Zn2+ have been identified: RND multi-drug efflux transporters, P-type ATPases, and cation-diffusion facilitators. The RND type exporters for Zn2+ are only found in a few gram-negative bacteria; they allow a very efficient export across the cytoplasmic membrane and the outer membrane of the cell. P-type ATPases and cation-diffusion facilitators belong to protein families that are also found in eukaryotes. The exporters are regulated in bacteria by MerR-like repressor/activators or by ArsR-like repressors. For the high-affinity uptake of Zn2+, several binding-protein-dependent ABC transporters belonging to one class have been identified in different bacteria. Zn2+ ABC transporters are regulated by Zur repressors, which belong to the Fur protein family of iron regulators. Little is known about low-affinity Zn2+ uptake under zinc-replete conditions. One known example is the phosphate uptake system Pit, which may cotransport Zn2+ in Escherichia coli. Similarly, the citrate-metal cotransporter CitM in Bacillus subtilis may help to supply Zn2+.
Hantke
K
K
Mikrobiologie/Membranphysiologie, Universität Tübingen, Germany. hantke@uni-tuebingen.de
D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D001419:Bacteria / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D017136:Ion Transport; D008954:Models, Biological; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D015032:Zinc / Q000378:metabolism*
D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; C017800:zinc-binding protein; D000251:Adenosine Triphosphatases; D015032:Zinc