Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 109, Issue 19, Pages 7202-7207Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1200362109
Keywords
Cd transport; metal binding site; zinc; Zn transporter; Cd toxicity
Categories
Funding
- Israel Science Foundation [985/07, 485/11]
- National Institute of Health [R01 GM065137]
- Office of Basic Energy Sciences, Department of Energy [DOE KC0304000]
- Kreitman foundation
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Zinc and cadmium are similar metal ions, but though Zn2+ is an essential nutrient, Cd2+ is a toxic and common pollutant linked to multiple disorders. Faster body turnover and ubiquitous distribution of Zn2+ vs. Cd2+ suggest that a mammalian metal transporter distinguishes between these metal ions. We show that the mammalian metal transporters, ZnTs, mediate cytosolic and vesicular Zn2+ transport, but reject Cd2+, thus constituting the first mammalian metal transporter with a refined selectivity against Cd2+. Remarkably, the bacterial ZnT ortholog, YiiP, does not discriminate between Zn2+ and Cd2+. A phylogenetic comparison between the tetrahedral metal transport motif of YiiP and ZnTs identifies a histidine at the mammalian site that is critical for metal selectivity. Residue swapping at this position abolished metal selectivity of ZnTs, and fully reconstituted selective Zn2+ transport of YiiP. Finally, we show that metal selectivity evolves through a reduction in binding but not the translocation of Cd2+ by the transporter. Thus, our results identify a unique class of mammalian transporters and the structural motif required to discriminate between Zn2+ and Cd2+, and show that metal selectivity is tuned by a coordination-based mechanism that raises the thermodynamic barrier to Cd2+ binding.
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