Selective electrodiffusion of zinc ions in a Zrt-, Irt-like protein, ZIPB.
All living cells need zinc ions to support cell growth. Zrt-, Irt-like proteins (ZIPs) represent a major route for entry of zinc ions into cells, but how ZIPs promote zinc uptake has been unclear. Here we report the molecular characterization of ZIPB from Bordetella bronchiseptica, the first ZIP homolog to be purified and functionally reconstituted into proteoliposomes. Zinc flux through ZIPB was found to be nonsaturable and electrogenic, yielding membrane potentials as predicted by the Nernst equation. Conversely, membrane potentials drove zinc fluxes with a linear voltage-flux relationship. Direct measurements of metal uptake by inductively coupled plasma mass spectroscopy demonstrated that ZIPB is selective for two group 12 transition metal ions, Zn(2+) and Cd(2+), whereas rejecting transition metal ions in groups 7 through 11. Our results provide the molecular basis for cellular zinc acquisition by a zinc-selective channel that exploits in vivo zinc concentration gradients to move zinc ions into the cytoplasm.
Lin
Wei
W
Biology Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
Chai
Jin
J
Love
James
J
Fu
Dax
D
D000595:Amino Acid Sequence; D016950:Bordetella bronchiseptica / Q000378:metabolism*; D002104:Cadmium / Q000737:chemistry*; D027682:Cation Transport Proteins / Q000737:chemistry* / Q000378:metabolism*; D004563:Electrochemistry / Q000379:methods; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000737:chemistry; D007700:Kinetics; D013058:Mass Spectrometry / Q000379:methods; D008823:Micelles; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013696:Temperature; D015032:Zinc / Q000737:chemistry*
D027682:Cation Transport Proteins; D007477:Ions; D008823:Micelles; D002104:Cadmium; D015032:Zinc