Structure 2008-09-10

Insights into the mode of action of a putative zinc transporter CzrB in Thermus thermophilus.

Vadim Cherezov, Nicole Höfer, Doletha M E Szebenyi, Olga Kolaj, J Gerard Wall, Richard Gillilan, Vasundara Srinivasan, Christopher P Jaroniec, Martin Caffrey

Index: Structure 16(9) , 1378-88, (2008)

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Abstract

The crystal structures of the cytoplasmic domain of the putative zinc transporter CzrB in the apo and zinc-bound forms reported herein are consistent with the protein functioning in vivo as a homodimer. NMR, X-ray scattering, and size-exclusion chromatography provide support for dimer formation. Full-length variants of CzrB in the apo and zinc-loaded states were generated by homology modeling with the Zn2+/H+ antiporter YiiP. The model suggests a way in which zinc binding to the cytoplasmic fragment creates a docking site to which a metallochaperone can bind for delivery and transport of its zinc cargo. Because the cytoplasmic domain may exist in the cell as an independent, soluble protein, a proposal is advanced that it functions as a metallochaperone and that it regulates the zinc-transporting activity of the full-length protein. The latter requires that zinc binding becomes uncoupled from the creation of a metallochaperone-docking site on CzrB.