Article

Insights into the Mode of Action of a Putative Zinc Transporter CzrB in Thermus thermophilus

Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
Structure (Impact Factor: 6.79). 10/2008; 16(9):1378-88. DOI: 10.1016/j.str.2008.05.014
Source: PubMed

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.

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    • "These include charge repulsion between the two monomers and attraction via a hydrophobic interaction at the center of the internal dimerization interface, pulling the monomers closer [20]. MamM and CzrB CTD dimers exhibited a conformational change toward a tighter V-shaped dimer upon zinc binding that is considered to be associated with transport activation and regulation [19], [20]. The dimerization interface was shown to be highly significant to the CDF transport activity as the introduction of a mutation into the dimerization interface of MamM did not alter dimer formation but rather abolished the in vivo transport activity [20]. "
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    • "Despite the relatively low sequence homology in the cytoplasmic domains, the structural homology between them is impressive. For example, the αββα structural core of the C-terminal domain from α1 to α2 of the E. coli zinc transporter YiiP can be superimposed onto the equivalent portion of human copper metallochaperone Hah1 with a root mean square deviation of 1.8 Å for 42 common Cα positions, although there is no sequence homology between the C-terminal domain and Hah1 after a evolutionary period of more than thousand millions of years [[19], see ref. [21]], while the soluble fragment from Thermus thermophilus zinc transporter CzrB overlays the cytoplasmic domain of YiiP with a Cα-root mean square deviation of 1.8 Å over 79 residues with an overall sequence identity of 8.8% [20]. "
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