Structural Basis of the Metal Specificity for Nickel Regulatory Protein NikR
In the presence of excess nickel, Escherichia coli NikR regulates cellular nickel uptake by suppressing the transcription of the nik operon, which encodes the nickel uptake transporter, NikABCDE. Previously published in vitro studies have shown that NikR is capable of binding a range of divalent transition metal ions in addition to Ni{sup 2+}, including Co{sup 2+}, Cu{sup 2+}, Zn{sup 2+}, and Cd{sup 2+}. To understand how the high-affinity nickel binding site of NikR is able to accommodate these other metal ions, and to improve our understanding of NikR's mechanism of binding to DNA, we have determined structures of the metal-binding domain (MBD) of NikR in the apo form and in complex with Cu{sup 2+} and Zn{sup 2+} ions and compared them with the previously published structures with Ni{sup 2+}. We observe that Cu{sup 2+} ions bind in a manner very similar to that of Ni{sup 2+}, with a square planar geometry but with longer bond lengths. Crystals grown in the presence of Zn{sup 2+} reveal a protein structure similar to that of apo MBD with a disordered {alpha}3 helix, but with two electron density peaks near the Ni{sup 2+} binding site corresponding to two Zn{sup 2+} ions. These structural findings along with biochemical data on NikR support a hypothesis that ordering of the {alpha}3 helix is important for repressor activation.
- Research Organization:
- Stanford Linear Accelerator Center (SLAC)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC02-76SF00515
- OSTI ID:
- 953045
- Report Number(s):
- SLAC-REPRINT-2009-239
- Journal Information:
- Biochem. 47:1938,2008, Journal Name: Biochem. 47:1938,2008 Journal Issue: 7 Vol. 47
- Country of Publication:
- United States
- Language:
- English
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