@article {46408,
	title = {Structural basis of the metal specificity for nickel regulatory protein NikR.},
	journal = {Biochemistry},
	volume = {47},
	year = {2008},
	month = {2008 Feb 19},
	pages = {1938-46},
	abstract = {<p>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 Ni2+, including Co2+, Cu2+, Zn2+, and Cd2+. 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{\textquoteright}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 Cu2+ and Zn2+ ions and compared them with the previously published structures with Ni2+. We observe that Cu2+ ions bind in a manner very similar to that of Ni2+, with a square planar geometry but with longer bond lengths. Crystals grown in the presence of Zn2+ reveal a protein structure similar to that of apo MBD with a disordered alpha3 helix, but with two electron density peaks near the Ni2+ binding site corresponding to two Zn2+ ions. These structural findings along with biochemical data on NikR support a hypothesis that ordering of the alpha3 helix is important for repressor activation.</p>
},
	keywords = {Binding Sites, Circular Dichroism, Escherichia coli Proteins, Metals, Models, Molecular, Protein Conformation, Repressor Proteins},
	issn = {0006-2960},
	doi = {10.1021/bi702006h},
	author = {Phillips, Christine M and Schreiter, Eric R and Guo, Yayi and Wang, Sheila C and Zamble, Deborah B and Drennan, Catherine L}
}
@article {46400,
	title = {Crystal structure of the nickel-responsive transcription factor NikR.},
	journal = {Nature Structural Biology},
	volume = {10},
	year = {2003},
	month = {2003 Oct},
	pages = {794-9},
	abstract = {<p>NikR is a metal-responsive transcription factor that controls nickel uptake in Escherichia coli by regulating expression of a nickel-specific ATP-binding cassette (ABC) transporter. We have determined the first two structures of NikR: the full-length apo repressor at a resolution of 2.3 A and the nickel-bound C-terminal regulatory domain at a resolution of 1.4 A. NikR is the only known metal-responsive member of the ribbon-helix-helix family of transcription factors, and its structure has a quaternary arrangement consisting of two dimeric DNA-binding domains separated by a tetrameric regulatory domain that binds nickel. The position of the C-terminal regulatory domain enforces a large spacing between the contacts that each NikR DNA-binding domain can make with the nik operator. The regulatory domain of NikR contains four nickel-binding sites at the tetramer interface, each exhibiting a novel square-planar coordination by three histidines and one cysteine side chain.</p>
},
	keywords = {Amino Acid Sequence, Crystallography, X-Ray, Escherichia coli, Escherichia coli Proteins, Molecular Sequence Data, Nickel, Protein Structure, Tertiary, Repressor Proteins},
	issn = {1072-8368},
	doi = {10.1038/nsb985},
	author = {Schreiter, Eric R and Sintchak, Michael D and Guo, Yayi and Chivers, Peter T and Sauer, Robert T and Drennan, Catherine L}
}
