Nickel-Specific Response in the Transcriptional Regulator, Escherichia coli NikR
Studies of the transcriptional repression of the Ni-specific permease encoded by the P{sub nik} operon by Escherichia coli NikR using a LacZ reporter assay establish that the NikR response is specific to nickel in vivo. Toward understanding this metal ion-specific response, X-ray absorption spectroscopy (XAS) analysis of various M-NikR complexes (M = Co(II), Ni(II), Cu(II), Cu(I), and Zn(II)) was used to show that each high-affinity binding site metal adopts a unique structure, with Ni(II) and Cu(II) being the only two metal ions to feature planar four-coordinate complexes. The results are consistent with an allosteric mechanism whereby the geometry and ligand selection of the metal present in the high-affinity site induce a unique conformation in NikR that subsequently influences DNA binding. The influence of the high-affinity metal on protein structure was examined using hydrogen/deuterium (H/D) exchange detected by liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS). Each NikR complex gives rise to differing amounts of H/D exchange; Zn(II)- and Co(II)-NikR are most like apo-NikR, while the exchange time course is substantially different for Ni(II) and to a lesser extent for Cu(II). In addition to the high-affinity metal binding site, E. coli NikR has a low-affinity metal-binding site that affects DNA binding affinity. We have characterized this low-affinity site using XAS in heterobimetallic complexes of NikR. When Cu(II) occupies the high-affinity site and Ni(II) occupies the low-affinity site, the Ni K-edge XAS spectra show that the Ni site is composed of six N/O-donors. A similar low-affinity site structure is found for the NikR complex when Co(II) occupies the low-affinity site and Ni(II) occupies the high-affinity site, except that one of the Co(II) ligands is a chloride derived from the buffer.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 930361
- Report Number(s):
- BNL-81080-2008-JA; JACSAT; TRN: US200904%%651
- Journal Information:
- Journal of the American Chemical Society, Vol. 129; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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