Zinc to cadmium replacement in the prokaryotic zinc-finger domain

Abstract

Given the similar chemical properties of zinc and cadmium, zinc finger domains have been often proposed as mediators of the toxic and carcinogenic effects exerted by this xenobiotic metal. The effects of zinc replacement by cadmium in different eukaryotic zinc fingers have been reported. In the present work, to evaluate the effects of such substitution in the prokaryotic zinc finger, we report a detailed study of its functional and structural consequences on the Ros DNA binding domain (Ros87). We show that this protein, which bears important structural differences with respect to the eukaryotic domains, appears to structurally tolerate the zinc to cadmium substitution and the presence of cadmium does not affect the DNA binding activity of the protein. Moreover, we show for the first time how zinc to cadmium replacement can also take place in a cellular context. Our findings both complement and extend previous results obtained for different eukaryotic zinc fingers, suggesting that metal substitution in zinc fingers may be of relevance to the toxicity and/or carcinogenicity mechanisms of this metal.

The (unusual) aspartic acid in the metal coordination sphere of the prokaryotic zinc finger domain

“…Co(II)-apoRos87, Co(II)-apoRos87_ C27D and Co(II)-apoRos87_ C27D_G29K binding constants were determined in 30 mM HEPES and 100 mM NaCl at pH 7.4 by direct titration of the apo-protein solution (30 μM) with CoCl 2 solution (1.0 mM) up to 1.5 Co(II)/protein ratio. The absorbance at 340 nm indicative of the S − → Co(II) ligand-to-metal charge-transfer (LMCT) transition [46] was monitored and used to calculate the cobalt binding affinity constant [47][48][49]. To estimate the zinc binding affinity, the reverse titration experiment was carried out adding ZnCl 2 solution (1.0 mM) to Co(II)-Ros87, Co(II)-Ros87_C27D or Co(II)-Ros87_C27D_G29K complexes up to a Zn(II)/protein ratio of 2.5 and the collected data were fitted as previously reported [47].…”

Metal Exchange in the Interprotein ZnII‐Binding Site of the Rad50 Hook Domain: Structural Insights into CdII‐Induced DNA‐Repair Inhibition

“…The presented scientific problem of Zn II -to-Cd II substitution and its impact on zinc-binding proteins have been extensively studied;h owever,a ll published data are focused on intramolecular sites, mostly of zinc finger domains and metallothioneins. Effects of this substitution are not uniform and involven o, or very slight, changes in structure and function, like in the case of Sp1, [18] Tramtrack, [19] SUP37, [20] or Ros87, [21] as well as significant alterations of the domain fold, in the case of XPA, [5,22,23] p53, [24] or MTF-1. [25] Herein, we aim to illustrate for the first time how this phenomenon affects the intermolecular zinc-bindings ite by investigating Cd II binding to the central fragment of Pyrococcus furiosus (P. furiosus)R ad50 protein.…”

MucR binds multiple target sites in the promoter of its own gene and is a heat‐stable protein: Is MucR a H‐NS‐like protein?

“…MucR is a Ros/MucR protein family member and shares the conserved prokaryotic zinc‐finger domain with the other members of this protein family . The prokaryotic zinc‐finger domain is responsible for DNA‐binding of the protein Ros from Agrobacterium tumefaciens and the Ml proteins from Mesorhizobium loti . In A. tumefaciens , Ros represses the virulence gene expression , while the biological role of Ml proteins in M. loti has not been yet clarified.…”