Interactions of an Artificial Zinc Finger Protein with Cd(II) and Hg(II): Competition and Metal and DNA Binding

Abstract

Cys2His2 zinc finger proteins are important for living organisms, as they—among other functions—specifically recognise DNA when Zn(II) is coordinated to the proteins, stabilising their ββα secondary structure. Therefore, competition with other metal ions may alter their original function. Toxic metal ions such as Cd(II) or Hg(II) might be especially dangerous because of their similar chemical properties to Zn(II). Most competition studies carried out so far have involved small zinc finger peptides. Therefore, we have investigated the interactions of toxic metal ions with a zinc finger proteins consisting of three finger units and the consequences on the DNA binding properties of the protein. Binding of one Cd(II) per finger subunit of the protein was shown by circular dichroism spectroscopy, fluorimetry and electrospray ionisation mass spectrometry. Cd(II) stabilised a similar secondary structure to that of the Zn(II)-bound protein but with a slightly lower affinity. In contrast, Hg(II) could displace Zn(II) quantitatively (logβ′ ≥ 16.7), demolishing the secondary structure, and further Hg(II) binding was also observed. Based on electrophoretic gel mobility shift assays, the Cd(II)-bound zinc finger protein could recognise the specific DNA target sequence similarly to the Zn(II)-loaded form but with a ~0.6 log units lower stability constant, while Hg(II) could destroy DNA binding completely.

DNA Interaction with Coordination Compounds of Cd(II)containing 1,10-Phenanthroline

“…It is known that cadmium ions when connected with sulfhydryl groups of enzymes may destroy their functions [19]. Cd(II) can replace Zn(II) in proteins [20]. Highly toxic cisplatin shows the most striking results in the treatment of various tumors.…”

Recent Progress in Coordination Chemistry

“…Gyurcsik et al studied the solution chemistry of Cd(II) and Hg(II) cations as competitors of Zn(II) in a specific artificial zinc-finger protein and found them to have surprisingly different behaviors [6].…”