A Tetra-Nuclear Iron Complex That Can Promote Both DNA And Protein Hydrolysis

DNA and protein hydrolysis promoted by di- and multi-nuclear metal complexes is of increasing importance in biotechnology and medicine. Many natural hydrolases are activated by two and more metal ions. Both DNA and protein cleavage by multi-nuclear iron complexes via hydrolytic pathway was investigated here in order to give insight into the cooperativity between or among metals and to obtain a novel probe which can get the structural information of biomacromolecules.The tetranuclear trivalent iron complex [Fe4(NTB)4(μ-O)2(μ4-Suc)]6+ can promote pBR322 DNA hydrolysis in pH<7 acetate buffer, confirmed by anaerobic reactions and free radical quenching. The addition of phosphate can inhibit this reactivity. The reason may be that the phosphate can interfere the coordination interactions between the ferric ions and the phosphate groups from DNA. The kinetic profiles obtained by densitometric quantification of the agarose gels were analyzed using two simplified kinetic model. The fitting of the kinetic data is in good agreement with the model of tandem reactions. The conversion rates from form I to form II increases with the concentration of the complex showing a concentration-dependent saturation behavior. The fitting of the data by the Michaelis-Menten equation gives ksat=0.014 min-1, KM=7.4 X 10-6 mol L-1. The binding constant Kb=5.9 X 105 mol-1 L obtained through DNAtitration shows a strong affinity of [Fe4(NTB)4(μ-O)2(μ4-Suc)]6+ to DNA. It can be inferred from spectra data that the μ-oxo bridge in the complex can be protonated to hydroxide anion as a nucleophile to attack the phosphorus atom of DNA.On the other hand, we explored the interactions between the tetra-iron complex and the proteins comprising different secondary structures. The data reveal that the complex can effectively promote bovine serum albumin(BSA) hydrolysis which mainly comprises alpha-helix. However, in the case of superoxide dismutase(SOD) that contains a p-barrel structure, the complex does not show the hydrolytic activity. As to lysozyme that comprises a-helix lobe and (3-sheet respectively, the hydrolysis efficiency is higher than that for SOD, but less than that for BSA. The rate constant is 0.016 h-1 for BSA and 0.0022 h-1 for lysozyme, respectively. These results demonstrate that the tetranuclearcomplex is capable of basically recognizing and degrading proteins with different secondary structures. Protein degradation by di-nuclear complex [Fe2(DTPB)(μ-O)(μ-OAc)]2+ was also assayed. The results show that the complex can only hydrolyze BSA with the rate constant of k=0.0079 h-1.