Replacement of non-heme Fe(II) with Cu(II) in the α-ketoglutarate dependent DNA repair enzyme AlkB: Spectroscopic characterization of the active site

The bacterial DNA repair enzyme AlkB is an α-ketoglutarate (αKG) dependent non-heme Fe(II) containing dioxygenase. Here we describe, for the first time, the preparation of a Cu(II)-reconstituted form of AlkB in various complexes. Spectroscopic characterization showed correct AlkB folding upon incorporation of Cu(II) in the active site. The Cu site was classified as a type 2 site by EPR spectroscopy. The accessibility of the active site metal was studied using imidazole as a probe. Although addition of imidazole did not change the EPR spectrum of the AlkB-Cu-αKG complex, the spectrum of the AlkB-Cu-succinate complex clearly changed, indicating binding of imidazole at the Cu site. Binding of substrate (methylated DNA) to the AlkB-Cu-αKG complex did not induce changes in the EPR spectrum, demonstrating that the substrate does not bind in the immediate vicinity of the metal centre. This work provides a basis for advanced EPR approaches aimed at studying the interactions and dynamics of AlkB complexes in solution.