Electrochemical characterization of Dps, a DNA-protecting protein

Dissertação para obtenção do Grau de Mestre em Biotecnologia

The objectives of the present work were the purification and electrochemical characterization of Dps and study its iron incorporation mechanism in the presence of hydrogen peroxide. A bacterial miniferritin (Dps) from Pseudomonas (Ps.) nautica 617 was expressed in BL21(DE3) E. coli cells transformed with pET21c(+)-1dps plasmid vector. Protein overexpression was performed in nutritionally rich LB medium containing 100 μg/mL ampicillin. Recombinant Dps was purified through a two-step process: weak ionic exchange chromatography (DEAE Sepharose Fast Flow XK 26/40 resin) and strong ionic exchange chromatography (Q Resource resin). Protein concentration was determined through UV/Visible spectroscopy. The electrochemical study was performed through cyclic voltammetry, square wave voltammetry and chronoamperometry; Dps was either in solution or adsorbed to the working electrode. The chosen supporting electrolyte was 200 mM MOPS pH 7.1 buffer with 200 mM NaCl. Electrochemical assays were performed in aerobic and anaerobic environment and in the presence of Dps and Fe(II) and H2O2, both of Dps co-substrates. For the different assays, working electrodes made of gold, glassy carbon and graphite were used with different results and conclusions. The iron incorporation in the ferroxidase centers and mineral core formation were studied. Assay results were obtained through direct electron transfer. Among the observed results, iron oxidation during protein incubation and oxygen production during the catalytic mechanism were observed. DNA-Dps interaction results were inconclusive, although some unconfirmed evidence exists of DNA protection by Dps from electrochemical oxidation.