Specific DNA-protein interactions are vital for cellular life maintenance processes, such as transcriptional regulation, chromosome maintenance, replication and DNA repair, and their monitoring gives valuable information on molecular-level organization of those processes. Here, we propose a new method of label-free electrochemical sensing of sequence specific binding between the lysozyme protein and a single stranded DNA aptamer specific for lysozyme (DNAapta) that exploits the constant current chronopotentiometric stripping (CPS) analysis at modified mercury electrodes. Specific lysozyme-DNAapta binding was distinguished from nonspecific lysozyme-DNA interactions at thioglycolic acid-modified mercury electrodes, but not at the dithiothreitol-modified or bare mercury electrodes. Stability of the surface-attached lysozyme-DNAapta layer depended on the stripping current (Istr) intensity, suggesting that the integrity of the layer critically depends on the time of its exposure to negative potentials. Stabilities of different lysozyme-DNA complexes at the negatively polarized electrode surface were tested, and it was shown that structural transitions of the specific lysozyme-DNAapta complexes occur in the Istr ranges different from those observed for assemblies of lysozyme with DNA sequences capable of only nonspecific lysozyme-DNA interactions. Thus, the CPS allows distinct discrimination between specific and non-specific protein-DNA binding and provides valuable information on stability of the nucleic acid-protein interactions at the polarized interfaces.

Institute of Biophysics The Czech Academy of Science v v i Královopolská 135 61265 Brno Czech Republic

Interdisciplinary Nanoscience Center Science and Technology Aarhus University Gustav Wieds Vej 14 DK 8000 Aarhus C Denmark

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Electrochemistry in sensing of molecular interactions of proteins and their behavior in an electric field