Expression and purification of a recombinant DNA-binding domain of ADR6 protein from Escherichia coli and its secondary structure characterization

From Saccharomyces cerevisiae, a piece of ADR6 gene that encodes a DNA-bind ing domain of ADR6 protein was cloned and expressed in Escherichia coli. Wi th Ni-chelating column and high-performance liquid chromatography (HPLC), T his recombinant protein (RDB-ADR6) could reach more than 95% purity. The mo lecular weight (MW) of RDB-ADR6 is 13405 Da with mass spectra technique con taining 114 amino acid residues. Structural aspects of RDB-ADR6 were examin ed by spectroscopic techniques. It contains approximately 25% alpha-helix a nd 24% alpha-turn both with circular dichroism (CD) and Fourier transform i nfrared spectroscopy (FTIR). Percent of beta-sheet differs between these tw o methods in that 22% in CD while 35% in FTIR. RDB-ADR6 contains only one t ryptophan residue. Fluorescence studies show that this residue may lie in a hydrophobic circumstance either on or near the surface of the molecule. Th is was confirmed by a blue shift of 20 nm in the fluorescence emission spec trum as compared to the protein in 6 M guanidine hydrochloride (GuHCl) and by quenching studies with KI. Effects of different pH and SDS in different concentration on the secondary structure of RDB-ADR6 were also studied. A m odel was obtained by comparative modeling with homologous known structure p rotein by program Modeller 4. (C) 2000 Elsevier Science B.V. All rights res erved.