Fluorescence resonance energy transfer by α-helical coiled coil polypeptides in response to metal ions

The fluorescence resonance energy transfer (FRET) in response to Ni2+ ions in a pH 7.0 Tris–HCl buffer solution was investigated for the α-helical coiled coil polypeptides (Pep5 and Pep6) with both histidine residues as a metal binding site and energy donor/acceptor residues. The secondary structure of the polypeptides was examined by means of circular dichroism (CD) spectroscopy. The CD measurements showed that the polypeptides underwent the conformational change from random to hetero-block α-helical coiled coils, (Pep5)3–Ni2+–(Pep6)3 by addition of Ni2+ ions. Furthermore, in the presence of Ni2+ ions the FRET occurred between donor and acceptor residues affixed to the Pep5 and Pep6, respectively. It was made clear that the conformational change of polypeptides caused by coordination of metal ions brings about the FRET.