On/off resonance Raman optical activity of human serum transferrin

Abstract

AbstractThe transferrin proteins exhibit two high affinity Fe(III) binding pockets and are responsible for the iron transport into cells of higher order organisms. Previously, transferrins have been studied as possible transporter molecules for drugs delivery. In this study, Raman optical activity (ROA) was employed to investigate human serum transferrin. Due to the presence of Fe(III) in the holo form of the protein, it is in resonance with the the laser excitation wavelength (of 532 nm) used in the experiments. Consequently, resonance enhanced ROA bands were observed in the spectrum of the holo form. Nevertheless, far from resonance bands, arising from the protein backbone, could simultaneously be observed in the ROA spectrum of the holo form. This implies that ROA can be used to provide simultaneously information on the metal binding pocket as well as on the secondary structure of the protein. Furthermore, it was found that the amount of observed resonance enhanced ROA signals can be tuned by partially removing the iron present in the protein. Electronic circular dichroism (ECD) was employed to verify the Raman/ROA results.