Spectroscopic studies of the interaction of aluminum(III) with transferrins

In this review, we summarize the spectroscopic techniques used to examine the binding of aluminum to the transferrins, a class of vertebrate iron-binding proteins. Interest in the binding of Al3+ by the transferrins, in particular serum transferrin, stems from the suggested role of metal detoxification in plasma by this protein and the association of this metal ion in human disorders such as Alzheimer's disease. A number of indirect methods of observing the binding of Al3+ to the transferrins, such as UV-visible spectroscopy, X-ray solution scattering, and H-1 and C-13 nuclear magnetic resonance(NMR) spectroscopy, have revealed information on the coordination and structure of the metal ion binding sites as well as conformational changes that occur on the binding of metal ions. Various NMR approaches, including Al-27 NMR, have elucidated subtle differences within the binding sites and between several transferrins. Most notably, the recent detection of transferrin-bound Al-27 NMR signals, characteristic of quadrupolar relaxation in the limit of slow molecular motion, has allowed us to observe directly the metal ion bound to the protein.