Binding of terbium to apoferritin: a fluorescence study

Area of Science:

• Biochemistry
• Biophysical Chemistry
• Metalloprotein Research

Background:

• Apoferritin is a protein shell that stores iron.
• Understanding metal ion binding to apoferritin is crucial for elucidating iron storage mechanisms.
• Terbium (Tb(III)) is a lanthanide ion with potential applications in biological imaging and therapeutics.

Purpose of the Study:

• To investigate the binding of terbium (Tb(III)) to apoferritin.
• To determine if iron (Fe(II)) competes with Tb(III) for apoferritin binding sites.
• To explore the molecular basis of Tb(III)-induced inhibition of iron incorporation into apoferritin.

Main Methods:

• Luminescence spectroscopy was employed to quantify Tb(III) binding.
• Crystallographic data was used for structural validation.
• Competition assays were performed to assess the interaction between Fe(II) and Tb(III) binding sites.

Main Results:

• Apoferritin binds three Tb(III) atoms per subunit, consistent with crystallographic findings.
• Fe(II) competes with Tb(III) for at least some of the identified binding sites.
• Calcium (Ca(II)) does not compete with Tb(III) for binding to apoferritin, unlike in other Ca(II)-binding proteins.

Conclusions:

• The binding stoichiometry of Tb(III) to apoferritin has been established.
• Metal ion competition at binding sites provides a molecular explanation for Tb(III) inhibition of iron uptake.
• Tb(III) exhibits distinct binding behavior compared to Ca(II) in apoferritin.