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Tertiary structural changes and iron release from human serum transferrin
S L Mecklenburg1, R J Donohoe, G A Olah
1Biochemistry and Biotechnology Group, CST-4, MS-J586, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
Journal of Molecular Biology
|August 1, 1997
Summary
Iron release from human serum transferrin was studied using spectroscopy and X-ray scattering. Iron is released from the N-lobe first, followed by structural changes in the protein.
Area of Science:
- Biochemistry
- Structural Biology
- Biophysics
Background:
- Human serum transferrin (hTf) is crucial for iron transport in blood.
- Understanding iron release mechanisms is key to various physiological processes.
Purpose of the Study:
- To investigate the pH-dependent iron release from human serum transferrin.
- To correlate iron release with structural changes using spectroscopy and small-angle X-ray scattering (SAXS).
Main Methods:
- Spectroscopic measurement of bound iron via charge transfer absorption band intensity.
- Small-angle solution X-ray scattering (SAXS) to determine structural parameters like radius of gyration (Rg).
- Equilibrated samples across a pH range (5.69–7.77) in phosphate buffers.
Main Results:
- An empirical pK of 6.9 for iron release was observed, with N-lobe release nearly complete by pH 7.0.
- Radius of gyration (Rg) remained constant during N-lobe iron release but increased at lower pH.
- Radius of gyration of cross-section (Rc) increased during N-lobe iron release, suggesting specific domain rotations.
Conclusions:
- Iron release from hTf is a stepwise process, initiated at the N-lobe.
- Specific domain movements within the N-lobe occur during iron release, independent of overall protein expansion.
- C-lobe domain rotation contributes to structural changes at lower pH, but cannot fully explain observed Rg increases.
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