Glycoproteomics meets thermodynamics: A calorimetric study of the effect of sialylation and synergistic anion on the binding of iron to human serum transferrin

The thermodynamic parameters for the binding of ferric ions to human serum transferrin (hTf) as the major mediator of iron transport in blood plasma were determined by isothermal titration calorimetry in the presence of carbonate and oxalate as synergistic anions at pH 7.4. The results indicate that the binding of ferric ions to the two binding sites of hTf is driven both enthalpically and entropically in a lobe-dependent manner: binding to the C-site is mainly enthalpically driven, whereas binding to the N-site is mainly entropically driven. Lower sialic acid content of hTf leads to more exothermic apparent binding enthalpies for both lobes, while the increased apparent binding constants for both sites were found in the presence of carbonate. Sialylation also unequally affected the heat change rates for both sites only in the presence of carbonate, but not in the presence of oxalate. Overall, the results suggest that the desialylated hTf has a higher iron sequestering ability, which may have implications for iron metabolism.

Automated summary

The thermodynamic parameters of ferric ions binding to human serum transferrin (hTf) were determined in the presence of carbonate and oxalate. The results indicate that the binding of ferric ions to hTf is driven by both enthalpy and entropy, with different contributions from different binding sites. Lower sialic acid content in hTf leads to stronger binding enthalpies, while the presence of carbonate increases the apparent binding constants. Sialylation also affects the heat change rates for binding sites, but only in the presence of carbonate.