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

• Published in: Journal of inorganic biochemistry 2023-07, Vol.244, p.112207-112207, Article 112207
• Main Authors: Borko, Valentina, Friganović, Tomislav, Weitner, Tin
• Format: Article
• Language: English
• Subjects: Anions - chemistry; Calorimetry; Carbonates; Glycoproteomics; Human serum transferrin; Humans; Iron - chemistry; Isothermal titration calorimetry; Oxalates; Sialic acid; Synergistic anion; Thermodynamics; Transferrin - metabolism
• ISSN: 0162-0134; 1873-3344
• DOI: 10.1016/j.jinorgbio.2023.112207

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. Considering that glycan modifications of intracellular and extracellular proteins play a crucial role in almost all biological processes, the importance of glycan heterogeneity of human serum transferrin for its basic function of iron transport was investigated using isothermal titration calorimetry, a powerful technique for estimating thermodynamic parameters in a single experiment. [Display omitted] •Lower sialic acid content results in more exothermic binding for both sites.•Nature of synergistic anion modulates the effect of desialylation on thermodynamics.•Rates of heat change can be estimated from the weighted width of the integrated ITC peaks.•Weaker prebinding of carbonate increases the effect of desialylation on the observed rates.