Structural characteristics and thermal stabilities of bovine, caprine and ovine lactoferrins with different iron saturation levels

This study demonstrated the purification of bovine lactoferrin (BLF), caprine lactoferrin (CLF) and ovine lactoferrin (OLF) by ion-exchange chromatography and gel filtration chromatography. The purified lactoferrin (LF) were identified by mass spectrometry and its purity was analyzed by RP-HPLC. LFs with different iron saturations were established, and it was found that iron saturation of Holo-CLF (62.01%) and Holo-OLF (63.74%) were lower than Holo-BLF (83.93%). The effect of iron saturation on the physicochemical properties of LFs were evaluated by circular dichroism, Fourier transform infrared spectroscopy and differential scanning calorimetry. The results showed that both species and iron saturation did not affect the secondary structure of LFs, however, they did influence tertiary structure of LFs. The conformation of Holo-LFs was more compact than that of Apo-LFs. Furthermore, Native-OLF showed the tightest conformation, followed by Native-BLF and Native-CLF. In addition, the increase of iron saturation enhanced the thermal stability of LFs in all three species. Among three species, Apo-OLF was the most thermally stable in among three species due to its more compact structure, while Holo-BLF was the most thermally stable among three species due to its highest iron saturation. Although Native-CLF had a relatively lower iron saturation compared to BLF and OLF, its thermal stability was relatively higher as the main denaturation temperature peak of CLF was located at 85.65 °C. These findings would contribute to further understanding of the information of LFs at different iron saturation levels, which is crucial for the production and application of LFs in the future.