Study on the zinc ions binding to human lactoferrin

Abstract

The article presents the results of the study of Zn2+ binding to recombinant human lactoferrin. Isotherm studies were utilized with subsequent fit to Langmuir, Freundlich, and Henry models. Moreover, the kinetics of the process was investigated with the use of pseudo-first, pseudo-second, and Weber-Morris models for the process description. The study results revealed the complex nature of Zn2+ binding to lactoferrin, where based on isotherm three different sorption steps can be distinguished. Based on isotherm three different concentrations of Zn2+ solution (60, 300, and 600 mg/L) were chosen for Zn-lactoferrin complexes synthesis for further investigations. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis, transmission electron microscopy, inductively coupled plasma mass spectrometry, Fourier-transform infrared and Raman spectroscopies were utilized which enabled the description of the Zn-binding process in a more accurate way. As a result, the highest Zn2+ content (7.92 mg/g) was observed for the complex synthesized with 600 mg/L Zn2+ solution. Spectroscopic studies reveal that the zinc ions binding may occur through the deprotonated carboxylic groups of aspartic and glutamic acids, imidazole ring of a histidine, or –CN and –OH groups of other amino acids as well as through weak noncovalent cation–π interactions. According to obtained results, it is also can be suggested that high Zn2+ concentration can lead to changes in protein structure and partial loss of Fe3+ from the metal-binding clefts. The obtained lab results were also complemented with Molecular Dynamics and Density Functional Theory simulations that support the conclusions outlined from lab experiments.