Novel perspective into the interaction behavior study of the cyanidin with human serum albumin-holo transferrin complex: Spectroscopic, calorimetric and molecular modeling approaches

We examined the inducement of an interaction between two carrier proteins, human serum albumin (HSA) and human holo transferrin (HTF) within the presence of cyanidinin the form of binary and ternary systems, which was conducted by different spectroscopic, isothermal titration calorimetric (ITC), and molecular dynamics simulation techniques. The results of fluorescence spectroscopy verified the occurrence of this interaction by displaying the regular quenching of emission spectra of proteins as single and complex forms by cyanidin. Moreover, fluorescence emission suggested that, HSA-cyanidin, HTF-cyanidin and (HSA-HTF) cyanidin complexes follows an static mechanism with the binding constants of 8.81 × 104, 3.40 × 104, and 7.10 × 104 M−1, respectively, which were strongly reflected to moderate the affinity of cyanidin to both single and complex forms of proteins. The measured thermodynamic parameters obtained by ITC, determined the necessity of electrostatic forces for binding of cyanidin to HSA and HTF. Besides, obtaining a negative ΔG0 is indicative of spontaneous mode of binding process in both conditions. The different values of thermodynamic parameters of cyanidin binding to the forms of HSA, HTF and HSA-HTF complex clearly proved the similarity in the type of interaction forces between cyanidin and proteins as single and complex forms with various values. The observed changes in synchronous fluorescence results were related to the micro-environment properties of Tyr and Trp residues. The induced alternations in the secondary construction of both proteins were confirmed through the outcomes of quantitative analysis performed by circular dichroism spectroscopy (CD) techniques. FRET theory was exerted to calculate, the existing distance across the donor and acceptor, which were reported to be 1.85 nm, 1.97 nm, and 1.91 nm for the cases of HSA-cyanidin, HTF-cyanidin and (HSA-HTF) cyanidin complexes, respectively. Molecular displacement and protein–ligand docking simulations confirmed the binding of cyanidin to HSA and HTF through the binary and ternary systems.