Exploring the binding behavior mechanism of vitamin B 12 to α-Casein and β-Casein: multi-spectroscopy and molecular dynamic approaches.

The aim of this study was to investigate the behavior interaction of α-Casein-B 12 and β-Casein-B 12 complexes as binary systems through the methods of multiple spectroscopic, zeta potential, calorimetric, and molecular dynamics (MD) simulation. Fluorescence spectroscopy denoted the role ofB 12 as a quencher in both cases of α-Casein and β-Casein fluorescence intensities, which also verifies the existence of interactions. The quenching constants of α-Casein-B 12 and β-Casein-B 12 complexes at 298 K in the first set of binding sites were 2.89 × 10 4 and 4.41 × 10 4 M -1 , while the constants of second set of binding sites were 8.56 × 10 4 and 1.58 × 10 5 M -1 , respectively. The data of synchronized fluorescence spectroscopy at Δλ = 60 nm were indicative of the closer location of β-Casein-B 12 complex to the Tyr residues. Additionally, the binding distance between B 12 and the Trp residues of α-Casein and β-Casein were obtained in accordance to the Förster's theory of nonradioactive energy transfer to be 1.95 nm and 1.85 nm, respectively. Relatively, the RLS results demonstrated the production of larger particles in both systems, while the outcomes of zeta potential confirmed the formation of α-Casein-B 12 and β-Casein-B 12 complexes and approved the existence of electrostatic interactions. We also evaluated the thermodynamic parameters by considering the fluorescence data at three varying temperatures. According to the nonlinear Stern-Volmer plots of α-Casein and β-Casein in the presence of B 12 in binary systems, the two sets of binding sites indicated the detection of two types of interaction behaviors. Time-resolved fluorescence results revealed that the fluorescence quenching of complexes are static mechanism. Furthermore, the outcomes of circular dichroism (CD) represented the occurrence of conformational changes in α-Casein and β-Casein upon their binding to B 12 as the binary system. The experimental results that were obtained throughout the binding of α-Casein-B 12 and β-Casein-B 12 complexes were confirmed by molecular modeling.Communicated by Ramaswamy H. Sarma.