A comparison study of the interaction between ß-lactoglobulin and retinol at two different conditions: spectroscopic and molecular modeling approaches.

The interaction between bovin ß-Lactoglobulin (ß-LG) and retinol at two different pH values was investigated by multispectroscopic, zeta potential, molecular modeling, and conductometry measurements. The steady state and polarization fluorescence spectroscopy revealed that complex formation at two different pH values could occur through a remarkable static quenching. According to fluorescence quenching, one set of binding site at pH 2 and two sets of binding sites at pH 7 were introduced for binding of retinol to ß-LG that show the enhancement of saturation score of ß-LG to retinol in dimmer condition. The polarization fluorescence analysis represented that there is more affinity between ß-LG and retinol at pH 7 rather than at pH 2. The effect of retinol on ß-LG was studied by UV-visible, circular dichroism (CD), and synchronous fluorescence, which indicated that retinol induced more structural changes on ß-LG at pH 7. ß-LG-retinol complex formation at two different pH values was recorded via applying resonance light scattering (RLS) and zeta potential. Conductometry and RLS showed two different behaviors of interaction between ß-LG and retinol at two different pH values; therefore, dimmer formation played important roles in different behaviors of interaction between ß-LG and retinol. The zeta potential was the implied combination of electrostatic and hydrophobic forces which are involved in ß-LG-retinol complex at two different pH values, and the hydrophobic interactions play a dominant role in complex formation. Molecular modeling was approved by all experimental results. The acquired results suggested that monomer and dimmer states of ß-LG can be induced by retinol with different behaviors.

Binding site identification of metformin to human serum albumin and glycated human serum albumin by spectroscopic and molecular modeling techniques: a comparison study.

The interaction between metformin and human serum albumin (HSA), as well as its glycated form (gHSA) was investigated by multiple spectroscopic techniques, zeta potential, and molecular modeling under physiological conditions. The steady state and time-resolved fluorescence data displayed the quenching mechanism of HSA-metformin and gHSA-metformin was static. The binding information, including the binding constants, number of binding sites, effective quenching constant showed that the binding affinity of metformin to HSA was greater than to gHSA which also confirmed by anisotropy measurements. It was determined that metformin had two and one set of binding sites on HSA and gHSA, respectively. Far-UV CD spectra of proteins demonstrated that the α-helical content decreased with increasing metformin concentration. The zeta potential and resonance light scattering (RLS) diagrams provided that lower drug concentration induced metformin aggregation on gHSA surface as compare to HSA. The increase in polarizability was one of the important factors for the enhancement of RLS and the formation of drug/protein complexes. The zeta potential results suggested that both hydrophobic and electrostatic interactions played important roles in the protein-metformin complex formation. Site marker experiments and molecular modeling showed that the metformin bound to subdomain IIIA (Sudlow's site II) on HSA and gHSA.