Binding of Mammea A/AA (MA) to Plasma Proteins: UV-visible Spectroscopy and Molecular Dynamics Simulations Study

Mammea A/AA (MA) is the active compound of Mammea africana stem bark extract, exhibiting anticancer, antimicrobial, and antioxidant properties. To further prospect the usage of MA as a drug, its unusual ratiometric absorbance was exploited in this work to monitor its binding to plasma proteins. Bovine serum albumin (BSA) and human serum albumin (HSA) were considered as models of biological targets. From this process, the binding constant and thermodynamic parameters were evaluated. These binding parameters were similar to those obtained from the conventional fluorescence quenching, thus validating our approach. To further understand the difference of the binding parameters in BSA and HSA, accelerated molecular dynamics simulations for 60 ns were performed, using the restrained electrostatic potential procedure to derive realistic charge distribution on MA, which takes into account multipole contributions. This revealed that MA was bound to a site in the subdomain IB and surrounded by more charged and polar residues in HSA as compared to BSA, thus explaining the different solvatochromism observed for the two proteins. This study proves that MA as a drug can be transported by blood albumin. In addition, due to its ratiometric response in absorbance upon binding to a biological target, MA can be applied as a molecular probe to follow biomolecular interactions.