In vitro and in silico insights into the molecular interaction mechanism of acetylshikonin with bovine serum albumin

Acetylshikonin (ASK), as a privileged naphthoquinone derivative with unique spectroscopic properties, is considered an effective substance in biomedical areas. This manuscript was purposefully undertaken for systematic characterization of ASK-bovine serum albumin (BSA) binding to best understand the pharmaceutics properties of ligand, and deep illustration of conformational changes of BSA on the addition of ASK. The overall results of surface plasmon resonance (SPR) and fluorescence spectroscopy indicated temperature dependence of binding constant attributes. Further, thermodynamic analysis on the BSA-ASK interaction (ΔG = –23 kJ, ΔH = 215 kJ, and ΔS = 803 J) unraveled viable, hydrophobic and hydrogen bonds in moderate-affinity complex formation (k_b of 10⁴ M⁻¹). Circular dichroism (CD) spectroscopy suggested the addition of ASK leads to secondary structure changes of BSA, by increasing α-helixes content. In addition, atomic force microscopy (AFM) and dynamic light scattering (DLS) techniques showed that ASK causes slight conformational shrinkage, by coalescing BSA to form large particles. Molecular modeling showed the flexibility of the hydrophobic pocket between subdomains IIA and IIB induced an allosteric modulation in BSA structure, thereby localizing itself in the proximity of the tryptophan (Trp-213) residue. Taken together, the results of ASK-BSA interaction can be of great importance for expanding the bio-applications of shikonin.