Acoustic cavitation enhances binding and compaction in methylene blue-bovine serum albumin complex

This study investigates the interaction mechanism between the sonosensitizer methylene blue (MB) and bovine serum albumin (BSA) and the impact of ultrasound on this complex, using multispectral techniques [fluorescence, ultraviolet-visible, and circular dichroism spectroscopy] coupled with computational simulations (molecular docking and dynamics). Spectroscopic experimental results indicate that MB binds to BSA at a single binding site with high affinity through hydrophobic interactions, and MB induces a conformational change in BSA, thereby improving BSA stability. This conclusion was verified by molecular docking analysis. Crucially, ultrasound exhibits multiple effects: it modifies the tertiary structure of BSA and degrades free MB, reducing its effective concentration, and it enhances MB-mediated fluorescence quenching of BSA and promotes structural compaction of BSA (increased α-helix content) only in the presence of MB. These indicate that ultrasound alters the interaction pattern between MB and BSA, while the presence of MB modifies the effect of ultrasound on the structure of BSA. These findings suggest potential bidirectional regulation under the specific in vitro conditions tested of drug-protein complexes by ultrasound, offering key insights for optimizing the efficacy of sonodynamic therapy and MB delivery strategies.