Binding interactions between ar-turmerone and human serum albumin: mechanistic and biophysical insights

Ar-turmerone, a major bioactive compound in <i>Curcuma purpurascens</i>, has been reported to exhibit anti-inflammatory, antiproliferative, antifungal, antioxidant, and anticancer properties. This study investigated its interaction with human serum albumin (HSA) using spectroscopic, microscopic, and computational approaches to characterize its binding properties, which are crucial for its distribution and transport in the bloodstream. Fluorescence spectroscopy showed a 34% decrease in HSA fluorescence intensity at 90 μM ar-turmerone, accompanied by a 2 nm blue shift, suggesting a transition of the protein's fluorophores' microenvironment to a slightly nonpolar state. Binding analysis indicated a moderate binding affinity (<i>K</i>_a = 1.79 ± 0.12 × 10⁴ M^-1) and a negative Gibbs free energy change (ΔG° = -6.03 ± 0.04 kcal/mol), indicating a spontaneous and energetically favorable binding process. Hypochromic effects near the Trp residue suggested a static interaction mechanism. Circular dichroism analysis confirmed that ar-turmerone did not induce major alterations in HSA's secondary and tertiary structures. Microscopic observations revealed slight modifications to the protein surface, suggesting the formation of protein aggregates. Both displacement studies and molecular docking results indicated that ar-turmerone primarily binds at the Site III (subdomain IB) of HSA. Molecular docking further suggested that this binding is stabilized through hydrogen bonding, hydrophobic interactions, and van der Waals forces. These findings provide insights into the binding dynamics of ar-turmerone with HSA, which may influence its transport, stability, and bioavailability. Understanding this interaction is essential for assessing its pharmacokinetic behavior, including transport, stability, bioavailability, which are critical for potential applications in drug delivery and therapeutic development.