Understanding the binding between Rosmarinic acid and serum albumin: In vitro and in silico insight

Rosmarinic acid (RA) is a natural product that is increasingly being used in food industries and cosmetic industries. Drug pharmacokinetics is affected upon binding with protein, thus making drug-protein interactions imperative to study. The binding affinity between RA and serum albumin, human serum albumin (HSA) was investigated using multi spectroscopic approaches and in silico analysis. UV–vis, fluorescence, and circular dichroism (CD) spectroscopies were employed to elucidate the mode and the mechanism of HSA-RA interaction. Fluorescence studies showed excellent binding between HSA and RA with a binding constant (K) of 10⁷ M⁻¹. Fluorescence quenching experiments carried out at three different temperatures suggested that HSA-RA complex formation is guided by static quenching. The binding constants were found to decrease at higher temperatures suggesting the formation of the less stable complex at higher temperatures. Far UV-CD spectra revealed slight alterations in the secondary structure of HSA upon RA binding further validating complex formation between HSA and RA. Thermodynamic parameters obtained suggested hydrophobic interactions to play a dominant role in this interaction. Isothermal titration calorimetry (ITC) further validated the spontaneous and exothermic nature of this reaction. Molecular docking study shows that RA is binding with appreciable affinity showing specific interactions towards the binding pocket residues of HSA mimicking the binding pose of co-crystallized myristic acid. Molecular dynamics simulation study suggested that RA is stabilizing the HSA structure and leads to fewer conformational changes upon binding.