Interaction of a dirhamnolipid biosurfactant with sarcoplasmic reticulum calcium ATPase (SERCA1a)

The interaction of a dirhamnolipid biosurfactant secreted by Pseudomonas aeruginosa with calcium ATPase from sarcoplasmic reticulum (SR) was studied by means of different approaches, such as enzyme activity, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and molecular docking simulations. The ATP hydrolysis activity was fully inhibited by incubation with dirhamnolipid (diRL) up to 0.1 mM concentration, corresponding to a surfactant concentration below membrane solubilization threshold. Surfactant-protein interaction induced conformational changes in the protein observed by an increase in the accessibility of tryptophan residues to the aqueous phase and by changes in the secondary structure of the protein as seen by fluorescence and FTIR spectroscopy. As a consequence, the protein become more unstable and denatured at lower temperatures, as seen by enzyme activity and DSC studies. Finally, these results were explained at molecular level throughout molecular docking simulations. It is concluded that there is a specific dirhamnolipid-protein interaction not related to the surface activity of the surfactant but to the particular physicochemical properties of the biosurfactant molecule.