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Biosurfactant–Protein Interaction: Influences of Mannosylerythritol Lipids-A on β-Glucosidase

Fan, Linlin, Xie, Pujun, Wang, Ying, Huang, Zisu, Zhou, Jianzhong
Journal of agricultural and food chemistry 2018 v.66 no.1 pp. 238-246
amino acids, beta-glucosidase, biosurfactants, circular dichroism spectroscopy, differential scanning calorimetry, enthalpy, enzyme activity, enzyme inhibition, fatty acids, hydrogen bonding, hydrophobic bonding, micelles, temperature, titration
In this work, the influences of a biosurfactant, mannosylerythritol lipids-A (MEL-A) toward β-glucosidase activity and their molecular interactions were studied by using differential scanning calorimetry (DSC), circular dichroism spectroscopy (CD), isothermal titration calorimetry (ITC), and docking simulation. The enzyme inhibition kinetics data showed that MEL-A at a low concentration (< critical micelle concentration (CMC), 20.0 ± 5.0 μM) enhanced β-glucosidase activity, whereas it inhibited the enzyme activity at higher concentrations more than 20.0 μM, followed by a decreased Vₘₐₓ and Kₘ of β-glucosidase. The thermodynamics and structural data demonstrated that the midpoint temperature (Tₘ) and unfolding enthalpy (ΔH) of β-glucosidase was shifted to high values (76.6 °C, 126.3 J/g) in the presence of MEL-A, and the secondary structure changes of β-glucosidase, including the increased α-helix, β-turn, or random coil contents, and a decreased β-sheet content were caused by MEL-A at a CMC concentration. The further ITC and docking simulations suggested the bindings of MEL-A toward β-glucosidase were driven by weak hydrophobic interactions happened between the amino acid residues of β-glucosidase and the fatty acid residues of MEL-A, in addition to hydrogen bonds between amino acids and hydroxyl in glycosyl residues of this biosurfactant.