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

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 <i>V</i>_max and <i>K</i>_m of β-glucosidase. The thermodynamics and structural data demonstrated that the midpoint temperature (<i>T</i>_m) and unfolding enthalpy (Δ<i><i>H</i></i>) 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

Structural Characterization and Anticancer Activity of Cell-Bound Exopolysaccharide from <i>Lactobacillus helveticus</i> MB2‑1

A novel cell-bound exopolysaccharide (c-EPS) was isolated from <i>Lactobacillus helveticus</i> MB2-1 by ultrasonic extraction, anion exchange, and gel filtration chromatography before being structurally characterized. The c-EPS is a heteropolysaccharide with an average molecular weight of 1.83 × 10⁵ Da and is composed of glucose, mannose, galactose, rhamnose, and arabinose at a molar ratio of 3.12:1.01:1.00:0.18:0.16. Methylation analysis and nuclear magnetic resonance analysis revealed that the c-EPS is a linear glucomannogalactan containing repeating units of →6)-β-d-Man<i>p</i>-(1 → 3)-β-d-Glc<i>p</i>-(1 → 3)-β-d-Glc<i>p</i>-(1 → 3)-β-d-Glc<i>p</i>-(1 → 4)-α-d-Gal<i>p</i>-(1→ and trace amounts of Rha<i>p</i>-(1→ and (1 → 4)-Ara<i>p</i> residues. Complex formation with Congo red demonstrated a triple-strand helical conformation for the c-EPS. Scanning electron microscopy of the c-EPS revealed many regular feather-like structural units. Topographical examination of c-EPS by atomic force microscopy revealed that the c-EPS formed rounded-to-spherical lumps with different sizes and chain formations. Furthermore, preliminary in vitro tests revealed that c-EPS significantly inhibited the proliferation of HepG-2, BGC-823, and especially HT-29 cancer cells