Elucidating the binding efficacy of β‐galactosidase on polyaniline–chitosan nanocomposite and polyaniline–chitosan–silver nanocomposite: activity and molecular docking insights

Abstract

AbstractBACKGROUNDAspergillus oryzae β‐galactosidase (β‐gal; EC 3.2.1.23) was physically adsorbed on polyaniline–chitosan nanocomposite (PANI‐CS‐NC) and polyaniline–chitosan–silver nanocomposite (PANI‐CS‐Ag‐NC). Stability and kinetic studies were assessed, along with reusability and molecular docking interactions.RESULTSAccording to transmission electron microscopy images, the sizes of the respective NCs were found to be in the range of 23–39 and 6–18 nm. The η (effectiveness factor) values for PANI‐CS‐NC‐ and PANI‐CS‐Ag‐NC‐bound β‐gal were calculated to be 0.89 and 1.23, respectively, suggesting an enhancement in the activity of the enzyme in the presence of silver ions. Significant broadening was observed in pH and temperature profiles. Kinetic properties of PANI‐CS‐NC‐ and PANI‐CS‐Ag‐NC‐bound β‐gal showed lower Km, and two‐ and fourfold higher Vmax, respectively, compared to free enzyme. PANI‐CS‐Ag‐NC‐bound β‐gal was able to retain 94% of its initial activity after 10 repeated uses. Circular dichroism analysis revealed conformational changes in the secondary structure of protein upon immobilization. The genotoxic assessment revealed non‐toxic behaviour of both free and enzyme‐bound NC. The rate of lactose hydrolysis at 50 °C exhibited by PANI‐CS‐‐Ag‐NC bound β‐gal was 7% higher than that for the native enzyme. In‐silico analysis showed efficient binding of β‐gal on PANI‐CS‐ NCs due to interaction with residues that were exclusive of the active site of the enzyme.CONCLUSIONPANI‐CS‐Ag‐NC‐bound β‐gal preparation proved to be a robust nano‐biocatalyst due to remarkable enhancement in catalytic activity along with excellent stability and reusability characteristics, which could be further utilized for efficient construction of nano‐biosensors for producing lactose‐free dairy products to feed lactose‐intolerant patients. © 2018 Society of Chemical Industry