Background: Fungal lipase dependent processes are important for their pathogenicity.
Lipases can therefore be explored as direct target of promising herbal antifungals.
Objective: We explored Aspergillus niger lipase as a direct target of eugenol through spectroscopic
techniques and compare results with Bovine Serum Albumin and lysozyme to comment on
selectivity of eugenol towards lipase.
Methods: In vitro activity assays of lipase are used to determine concentration ranges. UV-Visible,
Fluorescence and Circular dichroism spectroscopy were employed to determine binding constant,
stoichiometric binding sites and structural changes in Lipase, BSA and lysozyme following
incubation with varying concentrations of eugenol.
Results: In activity assays 50% inhibition of lipase was obtained at 0.913 mmoles/litre eugenol.
UV-vis spectroscopy shows formation of lipase-eugenol, Bovine Serum Albumin-eugenol and
lysozyme-eugenol complex well below this concentration of eugenol. Eugenol binding caused blue
shift with Bovine Serum Albumin and lysozyme suggestive of compaction, and red shift with
lipase. Negative ellipticity decreased with lipase but increased with Bovine Serum Albumineugenol
and lysozyme-eugenol complexes suggesting loss of helical structure for lipase and
compaction for Bovine Serum Albumin and lysozyme. Binding of eugenol to lipase was strong
(Ka= 4.7 x 106 M-1) as compared to Bovine Serum Albumin and lysozyme. The number of
stoichiometric eugenol binding sites on lipase was found to be 2 as compared to 1.37 (Bovine
Serum Albumin) and 0.32 (lysozyme). Docking results also suggest strong binding of eugenol with
lipase followed by Bovine Serum Albumin and lysozyme.
Conclusion: Eugenol is found to be effective inhibitor and disruptor of secondary and tertiary
structure of lipase, whereas its binding to Bovine Serum Albumin and lysozyme is found to be
weak and less disruptive of structures suggesting selectivity of eugenol towards lipase.