Investigating the Antioxidant Capacity of Lunasin Expressed in Aspergillus oryzae

Abstract

Objective: Lunasin is a bioactive protein that possesses anti-carcinogenic, anti-inflammatory, and antioxidant properties. Traditional isolation methods are resource-intensive, and chemical synthesis faces cost and environmental issues. This study aims to achieve cost-effective lunasin expression in Aspergillus oryzae with a focus on exploring its antioxidant properties in vitro. Materials and Methods: The expression vector carrying four lunasin sequences fused with amylase and an 8xHis-tag was introduced into pyrG auxotrophic A. oryzae. Subsequently, the recombinant protein was purified using metal affinity chromatography. The study uses sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), western blot analyses, and size-exclusion chromatography to evaluate the composition and purity of the protein, a linoleic acid assay to demonstrate the inhibitory effect on lipid peroxidation, and the 2,2\"-azinobis-[3-ethylbenzothiazoline-6-sulfonic acid] ABTS) assay to evaluate the radical scavenging activity. Results: SDS-PAGE and western blot analyses confirmed sustained lunasin expression in A. oryzae, appearing in both fusion and non-fusion forms. Yields were 5.8 mg/L for non-fusion and 4 mg/L for fusion lunasin expression. Moreover, 0.1 μM non-fusion lunasin surpassed α-tocopherol and butylated hydroxyanisole (BHA; p < 0.05) in reducing lipid peroxidation at 4 and 72 h. Unlike the fusion lunasin, the non-fusion lunasin displayed concentration- and time-independent inhibitory effects on linoleic acid peroxidation as well as significant ABTS scavenging activity (p < 0.05). Conclusion: The study has shown for the first time A. oryzae to efficiently express and secrete both fusion and non-fusion lunasin proteins in a soluble form, with the non-fusion lunasin exhibiting superior antioxidant effectiveness compared to the fusion lunasin. The findings underscore A. oryzae\"s potential as a promising host for producing functional lunasin with antioxidant properties, opening avenues for broader applications in biotechnology and bioactive peptides.