Rational design of alginate lyase ALYI1 for improving the antioxidant activity of the alginate oligosaccharides

To achieve the cost-effective alginate oligosaccharides production, we have developed a novel rational design strategy that optimized capture behavior, orientation movement and hydrogen bond interaction of substrate in alginate lyase ALYI1. This approach led to S56D and G258Q advantageous variants balancing the trade-off challenge, particularly S56D, which exhibited a 1.56-fold increase in specific activity and 23.11 % higher activity at 45 °C for 1 h compared to ALYI1. The variants exhibited reduced binding fluctuation and more favorable binding energy compared to ALYI1, which was ascribed to more favorable dynamic hydrogen bonds and binding energy distribution. Furthermore, we innovatively found that alginate oligosaccharides produced by S56D and G258Q displayed increasing ABTS⁺ and DPPH^• radical scavenging efficiencies than those produced by ALYI1. Especially, S56D degradation product demonstrated 10.80 % higher ABTS⁺ radical and 29.75 % higher DPPH^• radical scavenging activities at 1.0 mg/mL. This was attributed to the improved disaccharides and trisaccharides ratios in the product. Our findings provide critical insights and establish a robust foundation for the development of superior biocatalysts for the industrial production of AOS.