Biocatalytic Preparation of High-Purity DHA-Enriched Partial Glycerides through Semirational Design and Modification of Lipase Lip1897

High-purity docosahexaenoic acid (DHA) partial glycerides (PG) supplements have promising market prospects. In this study, a novel lipolytic enzyme family I lipase Lip1897, derived from Streptomyces thermodiastaticus, was identified and modified to be applied to the enzymatic synthesis of high-purity docosahexaenoic acid partial glycerides (DHA-PG). Lip1897 displayed optimal activity and good stability at 55 °C and pH 5.0. Further study found that Lip1897 could catalyze the hydrolysis of DHA triglycerides (TG) and DHA ethyl esters (EE), the esterification of DHA, and the glycerolysis of docosahexaenoic acid ethyl esters (DHA-EE), which had good prospects for industrial application. To enhance the catalytic selectivity of Lip1897, semirational design and modification based on structural analysis were carried out, and the mutant Lip1897-H106W showed a 1.86-fold increase in glycerolysis activity. The molecular docking results indicated that the mutant bound to the substrate DHA-EE at lower energy and with a more stable conformation. Under the solvent-free system, Lip1897-H106W was employed to catalyze the glycerolysis of DHA-EE for the synthesis of DHA-PG, achieving a promising DHA-EE conversion rate of 95.02% and a high DHA-PG yield of 70.85%. The efficient glycerolysis for preparing high-purity DHA-PG was realized. This research provides a reference for enhancing the efficiency of specific configurational functional lipid biosynthesis through enzyme discovery and modification.