The insertion of (LK) residues at the N-terminus of Staphylococcus xylosus lipase affects its catalytic properties and its enantioselectivity

Two residues (LK) were inserted at the N-terminus of Staphylococcus xylosus lipase (SXL). The S. xylosus lipase wild-type (WT) and its constructed mutant (LK-SXL) were expressed in Escherichia coli BL21 (DE3) and purified to homogeneity using Sephacryl S-200 gel filtration, anion exchange and cation exchange chromatography.A comparative study on the kinetics and interfacial properties of the SXL wild-type and its mutant was performed using emulsified and monolayer substrate. The first important observation was that the insertion of two residues (LK) resulted in an improvement in temperature activity, a better stability, a 3-fold specific activity and a 6-fold catalytic efficiency (kcat/Kmapp), compared to the SXL wild-type.Using the monolayer technique, this study showed that the inserted residues (LK) at the N-terminus do not affect the adsorption step of the S. xylosus lipase into a monomolecular film of diC12-phosphatidyl-choline.A kinetics study on the surface pressure dependency, stereoselectivity, and regioselectivity of the SXL wild-type and its mutant was also performed using the three dicaprin isomers spread as monomolecular films at the air-water interface. Furthermore, the insertion of two residues (LK) at the N-terminus of S. xylosus lipase was shown to be accompanied by the switch of its enantioselectivity.To confirm that the insertion of LK residues at the N-terminus of SXL affects both the hydrolysis properties and the synthesis, new experiments were performed and the production of butyl acetate by SXL before and after LK insertion was assessed. The insertion of these residues may have some valuable applications in industry.