Engineering of Candida antarctica lipase B for poly(ε-caprolactone) synthesis

Development of novel synthetic routes based on more eco-friendly processes, such as enzyme-based catalysis, are in great demand to produce biopolymers. Among them, enzymatic Ring Opening Polymerization (eROP) of lactones using lipases, such as Candida antarctica lipase B (CalB), offers new opportunities, although they have been mostly explored in wild-type form. In this study, we followed a structure-based engineering strategy to redesign CalB active site in order to improve catalytic efficiency of poly(e-caprolactone) synthesis and size of polymer products. A library of 1410 single mutants was constructed by saturation mutagenesis that targeted 15 amino acid positions of the active site, identified by molecular modelling. Novel High-Throughput Screening (HTS) assays based either on the ring-opening of the lactone or the detection of poly(e-caprolactone) production were developed and used to screen the library. This led to the identification of 8 improved mutants, among which mutant I285R showed nearly 3-fold increase in catalytic efficiency for the e-caprolactone opening, first step of the reaction, and 30% increased poly(e-caprolactone) molar mass compared to parental wild-type CalB enzyme in same reaction conditions.