Poly(butylene succinate-co-furandicarboxylate) (PBSF) and poly(butylene adipate-co-furandicarboxylate) (PBAF) are novel furandicarboxylic acid-based biodegradable copolyesters with great potential to replace fossil-derived terephthalic acid-based plastics such as poly(butylene adipate-co-terephthalate) (PBAT) and polyethylene terephthalate (PET). In this study, a combination of molecular docking, molecular dynamics simulation, quantum chemistry techniques, wave function analysis, and site-directed mutations were employed to investigate the degradation mechanism of PBSF and PBAF catalyzed by Candida antarctica lipase B (CALB). Computational analysis indicates that the catalytic reaction follows a four-step mechanism resembling the ping-pong bibi mechanism, with the initial two steps being acylation reactions and the subsequent two being hydrolysis reactions. Notably, the first step of the hydrolysis is identified as the rate-determining step. Moreover, by introducing single-point mutations to expand the substrate entrance tunnel, the catalytic distance of the first acylation step decreased. Additionally, energy barrier of the rate-determining step is decreased in the PBSF system by site-directed mutations on increasing hydrophobicity of the enzyme active site. This study unprecedently showed a comprehensive understanding of the molecular mechanism of copolyesters degradation and a novel approach for semi-rational design of the CALB enzyme, which is the substrate binding pocket and hydrophobicity of the enzyme active site have the potential to be engineered to enhance the degradation of copolyesters.
 

可降解塑料,多尺度理论计算,酶催化