Directed Evolution ofPseudomonas fluorescensLipase Variants With Improved Thermostability Using Error-Prone PCR

Lipases catalyze the hydrolysis of fats and oils, and have been widely used in various industrial fields. However, bacterial lipases have a lower thermostability in industrial processes, which was a limiting factor in their industrial application. In this study, we obtained an improve variant ofPseudomonas fluorescenslipase (PFL) with enhanced thermostability using classical error-prone PCR. Wild-type PFL showed an optimal temperature and pH of 50 degrees C and pH 7.5, respectively. Due to the low thermostability of PFL, a library containing over 3000 individual mutants as constructed using error-prone PCR. Screening for thermotolerance yielded the mutants L218P and P184C/M243C withT(m)values of 62.5 and 66.0 degrees C, which was 2.5 and 6 degrees C higher than that of the WT, respectively. The combination of the two mutants (P184C/M243C/L218P) resulted in an approximately additive effect with aT(m)value of 68.0 degrees C. Although the increase ofT(m)was not substantial, the mutant also had dramatically increased methanol tolerance. Structural analysis revealed that the introduction of a disulfide bond between P184C and M243C and the substitution of Pro to reduce the flexibility of a loop increased the thermostability of PFL, which provides a theoretical foundation for improving the thermostability and methanol tolerance of lipase family I.1 to resist the harsh conditions of industrial processes.