Poly(L-lactide)-Degrading Enzyme from Laceyella sacchari LP175: Cloning, Sequencing, Expression, Characterization and Its Hydrolysis of Poly(L-lactide) Polymer

Abstract

In this study, the poly-(L-lactide) (PLLA)-degrading enzyme from the thermophilic filamentous bacterium, Laceyella sacchari LP175 was characterized for application in biological recycling process. The gene encoding the PLLA-degrading gene (plla_lp175) was cloned and expressed in Escherichia coli. The native protein comprises 383 amino acids with a molecular mass and pI of 39.45 kDa and 8.26, respectively. The recombinant protein was purified by one-step purification, and was found to have a molecular weight of 28 kDa. Functional expression of PLLA_LP175 in E. coli with a pMAL-c5X vector enhanced the expression of PLLA-degrading enzyme up to 756 U/mg of protein, which is a 2.3-fold increase compared to the native strain. The purified recombinant protein is active in the range of pH 7.0–9.0 and 45- 60 °C, with optimum activity at pH 9.0 and 60 °C. The recombinant enzyme could hydrolyse PLLA objects to a different extent depending on PLLA composition, at pH 9.0 and 50 °C within 24 h. Monomeric lactic acid was detected as the product from enzymatic degradation of PLLA objects. A scanning electron micrograph, showing a rough surface with holes of all PLLA objects after treatments with the recombinant enzyme, confirmed the ability of this enzyme to degrade PLLA objects.