Improving the activity and thermostability of PETase from Ideonella sakaiensis through modulating its post-translational glycan modification.

The large-scale preparation of Polyehylene terephthalate (PET) hydrolysing enzymes in low-cost is critical for the biodegradation of PET in industry. In the present study, we demonstrate that the post-translational glycosylation of Pichia pastoris makes it a remarkable host for the heterologous expression of PETase from Ideonella sakaiensis 201-F6 (IsPETase). Taking advantage of the abundant N- and O-linked glycosylation sites in IsPETase and the efficient post-translational modification in endoplasmic reticulum, IsPETase is heavily glycosylated during secretory expression with P. pastoris, which improves the specific activity and thermostability of the enzyme dramatically. Moreover, the specific activity of IsPETase increased further after the bulky N-linked polysaccharide chains were eliminated by Endo-ß-N-acetylglucosaminidase H (Endo H). Importantly, the partially deglycosylated IsPETase still maintained high thermostability because of the remaining mono- and oligo-saccharide residues on the protein molecules. Consequently, the partially deglycosylated IsPETase was able to be applied at 50 °C and depolymerized raw, untreated PET flakes completely in 2 to 3 days. This platform was also applied for the preparation of a famous variant of IsPETase, Fast-PETase, and the same result was achieved. Partially deglycosylated Fast-PETase demonstrates elevated efficiency in degrading postconsumer-PET trays under 55 °C than 50 °C, the reported optimal temperature of Fast-PETase. The present study provides a strategy to modulate thermostable IsPETase through glycosylation engineering and paves the way for promoting PET biodegradation from laboratories to factories.

Degradation of CP4-EPSPS with a Psychrophilic Bacterium Stenotrophomonas maltophilia 780.

CP4-EPSPS (Agrobacterium sp. strain CP4 5-enolpyruvylshikimate-3-phosphate synthase) protein showed remarkable thermostability and was highly resistant to proteases, such as trypsin. In order to eliminate the pollution of CP4-EPSPS from the accumulated straws to the surrounding environment during the winter, the present study investigated the extracellular proteases of 21 psychrophilic strains isolated from the south polar region. The results indicated that Stenotrophomonas maltophilia 780 was able to degrade CP4-EPSPS at 18 °C efficiently. Further study indicated that it was able to grow in the extract of Roundup Ready soybean at 18 °C, with CP4-EPSPS degraded to an undetectable level within 72 h. The extracellular proteases of Stenotrophomonas maltophilia 780 are thermo-sensitive, with an optimal temperature of 65 °C. The genomic sequencing result indicated that this strain had more than a hundred putative protease and peptidase coding genes, which may explain its high capability in decomposing CP4-EPSPS.