Description
Wide spreading and utilization of plastic polyethylene terephthalate (PET) in the world has caused a large quantity of environmental challenges and gained much attention. Because of its nonbiodegradability, a large amount of plastic waste accumulation forms a global environmental crisis [1]. Notably, in 2016, Yoshida et al. reported the discovery of the bacterium, Ideonella sakaiensis [2]. Microbe Ideonella sakaiensis was reported to be capable of secreting two efficient enzymes to deconstruct PET polymers in mild temperature. First, Ideonella sakaiensis PETase, a structurally well-characterized consensus α/β-hydrolase fold enzyme, converts PET to mono-(2-hydroxyethyl) terephthalate (MHET). MHETase, the second key enzyme, hydrolyzes MHET to the PET educts terephthalate and ethylene glycol [3].
However, this two-enzyme system degradation capacity is highly limited by inhibition effects, diffusion of intermediates and PET surface physicochemical properties [4]. Here, we design a delicate multicomplex enzyme system, in which short peptide tags (RIAD and RIDD) are applied to create scaffold-free modular enzymes assemblies [5]. In order to effectively degrade microplastic PET particles, we construct enzymes of IsPETase and MHETase and protein hydrophobin in our complex system via scaffold modular part, which reveal higher catalytic efficiency in mild temperature. All proteins involved have unique functions in our system. IsPETase and MHETase are two enzymes involved deconstructing polymer PET plastic to MHET and MHET to TPA molecules, respectively. And hydrophobin protein, a small fungal protein, possess positive effects on altering the physicochemical properties of PET surfaces and enzyme aggregation enhancement when it was fused with PET degradation enzyme cutinase [6]. In conclusion, our work presents an innovative strategy to improve PET degradation via biosynthetic factories and artificially designed proteins system that do not exist in the nature.