The structural and molecular mechanisms of type II PETases: a mini review

The advent of plastics has led to significant advances for humans, although the accompanying pollution has also been a source of concern for countries globally. Consequently, a biological method to effectively degrade polyethylene terephthalate (PET) has been an area of significant scientific interest. Following the report of the highly efficient PET hydrolase from the bacterium Ideonella sakaiensis strain 201-F6 (i.e., IsPETase) in 2016, its structure has been extensively studied, showing that it belongs to the type II PETase group. Unlike type I PETases that include most known cutinases, structural investigations of type II PETases have only been conducted since 2017. Type II PETases are further divided into type IIa and IIb enzymes. Moreover, even less research has been conducted on type IIa plastic-degrading enzymes. Here, we present a review of recent studies of the structure and mechanism of type II PETases, using the known structure of the type IIa PETase PE-H from the marine bacterium Pseudomonas aestusnigri in addition to the type IIb enzyme IsPETase as representatives. These studies have provided new insights into the structural features of type II PETases that exhibit PET catalytic activity. In addition, recent studies investigating the rational design of IsPETases are reviewed and summarized alongside a discussion of controversies surrounding PETase investigations.