PETases

PETases are enzymes that catalyze the hydrolysis of polyethylene terephthalate (PET), a widely used plastic in bottles and fibers, converting it into smaller, more biodegradable compounds. They are part of the broader family of plastic-degrading enzymes and have attracted interest for potential biological recycling of PET waste. The most studied PETases come from the bacterium Ideonella sakaiensis, which can utilize PET as a carbon source.

Discovery and natural system: In 2016, Ideonella sakaiensis was isolated from an environment containing PET waste, and its enzyme IsPETase was identified as capable of breaking down PET at ambient temperatures. IsPETase works together with MHETase, another enzyme from the same organism, which further degrades the intermediate MHET into terephthalic acid and ethylene glycol, completing the depolymerization pathway.

Mechanism and structure: IsPETase is a serine hydrolase that adopts an alpha/beta hydrolase fold. It uses a catalytic triad consisting of serine, histidine, and aspartate to cleave the ester bonds in PET. The enzyme features a substrate-binding pocket that accommodates PET chains, and its activity is influenced by polymer crystallinity, temperature, and other environmental conditions.

Engineering and variants: Researchers have engineered PETase variants to improve thermostability and catalytic efficiency, including changes aimed at enhancing activity at moderate temperatures and against more crystalline PET. These engineered forms are studied to advance practical, scalable PET recycling and to broaden substrate scope.

Applications and challenges: PETases hold promise for biological recycling, waste remediation, and integration with chemical recycling streams. Challenges include limited activity on highly crystalline PET at ambient conditions, relatively slow depolymerization rates, need for pretreatment, and considerations of cost and industrial scalability.