Efficient depolymerization of polyethylene terephthalate (PET) and polyethylene furanoate by engineered PET hydrolase Cut190

Abstract

The enzymatic recycling of polyethylene terephthalate (PET) can be a promising approach to tackle the problem of plastic waste. The thermostability and activity of PET-hydrolyzing enzymes are still insufficient for practical application. Pretreatment of PET waste is needed for bio-recycling. Here, we analyzed the degradation of PET films, packages, and bottles using the newly engineered cutinase Cut190. Using gel permeation chromatography and high-performance liquid chromatography, the degradation of PET films by the Cut190 variant was shown to proceed via a repeating two-step hydrolysis process; initial endo-type scission of a surface polymer chain, followed by exo-type hydrolysis to produce mono/bis(2-hydroxyethyl) terephthalate and terephthalate from the ends of fragmented polymer molecules. Amorphous PET powders were degraded more than twofold higher than amorphous PET film with the same weight. Moreover, homogenization of post-consumer PET products, such as packages and bottles, increased their degradability, indicating the importance of surface area for the enzymatic hydrolysis of PET. In addition, it was required to maintain an alkaline pH to enable continuous enzymatic hydrolysis, by increasing the buffer concentration (HEPES, pH 9.0) depending on the level of the acidic products formed. The cationic surfactant dodecyltrimethylammonium chloride promoted PET degradation via adsorption on the PET surface and binding to the anionic surface of the Cut190 variant. The Cut190 variant also hydrolyzed polyethylene furanoate. Using the best performing Cut190 variant (L136F/Q138A/S226P/R228S/D250C-E296C/Q123H/N202H/K305del/L306del/N307del) and amorphous PET powders, more than 90 mM degradation products were obtained in 3 days and approximately 80 mM in 1 day. Graphical Abstract

Depolymerization of Polyester Fibers with Dimethyl Carbonate-Aided Methanolysis

“…GPC of the recovered textiles displayed a similar profile as that of the starting material (Figure S1), indicating that PET polymer chains were depolymerized and fragmented on the liquid−solid interface. 25 DSC analysis of the recovered textiles also showed a pattern similar to that of the starting material with a peak at 253 °C (Figure S2). The crystallinity of the recovered textiles was almost the same as that of the starting material (recovered textiles: 39%, starting material: 40%).…”

“…To date, an enzymatic approach − that enables depolymerization of amorphous PET into terephthalic acid at ambient temperature (∼50 °C) (Scheme b) has been reported, but it exhibits low activity toward polyester fibers . Molecular catalyst approaches under mild conditions − have also targeted amorphous PET resin, yet studies on polyester fibers are unexplored.…”

You get what you screen for: a benchmark analysis of leaf branch compost cutinase variants for polyethylene terephthalate (PET) degradation

“…64 The introduction of hydrophobic binding domains fused to the enzyme or the addition of ionic surfactants has also been successful in improving the interaction between polymer-degrading enzymes and the substrate. 52,65 As with DuraPETase, the substitution of glycine for alanine at position 170 in this work could also lead to a structural stabilisation of the helix, which is located directly adjacent to the serine of the catalytic triad. This reduction in Reaction Chemistry & Engineering Paper entropy in the coil region would therefore also stabilise the catalytic triad in general.…”

“…Even for the amorphous films, which are easier to degrade anyway, comminuted powders have been shown to degrade more than twice as well as the corresponding films. 52 Still, crystallinity has been found to play a much larger role than surface area for comminuted materials. 52,53 However, when comparing different substrates, it is useful to additionally relate the degradation to the specific surface area, i.e.…”

“…52 Still, crystallinity has been found to play a much larger role than surface area for comminuted materials. 52,53 However, when comparing different substrates, it is useful to additionally relate the degradation to the specific surface area, i.e. to specify the degradation rate per m 2 g PET −1…”