Rate Response of Poly(Ethylene Terephthalate)‐Hydrolases to Substrate Crystallinity: Basis for Understanding the Lag Phase

Crystal clear: We evaluate the significance of poly(ethylene terephthalate) (PET) crystallinity on enzymatic degradation rates of six PET hydrolysing enzymes, present a new quantitative assessment of PET crystallinity tolerance of the enzymes, and provide structural comparisons and molecular dynamics simulations of the enzymes to explain their differences in attack mode, lag phase, and enzymatic rate responses to increased PET substrate crystallinity.

Abstract

The rate response of poly(ethylene terephthalate) (PET)-hydrolases to increased substrate crystallinity (X _C) of PET manifests as a rate-lowering effect that varies significantly for different enzymes. Herein, we report the influence of X _C on the product release rate of six thermostable PET-hydrolases. All enzyme reactions displayed a distinctive lag phase until measurable product formation occurred. The duration of the lag phase increased with X _C. The recently discovered PET-hydrolase PHL7 worked efficiently on “amorphous” PET disks (X _C≈10 %), but this enzyme was extremely sensitive to increased X _C, whereas the enzymes LCC_ICCG, LCC, and DuraPETase had higher tolerance to increases in X _C and had activity on PET disks having X _C of 24.4 %. Microscopy revealed that the X _C-tolerant hydrolases generated smooth and more uniform substrate surface erosion than PHL7 during reaction. Structural and molecular dynamics analysis of the PET-hydrolyzing enzymes disclosed that surface electrostatics and enzyme flexibility may account for the observed differences.

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