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

Abstract

The rate response of poly(ethylene terephthalate) (PET)-hydrolases to increased substrate crystallinity (XC) of PET manifests as a rate-lowering effect that varies significantly for different enzymes. Herein, we report the influence of XC 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 XC. The recently discovered PET-hydrolase PHL7 worked efficiently on “amorphous” PET disks (XC≈10 %), but this enzyme was extremely sensitive to increased XC, whereas the enzymes LCCICCG, LCC, and DuraPETase had higher tolerance to increases in XC and had activity on PET disks having XC of 24.4 %. Microscopy revealed that the XC-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.