Structure of the plastic-degrading Ideonella sakaiensis MHETase bound to a substrate

Gottfried J Palm,Gert Weber,Dominique Böttcher,Manfred S Weiss,Henrik Müller,Emil A P Michels,Lukas Reisky,Miriam C Walczak,Leona Berndt,Uwe T Bornscheuer

doi:10.1038/s41467-019-09326-3

Abstract

The extreme durability of polyethylene terephthalate (PET) debris has rendered it a long-term environmental burden. At the same time, current recycling efforts still lack sustainability. Two recently discovered bacterial enzymes that specifically degrade PET represent a promising solution. First, Ideonella sakaiensis PETase, a structurally well-characterized consensus α/β-hydrolase fold enzyme, converts PET to mono-(2-hydroxyethyl) terephthalate (MHET). MHETase, the second key enzyme, hydrolyzes MHET to the PET educts terephthalate and ethylene glycol. Here, we report the crystal structures of active ligand-free MHETase and MHETase bound to a nonhydrolyzable MHET analog. MHETase, which is reminiscent of feruloyl esterases, possesses a classic α/β-hydrolase domain and a lid domain conferring substrate specificity. In the light of structure-based mapping of the active site, activity assays, mutagenesis studies and a first structure-guided alteration of substrate specificity towards bis-(2-hydroxyethyl) terephthalate (BHET) reported here, we anticipate MHETase to be a valuable resource to further advance enzymatic plastic degradation.

Highlights

The extreme durability of polyethylene terephthalate (PET) debris has rendered it a long-term environmental burden
The structure of MHETase was solved by an molecular replacement (MR) pipeline employing a recent feruloyl esterase structure (PDB entry 6G21; see Methods)
The overall domain architecture of the 65 kDa MHETase resembles that of feruloyl esterases, with a lid domain inserted between β-strand 7 and α-helix 15 of the α/β-hydrolase fold (Fig. 1b, Supplementary Fig. 1)

Summary

Introduction

The extreme durability of polyethylene terephthalate (PET) debris has rendered it a long-term environmental burden. Ideonella sakaiensis PETase, a structurally well-characterized consensus α/β-hydrolase fold enzyme, converts PET to mono-(2-hydroxyethyl) terephthalate (MHET). In the light of structure-based mapping of the active site, activity assays, mutagenesis studies and a first structure-guided alteration of substrate specificity towards bis-(2-hydroxyethyl) terephthalate (BHET) reported here, we anticipate MHETase to be a valuable resource to further advance enzymatic plastic degradation. MHETase was initially assigned to the tannase enzyme family, which belongs to Block X of the α/β-hydrolase fold enzymes classified in the ESTHER database[10,22] This family includes fungal and bacterial tannases and feruloyl esterases. MHETase, is likely to possess a scaffold unprecedented for plasticdegrading enzymes This may be exploited in order to improve catalysis and to expand substrate specificity and significantly advance enzymatic plastic polymer degradation. We anticipate our data to significantly advance the current understanding of enzymes degrading synthetic polyesters

Methods

Results

Conclusion