Structural insights into an engineered feruloyl esterase with improved MHET degrading properties

Mono(2-hydroxyethyl) terephthalate (MHET) esterases (MHETases) are enzymes implicated in polyethylene terephthalate (PET) biodegradation. The present study elucidates the structural determinants that result in increased MHET degradation by a feruloyl esterase, which has been engineered to resemble the MHETase active site. The crystal structures of the variant in apo- and benzoic acid bound states reveal the changes induced by the introduced mutation, specifically the formation of a hydrogen bond and a trans to cis isomerization of a peptide bond in the vicinity of the catalytic site. Molecular dynamics simulations demonstrate the stabilization of the loop harboring the engineered residue, as well as an expansion of the substrate binding cleft, which would facilitate accommodation of a broader variety of substrates, indicative of a promiscuous biocatalyst.