The role of binding modules in enzymatic poly(ethylene terephthalate) hydrolysis at high solids loadings

In nature, enzymes that deconstruct biological polymers, such as cellulose and chitin, often exhibit multi-domain architectures, comprising a catalytic domain and a non-catalytic binding module, the latter serves to increase the enzyme concentration at the substrate surface. This multi-domain architecture has been shown to improve the hydrolysis of poly(ethylene terephthalate) (PET) using engineered cutinase enzymes. Here, we examine the role of accessory binding modules at industrially-relevant PET solids loadings that will be necessary for cost-effective enzymatic recycling. Using a thermostable variant of the leaf compost cutinase (LCC), we produced synthetic fusion constructs of LCC with five Type A carbohydrate-binding modules (CBMs). At solids loadings below 10 wt%, the CBMs improve aromatic monomer yield from PET, but above this threshold, conversion extents up to 97% are reached with no added benefits from the presence of CBM fusions. This suggests that fusion constructs with the herein studied non-catalytic binding modules are not necessary for industrial enzymatic PET recycling.