Major challenges in searches for plastics-active enzymes
One of the major challenges will be the identification of novel enzymes for polymers for which none are currently known 11,52. Thus, we urgently need enzymes acting on PE, PP, PVC, but also on polymeric PA and PU ether bonds. Further we realized the lack of a common PET or PUR model substrate, which would allow the direct comparison of the kinetic parameters of different plastics-active enzymes. In contrast, kinetic analysis is generally performed for typical esterase substrates such as pNP-caproate. This data, however, does not allow a reliable prediction of the actual plastics activity. The few enzymes that have been characterized using polymers were tested on different polymer types, and pre-treatment was used to enable better degradation (see Table 1 for references). In addition, all kinetic data was recorded using single point measurements, thus the hydrolysis of the polymer could not be separated from the attachment of the enzyme to the polymer surface or from the hydrolysis of the resulting oligomers. Within this framework, a characterization of surface area and a control of surface properties such as crystallinity would be favourable to obtain better and more reliable kinetic data on the actual polymer.
The accumulation of verified plastics-active enzymes in databases with a reliable structure-function analysis will allow more predictive searches to rapidly and reliably identify novel and more active enzymes. Thereby it will allow to foster the search and development of novel pathways to create designer bugs using to solve the plastics problem.