Cooperative Amidase Systems Control Product Selectivity During Enzymatic Nylon Depolymerization

Abstract

Recent advances in enzymatic polyester depolymerization have highlighted the potential of biocatalysis for sustainable plastic recycling. In contrast, efficient enzymatic strategies for polyamide (PA) degradation remain limited. Here, we investigate how complementary amidases influence product formation during the enzymatic treatment of bulk nylon-6 (PA6) and nylon-6,6 (PA66). Guided by previously established substrate preferences, enzyme combinations are designed to couple NylC-mediated oligomer cleavage with downstream conversion by NylB or cyclic oligomer ring-opening by NylA. Sequential enzyme treatments demonstrate efficient conversion of characteristic PA6- and PA66-derived intermediates, while one-pot systems enable coordinated downstream conversion at 34°C–40°C. For PA6, NylB efficiently converts the NylC-generated 6-aminohexanoic acid dimer to 6-aminohexanoic acid, whereas for PA66, NylA selectively redirects accessible cyclic PA66-derived species toward the corresponding linear repeat-unit product. These changes in product distribution are not accompanied by a substantial increase in the overall amount of soluble polymer-derived material. The detected soluble products represent less than 1% of the initial polymer mass under the investigated conditions, demonstrating that overall soluble product release remains limited. Together, these results show that complementary amidases can control downstream intermediate conversion and product selectivity during enzymatic nylon depolymerization.