Identification and expression of MarCE, a marine carboxylesterase with synthetic ester‐degrading activity

Carboxylic ester hydrolases with the capacity to degrade polyesters are currently highly sought after for their potential use in the biological degradation of PET and other chemically synthesized polymers. Here, we describe MarCE, a carboxylesterase family protein identified via genome mining of a Maribacter sp. isolate from the marine sponge Stelligera stuposa. Based on phylogenetic analysis, MarCE and its closest relatives belong to marine‐associated genera from the Cytophaga–Flavobacterium–Bacteroides taxonomic group and appear evolutionarily distinct to any homologous carboxylesterases that have been studied to date in terms of structure or function. Molecular docking revealed putative binding of BHET, a short‐chain PET derivative, onto the predicted MarCE three‐dimensional structure. The synthetic ester‐degrading activity of MarCE was subsequently confirmed by MarCE‐mediated hydrolysis of 2 mM BHET substrate, indicated by the release of its breakdown products MHET and TPA, which were measured, respectively, as 1.28 and 0.12 mM following 2‐h incubation at 30°C. The findings of this study provide further insight into marine carboxylic ester hydrolases, which have the potential to display unique functional plasticity resulting from their adaptation to complex and fluctuating marine environmentsw. Here, we present MarCE, a marine carboxylesterase from a sea sponge‐derived Maribacter sp. isolate J2146c, identified by enzyme activity screening and subsequent genome mining of the J2146c strain. Computational protein analyses indicated the potential novelty of MarCE, which was phylogenetically linked to carboxylesterase family proteins from bacteria that have been exclusively associated with marine environments, and found to share low homology with previously characterized reference carboxylesterases. The terephthalate ester BHET was predicted to bind at the MarCE active site, and the enzyme was cloned and expressed in Escherichia coli enabling the confirmation of its BHET‐hydrolysing activity. The identification of MarCE contributes to the diversification of the current pool of enzymes that could be employed as biocatalysts in the degradation and transformation of synthetic substrates, particularly those associated with plastic waste.