Abstract
Plastics, such as the polyethylene terephthalate (PET), are widely used for various industrial applications, due to their physicochemical properties which are particularly useful in the packaging industry. However, due to improper plastic waste management and difficulties in recycling, post-consumer plastic waste has become a pressing issue for both the environment and for human health. Hence, novel technologies and methods of processing plastic waste are required to address these issues. Enzymatic-assisted hydrolysis of synthetic polymers has been proposed as a potentially more efficient and environment-friendly alternative to the currently employed methods. Recently, a number of PET hydrolases have been described, and in particular a PETase derived from Ideonella sakaiensis 201-F6 (IsPETase), which appears to be the most efficient and substrate-specific bacterial PET hydrolase enzyme discovered to date. In order to further investigate this class of PETase-like enzymes, we employed an in silico-based screening approach on the biotechnologically relevant genus Streptomyces, including terrestrial and marine isolates; in a search for potential PETase homologs. From a total of 52 genomes analyzed, we were able to identify three potential PETase-like enzymes, all of which were derived from marine-sponge associated Streptomyces isolates. A candidate PETase-like gene (SM14est) was identified in Streptomyces sp. SM14. Further in silico characterization of the SM14est protein sequence and its predicted three-dimensional structure were performed and compared to the well-characterized IsPETase. Both the serine hydrolase motif Gly-x1-Ser-x2-Gly and the catalytic triad Ser, Asp, His are conserved in both sequences. Molecular docking experiments indicated that the SM14est enzyme possessed the capacity to bind plastics as substrates. Finally, polyesterase activity was confirmed using a polycaprolactone (PCL) plate clearing assay which is a model substrate for the degradation of plastics; following heterologous expression of SM14est in Escherichia coli, with secretion being facilitated by the native Streptomyces signal peptide. These findings provide further insights into this important class of PETase-like enzymes.
Highlights
Plastics are materials that have been produced on a large scale from the 1950s onwards, and since have been widely used for various applications, and have become almost indispensable in modern society (Jambeck et al, 2015; Geyer et al, 2017; Lebreton and Andrady, 2019)
SM14 and enzyme activity was confirmed following heterologous expression of this gene in Escherichia coli. This is the first report of a PETase-like enzyme being identified in a marine sponge-derived Streptomyces spp. isolate, and we believe that this study provides further insights into our current knowledge of this important class of enzymes
A total of 15 of the most prominent PETase-like enzymes were selected to build the reference data set (Table 1), which was used to search for potential homologous proteins in the Streptomyces genomes data set
Summary
Plastics are materials that have been produced on a large scale from the 1950s onwards, and since have been widely used for various applications, and have become almost indispensable in modern society (Jambeck et al, 2015; Geyer et al, 2017; Lebreton and Andrady, 2019). In the 1960s, plastics accounted for less than 1% of municipal solid waste in the United States, but steadily increased to around 10% by 2005 in countries with middle to high income (Jambeck et al, 2015; Geyer et al, 2017) This was largely due to their advantageous properties, such as their low production cost and bio-inertia, which are useful for the packaging industry, when compared to other materials. SM14 and enzyme activity was confirmed following heterologous expression of this gene in Escherichia coli This is the first report of a PETase-like enzyme being identified in a marine sponge-derived Streptomyces spp. isolate, and we believe that this study provides further insights into our current knowledge of this important class of enzymes
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