Gene structure and comparative study of two different plastic-degrading esterases from Roseateles depolymerans strain TB-87

The structures of two genes from Roseateles depolymerans strain TB-87 encoding the esterases Est-H and Est-L, which can degrade aliphatic-aromatic copolyesters, were annotated. Two open reading frames (ORFs) consisting of 1083 bp and 870 bp nucleotides, corresponding to est-H and est-L, encoding enzymes of 290 and 289 amino acids, respectively, were predicted. In addition, another ORF consisting of 735 bp encoding a chaperone-like protein (Est-Ch) of 244 amino acids was identified in the intergenic region of est-H and est-L. The presence of a promoter region upstream of est-H and the absence of a terminator region downstream of the ORF and vice versa for est-Ch, suggests that est-H and est-Ch are polycistronically expressed. A homology search for Est-H and Est-L revealed homology with plastic degrading enzymes, such as esterases and cutinases, while Est-Ch showed homology with a bacterial lipase chaperone. As consensus lipase sequences (-Gly-His-Ser-Met-Gly-) were observed in these enzymes, Est-H and Est-L were hypothesized to be hydrolases with serine (Ser) in their active center. Three-dimensional structures of Est-H and Est-L without their putative signal sequences were constructed using Est119 from Thermobifida alba strain AHK119 as the template; the structures and positions of the catalytic triad (Ser, Asp, His) active centers were similar to those of Est119. A mutant strain in which the annotated esterase-encoding genes were disrupted using a homologous recombination method lost the ability to form a clear zone on poly(butylene succinate-co-adipate (PBSA) emulsion-overlaid nutrient agar plates. Characterization of the esterases from strain TB-87 could contribute to the development of novel biodegradable plastics with unique properties such as recyclable monomers.