Ahmad_2019_Polym.Degrad.Stab_164_109

The structures of two genes fromRoseateles depolymeransstrain TB-87 encoding the esterases Est-H andEst-L, which can degrade aliphatic-aromatic copolyesters, were annotated. Two open reading frames(ORFs) consisting of 1083 bp and 870 bp nucleotides, corresponding toest-Handest-L, encoding enzymesof 290 and 289 amino acids, respectively, were predicted. In addition, another ORF consisting of 735 bpencoding a chaperone-like protein (Est-Ch) of 244 amino acids was identified in the intergenic region ofest-Handest-L. The presence of a promoter region upstream ofest-Hand the absence of a terminatorregion downstream of the ORF and vice versa forest-Ch, suggests thatest-Handest-Chare poly-cistronically expressed. A homology search for Est-H and Est-L revealed homology with plastic degradingenzymes, such as esterases and cutinases, while Est-Ch showed homology with a bacterial lipasechaperone. 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 constructedusing Est119 fromThermobifida albastrain AHK119 as the template; the structures and positions of thecatalytic triad (Ser, Asp, His) active centers were similar to those of Est119. A mutant strain in which theannotated esterase-encoding genes were disrupted using a homologous recombination method lost theability to form a clear zone on poly(butylene succinate-co-adipate (PBSA) emulsion-overlaid nutrientagar plates. Characterization of the esterases from strain TB-87 could contribute to the development ofnovel biodegradable plastics with unique properties such as recyclable monomers