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Unravelling biochemical and molecular mechanism of a carboxylesterase from Dietzia kunjamensis IITR165 reveal novel activities against polyethylene terephthalate
Plastics and plasticizers accumulate in the ecological niches affecting biodiversity, and human and environmental health. Bacteria degrading polyethylene terephthalate (PET) were screened and PETases involved in PET degradation were characterized. Here, we identified a carboxylesterase Dkca1 of 48.44 kDa molecular mass from Dietzia kunjamensis IITR165 shown to degrade amorphous PET film into bis(2-hydroxyethyl) terephthalate (BHET) and terephthalic acid (TPA) formed 64.35 μM and 35.26 μM, respectively within 96 h at 37 °C as revealed by LC-MS analysis showed significant PET hydrolase activity similar to reported PETases. SEM analysis confirms the surface erosion as cavities and holes. Dkca1 also hydrolysed BHET and dibutyl phthalate (DBP) at a concentration of 1 mM within 3 h indicating its versatility. Fluorescence quenching shows Dkca1 protein has a maximum affinity (Kd) towards BHET (86.55 μM) than DBP (134.2 μM). The protein demonstrated high stability under temperatures above 40 °C and at the pH range of 6.0-9.0. Moreover, Amino acid composition showed that the Dkca1 enzyme belongs to family VII carboxylesterase containing conserved catalytic triad of Ser183-Glu289-His378 with pentapeptide motif GXSAG and an oxyanion hole H103GGG106, sharing 37.47 % and 32.44 % similarity with a PET hydrolase TfCa from Thermobifida fusca and PAE hydrolase CarEW from Bacillus sp. K91, respectively. A docking study revealed that ligand PET, BHET, and DBP showed favourable binding in the catalytic pocket of the Dkca1 protein.
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