Polyethylene terephthalate (PET) pollution is an emerging environmental hazard because of its recalcitrance to degradation. This study proposes an in silico mutagenesis of LipKV1 from Acinetobacter haemolyticus for improved lipase-PET interaction, using the PET-degrading Thermobifida cutinase (TfCut2) as the structural benchmark. Results revealed that lid deletion on LipKV1 (LipKV1_LE) facilitated the entry of PET into the active site. The mutation of several predicted amino acids into alanine expanded the LipKV1 active site for better PET binding. Docking results indicated that the LipKV1_LE mutants, Var9 (-6.2 kcal/mol), Var18 (-6.0 kcal/mol), and Var181 (-6.0 kcal/mol), produced higher binding affinities with PET than the wild-type LipKV1 (-2.5 kcal/mol) and TfCut2 (-4.6 kcal/mol), attesting that the selected mutation sites played prominent role in altering the abilities of LipKV1_LE mutants to bind to PET. Our molecular dynamics (MD) simulation results corroborated the variant-PET complexes' improved binding, mirrored by their improved conformations (RMSD ∼0.35 nm). The RMSF results also showed acceptable fluctuation limits of the LipKV1_PET mutant complexes (RMSF < 0.5 nm). Rg data of the complexes showed that they are conformationally stable, with a maximum of three H-bonds in their interaction with PET. SASA results showed that the mutations did not profoundly alter the hydrophobicity of the amino acid residues. MM-PBSA calculations on the LipKV1_PET mutant complexes estimated binding free energies between -28.29 kcal/mol to -23.25 kcal/mol, comparable to the molecular docking data. Thus, the MD data conveyed the practicality of the above-said site mutations in rationally designing the LipKV1 active site for better PET degradation.
Plastic or microplastic pollution is a global threat affecting ecosystems, with the current generation reaching as much as 400 metric tons per/year. Soil ecosystems comprising agricultural lands act as microplastics sinks, though the impact could be unexpectedly more far-reaching. This is troubling as most plastic forms, such as polyethylene terephthalate (PET), formed from polymerized terephthalic acid (TPA) and ethylene glycol (EG) monomers, are non-biodegradable environmental pollutants. The current approach to use mechanical, thermal, and chemical-based treatments to reduce PET waste remains cost-prohibitive and could potentially produce toxic secondary pollutants. Thus, better remediation methods must be developed to deal with plastic pollutants in marine and terrestrial environments. Enzymatic treatments could be a plausible avenue to overcome plastic pollutants, given the near-ambient conditions under which enzymes function without the need for chemicals. The discovery of several PET hydrolases, along with further modification of the enzymes, has considerably aided efforts to improve their ability to degrade the ester bond of PET. Hence, this review emphasizes PET-degrading microbial hydrolases and their contribution to alleviating environmental microplastics. Information on the molecular and degradation mechanisms of PET is also highlighted in this review, which might be useful in the future rational engineering of PET-hydrolyzing enzymes.