Bridging the Gap in the Structure-Function Paradigm of Enzymatic PET Degradation - Aromatic Residue Driven Balanced Interactions with Catalytic and Anchoring Subsite.

Understanding all parameters contributing to enzyme activity is crucial in enzyme catalysis. For enzymatic PET degradation, this involves examining the formation of the enzyme-PET complex. In IsPETase (WT), a PET-degrading enzyme from Ideonellasakaiensis, mutating two non-catalytic residues (DM) significantly enhances activity. Such mutations, depending on their position in the tertiary structure, fine-tune enzyme function. However, detailed molecular insights into these mutations' structurefunction relationship for PET degradation are lacking. This study characterizes IsPETase's catalytic ability compared to WT TfCut2 using molecular dynamics simulations and quantum mechanical methods. We explore the conformational landscape of the enzyme-PET complex and quantify residue-wise interaction energy. Notably, aromatic and hydrophobic residues Tyr, Trp, and Ile in the catalytic subsite S1, and aromatic Phe and polar Asn in the anchoring subsite S3, crucially optimize PET binding. These residues enhance PET specificity over non-aromatic plastics. Our findings suggest that the balance between binding at subsite S1 and subsite S3, which is influenced by cooperative mutations, underlies catalytic activity. This balance shows a positive correlation with experimentally obtained kcat/Km values: WT TfCut2 < WT IsPETase << DM IsPETase.