Due to the steric effects imposed by bulky polymers, the formation of catalytically competent enzyme and substrate conformations is critical in the biodegradation of plastics. In poly­(ethylene terephthalate) (PET), the backbone adopts different conformations, gauche and trans, coexisting to different extents in amorphous and crystalline regions. However, which conformation is susceptible to biodegradation and the extent of enzyme and substrate conformational changes required for expedient catalysis remain poorly understood. To overcome this obstacle, we utilized molecular dynamics simulations, docking, and enzyme engineering in concert with high-resolution microscopy imaging and solid-state nuclear magnetic resonance (NMR) to demonstrate the importance of conformational selection in biocatalytic plastic hydrolysis. Our results demonstrate how single-amino acid substitutions in Ideonella sakaiensis PETase can alter its conformational landscape, significantly affecting the relative abundance of productive ground-state structures ready to bind discrete substrate conformers. We experimentally show how an enzyme binds to plastic and provide a model for key residues involved in the recognition of gauche and trans conformations supported by in silico simulations. We demonstrate how enzyme engineering can be used to create a trans-selective variant, resulting in higher activity when combined with an all-trans PET-derived oligomeric substrate, stemming from both increased accessibility and conformational preference. Our work cements the importance of matching enzyme and substrate conformations in plastic hydrolysis, and we show that also the noncanonical trans conformation in PET is conducive for degradation. Understanding the contribution of enzyme and substrate conformations to biocatalytic plastic degradation could facilitate the generation of designer enzymes with increased performance.

Angiotensin IV (Ang IV) and related peptide analogs, as well as nonpeptide inhibitors of insulin-regulated aminopeptidase (IRAP), have previously been shown to enhance memory and cognition in animal models. Furthermore, the endogenous IRAP substrates oxytocin and vasopressin are known to facilitate learning and memory. In this study, the two recently synthesized 13-membered macrocyclic competitive IRAP inhibitors HA08 and HA09, which were designed to mimic the N terminus of oxytocin and vasopressin, were assessed and compared based on their ability to bind to the IRAP active site, and alter dendritic spine density in rat hippocampal primary cultures. The binding modes of the IRAP inhibitors HA08, HA09, and of Ang IV in either the extended or g-turn conformation at the C terminus to human IRAP were predicted by docking and molecular dynamics simulations. The binding free energies calculated with the linear interaction energy method, which are in excellent agreement with experimental data and simulations, have been used to explain the differences in activities of the IRAP inhibitors, both of which are structurally very similar, but differ only with regard to one stereogenic center. In addition, we show that HA08, which is 100-fold more potent than the epimer HA09, can enhance dendritic spine number and alter morphology, a process associated with memory facilitation. Therefore, HA08, one of the most potent IRAP inhibitors known today, may serve as a suitable starting point for medicinal chemistry programs aided by MD simulations aimed at discovering more drug-like cognitive enhancers acting via augmenting synaptic plasticity.