Molecular understanding of enzyme stabilization toward functional enzymatic materials

Enzymes are powerful natural catalysts that have long been promising as building blocks for functional materials. However, enzymes are only marginally stable in their natural environments—moderate temperature and aqueous solvents—so any perturbations to these ideal conditions tend to denature and/or deactivate enzymes. This instability in nonnatural environments has severely hindered the technological relevance of enzymes./nHere, I used amphiphilic random heteropolymers (RHPs) as a platform to understand and mediate enzyme stability in various nonnatural environments. RHPs are designed so that their compositions and sequences facilitate noncovalent interactions that are strong enough to stabilize the native state of enzymes while remaining soft enough so as to not outcompete the primary forces that govern enzyme folding. While RHPs were initially designed to stabilize enzymes in organic solvents, their versatility is such that they can modulate enzymes’ stability, activity, and reaction mechanisms in a variety of situations./nRHPs can stabilize enzymes over long time periods in organic solvents, enabling versatile material fabrication techniques via electrospinning, film casting, spin coating, and 3-D printing. The ensuing enzyme-based functional materials can serve as reusable catalysts with exceptional stability due to confinement in a polymeric matrix./nRHPs can mediate the local microenvironment of enzymes in water as they adsorb to hydrophobic interfaces. Enzymes like organophosphorus hydrolase (OPH) and chymotrypsin become unstable as their hydrophobic substrates phase separate at high concentrations, likely because the enzymes’ binding site loops are susceptible to local conformational changes at hydrophobic interfaces. RHPs provide sufficient short-range interactions to stabilize the native state conformation of these enzymes, facilitating efficient two-phase catalysis in water./nRHPs can drive adsorption of enzymes from the organic phase to an oil/water interface, where the enzymatic behavior changes significantly from that in the bulk solvent. RHPs form nanoscopic clusters with enzymes in organic solvents, and the amphiphilicity of RHPs makes these clusters particularly surface active. The low dielectric of nonpolar organic solvents can be exploited to maintain enzyme latency in the pure organic solvent and trigger activation as conformational changes occur during adsorption to the oil/water interface./nFinally, RHPs can modulate the behavior of embedded enzymes when the confining polymer matrix is also a macromolecular substrate of the enzyme. This behavior enables fabrication of bioactive plastics with on-demand degradation in water. The embedded enzyme’s active site determines the degradation pathway and rate, while the matrix’s hierarchical and single chain structure offer thermodynamic and kinetic control over degradation. The RHP not only interacts with the embedded enzymes but can also interact with the polymer matrix, causing degradation recalcitrance that can be overcome by exploiting synergistic enzyme mechanisms./nThe results discussed in this dissertation offer new scientific insights into enzyme stability and may lead to functional materials with immediate technological relevance.

Advisor: Xu, Ting