Biocatalytic Nanomaterials: Mechanism of Enzyme Binding to Zirconium (IV) Phosphate Nano-Discs

Abstract

The ultimate goal of our studies is the understanding of the factors that control enzyme-solid interactions at the molecular level. It is crucial for the design of new solid supports to maximize bound enzyme functions. Enzymes bound to solids are widely used in a number of applications such as biosensors, protein arrays, biomedical implants, and biocatalysis. Yet, the details of enzyme binding to solids and the roles of these interactions on the bound enzyme behavior are poorly understood.

Here, we systematically examined the role of specific cations, the net charge of the enzyme and chemically-appended polymers on bound enzyme behavior. The central hypothesis is that enzyme binding to solids involves the binding or release of ions, water, protons and other spectator species present in the solutions, during the binding event. Free energy considerations indicate that stabilization of the native state and destabilization of the denatured state by interactions with the solid surface will enhance the thermodynamic stability of the bound enzyme. Thus, controlling the enzyme-solid interactions is essential to control bound enzyme behavior and this would require a detailed understanding of these interactions.

Our specific aims are: (1) to test if highly charged metal cations enhance the binding affinities of anionic enzymes to anionic solids while preserving the bound enzyme structure and activity, (2) to determine if controlled, chemical modification of the surface functions of enzymes can be used as to modulate enzyme-solid interactions and thereby influence bound enzyme behavior and (3) to investigate if sequestration of enzymes in the galleries of α-ZrP would enhance thermal stability due to decrease in the conformational entropy of the bound, unfolded state.

Enzyme binding to a model nanosolid, α--Zr(IV) phosphate has been examined in equilibrium binding studies, and bound enzyme properties have been examined by circular dichroism, absorption, and activity studies. Key properties of the bound enzymes have been compared with those of the corresponding free enzymes to access the influence of the solid support on bound enzyme behavior. The data have been used to test specific aspects of the enzyme-solid interactions and the mechanism of enzyme binding to solid surfaces.