4.1.2. Enzyme Orientation on the Surface

Upon immobilization of an enzyme onto a support, several processes are going to take place: change in the state of hydration of the enzyme surface, enzyme structural rearrangements, redistribution of charge groups, or surface aggregation [115]. These are slow processes since they involve a whole cascade of rotations. While proteins can rotate freely in solution, they will adopt on a surface one preferential orientation that exposes one part of the enzyme to the surface and the other part to the bulk solution. However, the final orientation can be very different from requirements for optimal activity. Favored orientation is linked to the minimum free energy resulting from attractive coulomb and van der Waals interactions, hydrogen bonds, and the entropy gain of solvent molecules or counter ion release [115]. In addition, rotation of the enzyme can occur even in the adsorption state when local conditions change [116]. In the case of immobilized enzyme, it was expected that only the amino acids on the surface of the enzyme will sense the support. However, by looking at the rigidity profile obtained by Brownian dynamics simulations, it was very recently shown that even amino acids in the core of the enzyme can be affected depending on the surface charge of the support [117].
