(560il) Molecular Dynamics Simulation of Graphene Oxide-Enzyme Assembly for Gaseous Catalysis

Gaseous enzymatic catalysis holds great promise for chemical synthesis but is not yet applied due mainly to the water content dilemma. On one hand, an enzyme in dry state is stable but not active because of hindered conformational transition. On the other hand, a wetted enzyme may appear a high activity but is less stable because of water attack through hydrogen bond exchanging between surface amino residues with free water molecules in the moisture. We have proposed an idea of using graphene oxide (GO) to form enzyme aerogel, in which GO provides a hydrophilic microenvironment required for enzyme catalysis, and demonstrated its effectiveness in using Candida antarctica lipase B (CALB) as an example. In this study, we use molecular dynamics simulation to probe the assembly of GO and CALB and illustrate how GO stabilizes the active conformation of CALB in anhydrous status. Three kinds of GO sheets with different oxygen content were tested, in which a simulated annealing procedure was applied to accelerate the assembly process. It is shown that a higher oxygen content of GO intensifies its interaction with CALB via generating more intermolecular hydrogen bonds. The presence of GO reduces the intermolecular hydrogen bond between CALB and water, indicating the replacement of surface water molecules, terms as essential water, as observed by TGA analysis. Moreover,the presence of GO made the secondary structure of the CALB closer to its native form in the aqueous phase, this is favorable for the catalysis where the enzyme conformation transition is required. These simulation results offer a molecular insight into GO-CALB aerogel, which is essential to the design of GO-enzyme aerogel for gaseous enzymatic catalysis.