Influence Of Au Nanoparticle Size And Coverage On Enzymatic Structure And Activity Of GOD

The protein adsorption on nanoparticles (NPs) forms the protein-nanoparticles bioconjugates by physical and chemical processes. The attachment of NPs to proteins has found applications in biosensor, in imaging, in catalysis, in delivery and in the study of protein structure and function. The protein structure can be affected by the topological structures of nanoparticles, such as, surface curvature, surface roughness, surface morphology. This can lead to the changes of protein activity. Common nanoparticles include AuNPs, AgNPs and hydrophilic or hydrophobic silica nanoparticles (SNPs), etc. And common proteins are small including Lysozyme, Cytochrome C, Bovine Serum Albumin (BSA) and Fungal Protease, etc. However, a dimeric and large protein as model protein is rarely reported.Glucose oxidase (GOD) as a dimeric and large protein, is widely used in food, feed, medicine and biosensor. GOD found in 1904 was used as the model protein, which was well-studied.This work has mainly studied the effects of size and coverage of "bare" AuNPs on the structure and activity of GOD. AuNPs with different sizes were synthesized by seeding growth methods using Hydroxylamine Hydrochloride or Ascorbic acid as reductants. The effects of different reductants on the morphology, particle size and monodispersity of products were investigated. When the surface coverage of GOD on AuNPs is 80%, the structure and activity of GOD on AuNPs of different sizes have been studied. What is more, effects of surface coverage on the structure and activity of GOD have been studied.The mian results are showen as below.(1) The monodispersity of AuNPs synthesized by seeding growth methods using Hydroxylamine Hydrochloride was better than that of Ascorbic acid. Seeding growth methods should avoid the secondary core. Peak width at half max (PWHM) could be used to compare the monodispersity of AuNPs synthesized using the same method, but not using different methods.(2) With the surface coverage of 80%, GOD underwent significant perturbation of secondary structure and microenvironment of Flavin adenine dinucleotide (FAD) upon adsorption on AuNPs, which was strongly dependent upon the size of nanoparticles. Adsorption of GOD onto 13 nm AuNPs (the smallest particle in this study) resulted in the loss of a-helix content. And with AuNPs size increasing, the a-helix content of adsorbed GOD increased. With AuNPs size increasing, tryptophan residues exhibited movement towards more polar environment and the perturbation of the FAD microenvironment becomed larger and larger; however, for 52 nm and 76 nm AuNPs, the changes were almost similar. The activity of GOD adsorbed on 13 nm AuNPs was inhibited and adsorption of GOD to AuNPs leaded to a size-dependent increase of GOD activity. When the surface coverage of GOD on AuNPs increased, the activity of GOD on 13 nm AuNPs decreased.