Effect of particle size and surface linkers of SiO2 nanoparticles on the efficiency of human tyrosine hydroxylase

Abstract Tyrosine hydroxylase (hTH) catalyzes the conversion of l -tyrosine to l -DOPA, the rate-limiting step in dopamine biosynthesis. As impaired hTH function is implicated in dopamine-related neurodegenerative disorders, conventional therapies relying on l -DOPA supplementation often cause adverse side effects. In this study, we investigate the immobilization of recombinant hTH onto silica nanoparticles (SNPs) as a molecularly engineered platform for enzyme replacement therapy (ERT) via intranasal administration. Recombinant GST-tagged hTH was expressed in E. coli with high yield and purity, while SNPs were synthesized with controlled size distribution and surface functionalization to enable efficient ionic binding. Immobilization efficiencies exceeding 70% were achieved. Dynamic light scattering and ζ-potential measurements confirmed enhanced colloidal stability and a reduction in protein aggregation upon immobilization. Enzymatic assays based on dopachrome formation demonstrated that catalytic activity was preserved post-immobilization. Collectively, these findings highlight SNP-based immobilization as a promising liquid-phase nanobiotechnological approach, offering a stable and non-invasive therapeutic platform for dopamine-related pathologies. • The particle size of SiO2 nanoparticle influence their hTH binding efficiency. • The SiO2 binding reduces hTH aggregation and enhance structural integrity. • Amino-linker density of nanoparticles directly affects hTH enzyme activity. • Electrostatic interactions allow homogenous enzyme coverage on nanoparticle. • The SiO2 particle size has optimum on specific enzyme activity.