Strengthening the Stability of a Tunnel-Shaped Homotetramer Protein with Nanogels

Urate oxidase (UOX, EC 1.7.3.3) is effective for the treatment of gout and hyperuricaemia associated with tumor lysis syndrome. The inherent poor stability of UOX to temperature, proteolysis, and acidic environments is known to limit its efficacy. Herein, we encapsulated UOX into spherical and porous nanogels with diameters of 20–40 nm via a two-step in situ polymerization in the presence of oxonic acid potassium salt, an inhibitor of UOX. The UOX nanogel retained 70% of the initial activity but showed an expanded pH spectrum from pH 6–10 to 3–10 and an extended half-life at 37 °C from 5 min to 3 h. The enhanced pH stability, thermal stability, and enzyme resistance of the UOX nanogels were also confirmed by using fluorescence spectroscopy and enzymatic digestion. A molecular dynamics simulation was performed as a way to probe the mechanism underlying the formation of UOX nanogels as well as the strengthened stability against harsh conditions. It was shown that the encapsulation into the polyacrylamide network reinforced the intersubunit hydrogen bonding, shielded the hydrolytic reaction site, and thus protected the tertiary and quaternary structure of UOX. The UOX nanogel with enhanced stability provided a stable enzyme model that enables the exploration of UOX in the diagnosis and therapy of disorders associated with altered purine metabolism.