Characterization of the pH-dependent protein stability of 3α-hydroxysteroid dehydrogenase/carbonyl reductase by differential scanning fluorimetry.

The characterization of protein stability is essential for understanding the functions of proteins. Hydroxysteroid dehydrogenase is involved in the biosynthesis of steroid hormones and the detoxification of xenobiotic carbonyl compounds. However, the stability of hydroxysteroid dehydrogenases has not yet been characterized in detail. Here, we determined the changes in Gibbs free energy, enthalpy, entropy, and heat capacity of unfolding for 3α-hydroxysteroid dehydrogenase/carbonyl reductase (3α-HSD/CR) by varying the pH and urea concentration through differential scanning fluorimetry and presented pH-dependent protein stability as a function of temperature. 3α-HSD/CR shows the maximum stability of 30.79 kJ mol-1 at 26.4°C, pH 7.6 and decreases to 7.74 kJ mol-1 at 25.7°C, pH 4.5. The change of heat capacity of 30.25 ± 1.38 kJ mol-1 K-1 is obtained from the enthalpy of denaturation as a function of melting temperature at varied pH. Two proton uptakes are linked to protein unfolding from residues with differential pKa of 4.0 and 6.5 in the native and denatured states, respectively. The large positive heat capacity change indicated that hydrophobic interactions played an important role in the folding of 3α-HSD/CR. These studies reveal the mechanism of protein unfolding in HSD and provide a convenient method to extract thermodynamic parameters for characterizing protein stability using differential scanning fluorimetry.

[Structural Design and Finite Element Analysis of New Type Posterior Integral Glaucoma Valve].

The treatment of refractory Glaucoma is a difficult problem in clinical ophthalmology. For refractory glaucoma patients with hyphema, shallow anterior chamber, anterior conglutination of peripheral chamber angle, corneal endothelium dystrophy or decompensated, at present, there is no effective treatment. In order to solve this problem, a new type posterior integral glaucoma valve with IOP control device was designed using medical titanium alloy, and the valve model was established by Abaqus software, and the stiffness and preload of the valve were analyzed by finite element method. The results showed that the opening and closing of the valve were controlled automatically by the pressure difference between the front and back of the valve, and the opening and flow rate of the valve increase dynamically with the increase of intraocular pressure, and finally reached the set ideal IOP value of steady state.