Effect of metal ions on the secondary structure of PdeM.

(A) Effect of increasing Mn²⁺ ions on the Circular Dichroism (CD) spectra of PdeM recorded in the far-UV region (from 200 to 260 nm) at 25°C at a protein concentration of 5 μM in 10 mM phosphate buffer (pH 7.0). (B) Effect of increasing concentrations of Mn²⁺ ions on the secondary structural elements (α-helix and β-sheets). (C) Effect of increasing concentrations of Fe³⁺ ions on the CD spectra of PdeM protein recorded in the far-UV region at a concentration of 4.11 μM PdeM in 10mM phosphate buffer (pH 7.0). (D) Effect of increasing concentrations of Fe³⁺ ions on the secondary structural elements (α-helix and β-sheets). The spectra reported are representative from of the three independent experiments. (E) Effect of temperature on the ellipticity of PdeM analyzed by CD spectroscopy in the absence of Mn²⁺ ions. (F) The thermal melting profile of PdeM monitored in the absence of Mn²⁺ ions by CD signals at 222 nm. (G) Effect of temperature on the ellipticity of PdeM analyzed by CD spectroscopy in the presence of 3 mM Mn²⁺ ions. (H) The thermal melting profile of PdeM monitored in the presence of 3 mM Mn²⁺ ions by CD signals at 222 nm. The temperature of the enzyme solution (8 μM) in the cell was gradually increased in a step-wise manner from 20°C to 80°C. The CD signals were recorded after equilibrating the cell for at least 5 min, after each desired temperature was attained.