Manganese superoxide dismutase from human pathogen Clostridium difficile.

Clostridium difficile is a human pathogen that causes severe antibiotic-associated Clostridium difficile infection (CDI). Herein the MnSODcd from C. difficile was cloned, expressed in Escherichia Coli,and characterized by X-ray crystallography, UV/Vis and EPR spectroscopy, and activity assay, et al. The crystal structure of MnSODcd (2.32 Å) reveals a manganese coordination geometry of distorted trigonal bipyramidal, with His111, His197 and Asp193 providing the equatorial ligands and with His56 and a hydroxide or water forming the axial ligands. The catalytic activity of MnSODcd (8,600 U/mg) can be effectively inhibited by 2-methoxyestradiol with an IC50 of 75 μM. The affinity investigation between 2-methoxyestradiol and MnSODcd by ITC indicated a binding constant of 8.6 μM with enthalpy changes (ΔH = -4.08 ± 0.03 kcal/mol, ΔS = 9.53 ± 0.02 cal/mol/deg). An inhibitory mechanism of MnSODcd by 2-methoxyestradiol was probed and proposed based on molecular docking models and gel filtration analysis. The 2-methoxyestradiol may bind MnSODcd to interfere with the cross-linking between the two active sites of the dimer enzyme, compromising the SOD activity. These results provide valuable insight into the rational design of MnSODcd inhibitors for potential therapeutics for CDI.