A Single Mutation is Sufficient to Modify the Metal Selectivity and Specificity of a Eukaryotic Manganese Superoxide Dismutase to Encompass Iron

We have generated a site‐directed mutant of the manganese superoxide dismutase SOD‐3 of C.elegans (MnSOD‐3) which modifies the metal specificity of the enzyme. While wild‐type MnSOD‐3 functions with manganese in the active site (3600 U mg−1 of protein) it has little or no activity when iron is incorporated. However, when histidine replaces glutamine 142 in the active site, the enzyme retains 50 % of its activity and becomes cambialistic for its metal cofactor exhibiting very similar specific activity with either manganese or iron

Substitution of histidine 30 by asparagine in manganese superoxide dismutase alters biophysical properties and supports proliferation in a K562 leukemia cell line.

We have generated a mutant of C. elegans manganese superoxide dismutase at histidine 30 by site-directed mutagenesis. The structure was solved at a resolution of 1.52 Å by X-ray crystallography (pdb: 6S0D). His30 was targeted, as it forms as a gateway residue at the top of the solvent access funnel to the active site, together with Tyr34. In the wild-type protein, these gateway residues are involved in the hydrogen-bonding network providing the protons necessary for the catalytic reaction at the metal center. However, biophysical characterization and cell viability experiments reveal that a mutation from histidine to asparagine in the H30N mutant modifies metal selectivity in the protein, favoring the uptake of iron over manganese in minimal media conditions, alters active-site coordination from the characteristic trigonal bipyramidal to octahedral geometry, and encourages cellular proliferation in K562 cells, when added exogenously to the cells