Purification, crystallization and X-ray structures of two manganese superoxide dismutase from Caernohabditis elegans

Abstract

Caenorhabditis elegans expresses two manganese superoxide dismutase enzymes (MnSOD-2 andMnSOD-3) that are targeted to the mitochondrion. MnSOD-2 is constitutively expressed, while synthesis of MnSOD-3 is inducible. The structures of these two mononuclear metalloenzymes have been determined to 1.8 and 1.7 A ° resolution, respectively. Pink crystals formed in space group P41212 for each, with unit-cell parameters a = b = 81.0, c = 137.4 A ° forMnSOD-2 and a = b = 81.8, c = 136.0 A ° for MnSOD-3. The final structure of MnSOD-3 was refined to R = 21.6% and Rfree = 26.2% at 293 K, and R = 18.9% and Rfree = 22.6% at 100 K, while that of MnSOD-2 was refined to R = 16.9% and Rfree = 20.1% at 100 K. The asymmetric unit cell is comprised of two subunits. The resulting structures are very similar to that of human MnSOD and form a tetramer corresponding to a dimer of dimers. The subunit interface between dimers is comprised of two four-helix bundles that stabilize the biologically significant homotetramer.