Expression of human Cu, Zn-superoxide dismutase in an insect cell-free system and its structural analysis by MALDI-TOF MS.

Human Cu, Zn-superoxide dismutase (hSOD1) is a homodimer that coordinates one copper and one zinc ion per monomer. These metal ions contribute to its enzymatic activity and structural stability. In addition, hSOD1 maintains an intra-subunit disulfide bond formed in the reducing environment of the cytosol and is active under a variety of stringent denaturing conditions. We report the expression of hSOD1 in a cell-free protein synthesis system constructed from Spodoptera frugiperda 21 (Sf21) insect cells, and its structural analysis including the status of the sole intra-subunit disulfide bond by mass spectrometry. By using this system hSOD1 was obtained in a soluble active form after addition of Cu(2+) and Zn(2+) and was purified with a yield of approximately 33 microg from 1 ml of reaction volume. Both enzymatic and structural analyses of the recombinant hSOD1 indicate that it was completely identical to the protein isolated from human erythrocytes.