The folding of human active and inactive extracellular superoxide dismutases is an intracellular event.

Abstract

Human extracellular superoxide dismutase (EC-SOD) is a tetrameric glycoprotein responsible for the removal of superoxide generated in the extracellular space. Two different folding variants of EC-SOD exist based on the disulfide bridge connectivity, resulting in enzymatically active (aEC-SOD) and inactive (iEC-SOD) subunits. As a consequence of this, the assembly of the EC-SOD tetramers produces molecules with variable activity and may represent a way to regulate the antioxidant level in the extracellular space. To determine whether the formation of these two folding variants is an intra- or extracellular event, we analyzed the biosynthesis in human embryonic kidney 293 cells expressing wild-type EC-SOD. These analyses revealed that both folding variants were present in the intra- and extracellular spaces, suggesting that the formation is an intracellular event. To further analyze the biosynthesis, we constructed mutants with the capacity to generate only aEC-SOD (C195S) or iEC-SOD (C45S). The expression of these suggested that the cellular biosynthetic machinery supported the secretion of aEC-SOD but not iEC-SOD. The coexpression of these two mutants did not affect the expression pattern. This study shows that generation of the EC-SOD folding variants is an intracellular event that depends on a free cysteine residue not involved in disulfide bonding.

DOI: 10.1074/jbc.M801548200

Cite this paper

@article{Petersen2008TheFO, title={The folding of human active and inactive extracellular superoxide dismutases is an intracellular event.}, author={Steen V Petersen and Torsten Kristensen and Jane S Petersen and Lasse Ramsgaard and Tim D Oury and James D Crapo and Niels C Nielsen and Jan J Enghild}, journal={The Journal of biological chemistry}, year={2008}, volume={283 22}, pages={15031-6} }