Murine Extracellular Superoxide Dismutase Is Converted into the Inactive Fold by the Ser195Cys Mutation

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• 作者：Carsten Scavenius ; Jane S. Petersen ; Line R. Thomsen ; Ebbe Toftgaard Poulsen ; Zuzana Valnickova-Hansen ; Russell P. Bowler ; Tim D. Oury ; Steen V. Petersen ; Jan J. Enghild
• 刊名：Biochemistry
• 出版年：2013
• 出版时间：May 14, 2013
• 年：2013
• 卷：52
• 期：19
• 页码：3369-3375
• 全文大小：332K
• 年卷期：v.52,no.19(May 14, 2013)
• ISSN：1520-4995

文摘

We have previously shown that human extracellular superoxide dismutase (EC-SOD) exists as two variants with differences in their disulfide bridge patterns: one form is the active enzyme (aEC-SOD), and the other is inactive (iEC-SOD). The availability of both active and inactive folding variants significantly reduces the specific activity of EC-SOD in vivo. Both forms are produced during biosynthesis, but the underlying folding mechanisms remain unclear. To address this issue, we expressed EC-SOD in heterologous systems that do not endogenously express iEC-SOD. Rodents express only aEC-SOD because they lack Cys195 (human EC-SOD sequence numbering), which is essential for the formation of iEC-SOD. However, cultured hamster cells and transgenic mice expressing human EC-SOD were able to produce both human a- and iEC-SOD variants, which led us to hypothesize that the folding was sequence-dependent rather than a property of the expression system. To substantiate this hypothesis, we expressed murine EC-SOD in a human cell line, and as expected, only aEC-SOD was produced. Significantly, when Cys195 was introduced, both murine aEC-SOD and a novel murine iEC-SOD were generated, and the specific activity of the murine EC-SOD was significantly reduced by the mutation. Collectively, these data suggest that Cys195 actuates the formation of iEC-SOD, independent of the expression system or host. In addition, the dual-folding pathway most likely requires biosynthesis factors that are common to both humans and rodents.