Sugawara T, Nomura E, Hoshi N
Department of Biochemistry, Hokkaido Graduate School of Medicine, Nishi, Sapporo, Japan.
J Endocrinol. 2006 Feb;188(2):365-74. doi: 10.1677/joe.1.06417.
Steroid sulfatase (STS) is localized in the endoplasmic reticulum and catalyzes desulfation of 3beta-hydroxysteroid sulfates. X-linked ichthyosis (XLI) is an inherited skin disorder caused by deficiency of STS enzyme activity. We previously reported a case in which XLI with a one-base change in the STS gene and variation in amino acid Q560P developed. In this study, we performed molecular analysis to determine the importance of terminal regions of STS and the effect of mutant STS on STS enzyme activity. To examine the effect of terminal truncated STS on the enzyme activity, N- and C-terminal truncated STS expression vectors were transfected into COS-1 cells. The activity of truncated STS lacking the N-terminal regions declined, and the activity of C-terminal-truncated STS declined with extension of the truncated C-terminal region. Although the results of pulse-chase experiments showed that a one-base mutant STS (Q560P) and C-terminal-truncated STS (deltaC2 (1-559)) had no effects on protein synthesis and degradation, the mutant STS and C-terminal-truncated STS have dominant negative effect on STS enzyme activity when the STS mutant or truncated STS protein and a wild-type STS protein coexist in cells. Results of coprecipitation of the truncated STS with an STS-FLAG fusion protein showed that STS formed a dimer conformation in cells. In this study, we have shown that both the N-terminal region and C-terminal region are important for STS enzyme activity. The C-terminal mutant has a dominant negative effect on wild-type STS.
类固醇硫酸酯酶（STS）定位于内质网，催化3β-羟基类固醇硫酸盐的脱硫酸反应。X连锁鱼鳞病（XLI）是一种由STS酶活性缺乏引起的遗传性皮肤病。我们之前报道过一例XLI病例，该病例中STS基因发生单碱基变化且氨基酸出现Q560P变异。在本研究中，我们进行了分子分析，以确定STS末端区域的重要性以及突变型STS对STS酶活性的影响。为了检测末端截短的STS对酶活性的影响，将N端和C端截短的STS表达载体转染到COS-1细胞中。缺失N端区域的截短型STS活性下降，C端截短型STS的活性随着截短的C端区域延长而下降。尽管脉冲追踪实验结果表明单碱基突变型STS（Q560P）和C端截短型STS（deltaC2 (1 - 559)）对蛋白质合成和降解没有影响，但当STS突变体或截短型STS蛋白与野生型STS蛋白在细胞中共存时，突变型STS和C端截短型STS对STS酶活性具有显性负效应。截短型STS与STS-FLAG融合蛋白的共沉淀结果表明，STS在细胞中形成二聚体构象。在本研究中，我们表明N端区域和C端区域对STS酶活性都很重要。C端突变体对野生型STS具有显性负效应。
