Human glutathione transferase A3-3, a highly efficient catalyst of double-bond isomerization in the biosynthetic pathway of steroid hormones
Human glutathione transferase A3-3, a highly efficient catalyst of double-bond isomerization in the biosynthetic pathway of steroid hormones
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DOI：
10.1074/jbc.m104539200
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发表时间：
2001-08-31
影响因子：
4.8
通讯作者：
Mannervik, B
中科院分区：
文献类型：
--
作者：
Johansson, AS;Mannervik, B
克隆了一种新的α类人谷胱甘肽转移酶（GST）的cDNA，并异源表达了相应的蛋白质，命名为GST A3-3，并进行了表征。发现GST A3-3有效地催化δ（5）-雄甾烯-3，17-二酮和δ 5-雄甾烯-3，20-二酮（分别为睾酮和孕酮的前体）在类固醇激素生物合成中的强制性双键异构化。用δ（5）-雄甾烯-3，17-二酮的催化效率（k（cat）/K-m）测定为5 × 10（6）M-1 s（-1），这显著高于用任何其它测试的GST底物。基于k（cat）与Delta（5）-雄甾烯-3，17-二酮非酶异构化速率常数之间的比值，GST A3-3提供的加速速率为6 x 10（8）。除了绝对值高之外，GST A3-3的k（cat）/K-m值超过3 β-羟基类固醇脱氢酶/异构酶的k（cat）/K-m值约230倍，3 β-羟基类固醇脱氢酶/异构酶通常被认为催化Delta（5）-Delta（4）双键异构化。此外，GSTA 3特异性聚合酶链反应分析的cDNA文库从各种组织中显示的消息，只有在那些特征在于活跃的类固醇激素的生物合成，表明GST A3-3在这些组织中的选择性表达。基于这一发现和与类固醇底物的高活性，我们提出GST A3-3已经进化为催化异构化反应，有助于类固醇激素的生物合成。
The cDNA of a novel human glutathione transferase (GST) of the Alpha class was cloned, and the corresponding protein, denoted GST A3-3, was heterologously expressed and characterized. GST A3-3 was found to efficiently catalyze obligatory double-bond isomerizations of Delta (5)-androstene-3,17-dione and Delta5-pregnene-3,20-dione, precursors to testosterone and progesterone, respectively, in steroid hormone biosynthesis. The catalytic efficiency (k(cat)/K-m) with Delta (5)-androstene-3,17-dione was determined as 5 X 10(6) M-1 s(-1), which is considerably higher than with any other GST substrate tested. The rate of acceleration afforded by GST A3-3 is 6 x 10(8) based on the ratio between k(cat) and the rate constant for the nonenzymatic isomerization of Delta (5)-androstene-3,17-dione. Besides being high in absolute numbers, the k(cat)/K-m value of GST A3-3 exceeds by a factor of similar to 230 that of 3 beta -hydroxysteroid dehydrogenase/isomerase, the enzyme generally considered to catalyze the Delta (5)-Delta (4) double-bond isomerization. Furthermore, GSTA3-specific polymerase chain reaction analysis of cDNA libraries from various tissues showed a message only in those characterized by active steroid hormone biosynthesis, indicating a selective expression of GST A3-3 in these tissues. Based on this finding and the high activity with steroid substrates, we propose that GST A3-3 has evolved to catalyze isomerization reactions that contribute to the biosynthesis of steroid hormones.