Kennedy M C, Mende-Mueller L, Blondin G A, Beinert H
Department of Biochemistry, Medical College of Wisconsin, Milwaukee 53226.
Proc Natl Acad Sci U S A. 1992 Dec 15;89(24):11730-4. doi: 10.1073/pnas.89.24.11730.
In recent reports attention has been drawn to the extensive amino acid homology between pig heart, yeast, and Escherichia coli aconitases (EC 4.2.1.3) and the iron-responsive element binding protein (IRE-BP) of mammalian cells [Rouault, T. A., Stout, C. D., Kaptain, S., Harford, J. B. & Klausner, R. D. (1991) Cell 64, 881-883.; Hentze, M. W. & Argos, P. (1991) Nucleic Acids Res. 19, 1739-1740.; Prodromou, C., Artymiuk, P. J. & Guest, J. R. (1992) Eur. J. Biochem. 204, 599-609]. Iron-responsive elements (IREs) are stem-loop structures located in the untranslated regions of mRNAs. IRE-BP is required in the posttranscriptional regulation of ferritin mRNA translation and stabilization of transferrin receptor mRNA. In spite of substantial homology between the amino acid sequences of mammalian mitochondrial aconitase and IRE-BP, the mitochondrial protein does not bind IREs. However, there is a second aconitase, found only in the cytosol of mammalian tissues, that might serve as an IRE-BP. To test this possibility, we have prepared sufficient quantities of the heretofore poorly characterized beef liver cytosolic aconitase. This enzyme is isolated largely in its active [4Fe-4S] form and has a turnover number similar to that of mitochondrial aconitase. The EPR spectra of the two enzymes are markedly different. The amino acid composition, molecular weight, isoelectric point, and the sequences of six random peptides clearly show that these physicochemical and structural characteristics are identical to those of IRE-BP, and that c-aconitase is distinctly different from m-aconitase. In addition, both cytosolic aconitase and IRE-BP can have aconitase activity or function as IRE-BPs, as shown in the following paper and elsewhere [Zheng, L. Kennedy, M. C., Blondin, G. A., Beinert, H. & Zalkin, H. (1992) Arch. Biochem. Biophys., in press]. This leads us to the conclusion that cytosolic aconitase is IRE-BP.
在最近的报道中，猪心脏、酵母和大肠杆菌顺乌头酸酶（EC 4.2.1.3）与哺乳动物细胞的铁反应元件结合蛋白（IRE - BP）之间广泛的氨基酸同源性已引起关注[鲁奥尔特，T.A.，斯托特，C.D.，卡普坦，S.，哈福德，J.B.和克劳斯纳，R.D.（1991年）《细胞》64卷，881 - 883页；亨策，M.W.和阿戈斯，P.（1991年）《核酸研究》19卷，1739 - 1740页；普罗德罗莫，C.，阿蒂缪克，P.J.和格斯特，J.R.（1992年）《欧洲生物化学杂志》204卷，599 - 609页]。铁反应元件（IREs）是位于mRNA非翻译区的茎环结构。IRE - BP在铁蛋白mRNA翻译的转录后调控和转铁蛋白受体mRNA的稳定中是必需的。尽管哺乳动物线粒体顺乌头酸酶和IRE - BP的氨基酸序列有大量同源性，但线粒体蛋白并不结合IREs。然而，有一种仅在哺乳动物组织胞质溶胶中发现的第二种顺乌头酸酶，它可能作为IRE - BP起作用。为了验证这种可能性，我们制备了足够量的此前表征不佳的牛肝脏胞质溶胶顺乌头酸酶。这种酶主要以其活性[4Fe - 4S]形式分离出来，其周转数与线粒体顺乌头酸酶相似。这两种酶的电子顺磁共振光谱明显不同。氨基酸组成、分子量、等电点以及六个随机肽段的序列清楚地表明，这些物理化学和结构特征与IRE - BP的相同，并且胞质溶胶顺乌头酸酶（c - aconitase）与线粒体顺乌头酸酶（m - aconitase）明显不同。此外，如下文及其他地方所示[郑，L.肯尼迪，M.C.，布朗丁，G.A.，贝纳特，H.和扎尔金，H.（1992年）《生物化学与生物物理学报》，即将发表]，胞质溶胶顺乌头酸酶和IRE - BP都可以具有顺乌头酸酶活性或作为IRE - BP发挥作用。这使我们得出结论：胞质溶胶顺乌头酸酶就是IRE - BP。
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