pH-Induced Conformational Change of IscU at Low pH Correlates with Protonation/Deprotonation of Two Conserved Histidine Residues
pH-Induced Conformational Change of IscU at Low pH Correlates with Protonation/Deprotonation of Two Conserved Histidine Residues
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DOI：
10.1021/bi500313t
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发表时间：
2014-08-19
期刊：
影响因子：
2.9
通讯作者：
Markley, John L.
中科院分区：
文献类型：
--
作者：
Dai, Ziqi;Kim, Jin Hae;Markley, John L.
IscU 是微生物和线粒体中主要铁硫簇生物合成途径（ISC 途径）的支架蛋白，在 [2Fe-2S] 和 [4Fe-4S] 簇的形成及其向受体脱辅基蛋白的递送中发挥重要作用。我们的实验室表明，IscU 具有两种不同的、功能相关的构象状态，一种更结构化的状态 (S) 和一种更动态的状态 (D)，其区别在于两个肽基-脯氨酰肽键的顺式/反式异构化 [Kim, J. H.、Tonelli, M. 和 Markley, J. L. (2012) Proc.国家。阿卡德。科学。美国，109，454-459。 Dai Z.、Tonelli, M. 和 Markley, J. L. (2012) 生物化学, 51, 9595-9602。 Cai, K.、Frederick, R. O.、Kim, J. H.、Reinen, N.M.、Tonelli, M. 和 Markley, J. L. (2013) J. Biol。 Chem., 288, 28755-28770] 在这里，我们报告了关于大肠杆菌 IscU 的 D-S 平衡的 pH 依赖性的发现，其中 D-状态在低和高 pH 值下稳定。我们表明，pH 依赖曲线的下半部分是由两种状态下两个保守组氨酸残基（His10 和 His105）的 pK(a) 值差异造成的。在 D 态下，His 10 的净质子亲和力比在 S 态下高约 SO 倍，而 His 105 的净质子亲和力则高 13 倍。 D S pH 依赖性高边的起源仍有待确定。这些结果表明，在涉及 IscU 在 S 态和 D 态之间转变的铁硫簇组装和转移步骤中，需要考虑质子库存的变化。
IscU, the scaffold protein for the major iron-sulfur cluster biosynthesis pathway in microorganisms and mitochondria (ISC pathway), plays important roles in the formation of [2Fe-2S] and [4Fe-4S] clusters and their delivery to acceptor apo-proteins. Our laboratory has shown that IscU populates two distinct, functionally relevant conformational states, a more structured state (S) and a more dynamic state (D), that differ by cis/trans isomerizations about two peptidyl-prolyl peptide bonds [Kim, J. H., Tonelli, M., and Markley, J. L. (2012) Proc. Natl. Acad. Sci. U.S.A., 109, 454-459. Dai Z., Tonelli, M., and Markley, J. L. (2012) Biochemistry, 51, 9595-9602. Cai, K., Frederick, R. O., Kim, J. H., Reinen, N. M., Tonelli, M., and Markley, J. L. (2013) J. Biol. Chem., 288, 28755-28770] Here, we report our findings on the pH dependence of the D S equilibrium for Escherichia coli IscU in which the D-state is stabilized at low and high pH values. We show that the lower limb of the pH dependence curve results from differences in the pK(a) values of two conserved histidine residues (His10 and His105) in the two states. The net proton affinity of His 10 is about SO times higher and that of His 105 is 13 times higher in the D-state than in the S-state. The origin of the high limb of the D S pH dependence remains to be determined. These results show that changes in proton inventory need to be taken into account in the steps in iron-sulfur cluster assembly and transfer that involve transitions of IscU between its S- and D-states.