Protected Sulfur Transfer Reactions by the Escherichia coli Suf System
Protected Sulfur Transfer Reactions by the Escherichia coli Suf System
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DOI：
10.1021/bi4001479
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发表时间：
2013-06-11
期刊：
影响因子：
2.9
通讯作者：
Dos Santos, Patricia C.
中科院分区：
文献类型：
--
作者：
Selbach, Bruna P.;Pradhan, Pradyumna K.;Dos Santos, Patricia C.
在大肠杆菌氧化应激和铁饥饿下，硫动员生物合成 Fe-S 簇的第一步涉及半胱氨酸脱硫酶 SufS。其催化反应性取决于硫受体蛋白 SufE 的存在，SufE 是该酶的首选底物。对部分受到还原剂（例如二硫苏糖醇和谷胱甘肽）保护的大肠杆菌 SufS 的半胱氨酸：SufE 硫转移酶反应进行了动力学分析。在这些条件下，反应显示出双相曲线，其中第一相涉及从 SufS 到 SufE 的快速硫转移反应。 SufE 的过硫化/多硫化形式的积累是缓慢催化周转率的第二阶段的原因。 SufBCD复合物的存在增强了与第二相相关的活性，同时适度抑制了与初始硫从SufS转移到SufE相关的活性。因此，硫从 SufS 转移到最终提出的 SufBCD Fe-S 簇支架的速率似乎取决于最终硫受体的可用性。使用更强的还原剂[三(2-羧乙基)膦盐酸盐]引发了SufS-SufE反应的最大活性并超过了SufBCD的刺激作用。这种协调的硫运输路径涉及从 SufS 到 SufE 再到 SufBCD 的顺序转移，保证了以受控通量保护中间体，以满足在不利于硫醇化学和 Fe-S 簇代谢的条件下遇到的细胞需求。
The first step in sulfur mobilization for the biosynthesis of Fe-S clusters under oxidative stress and iron starvation in Escherichia coli involves a cysteine desulfurase SufS. Its catalytic reactivity is dependent on the presence of a sulfur acceptor protein, SufE, which acts as the preferred substrate for this enzyme. Kinetic analysis of the cysteine:SufE sulfurtransferase reaction of the E. coli SufS that is partially protected from reducing agents, such as dithiothreitol and glutathione, was conducted. Under these conditions, the reaction displays a biphasic profile in which the first phase involves a fast sulfur transfer reaction from SufS to SufE. The accumulation of persulfurated/polysulfurated forms of SufE accounts for a second phase of the slow catalytic turnover rate. The presence of the SufBCD complex enhances the activity associated with the second phase, while modestly inhibiting the activity associated with the initial sulfur transfer from SufS to SufE. Thus, the rate of sulfur transfer from SufS to the final proposed SufBCD Fe-S cluster scaffold appears to be dependent on the availability of the final sulfur acceptor. The use of a stronger reducing agent [tris(2-carboxyethyl)phosphine hydrochloride] elicited the maximal activity of the SufS-SufE reaction and surpassed the stimulatory effect of SufBCD. This concerted sulfur trafficking path involving sequential transfer from SufS to SufE to SufBCD guarantees the protection of intermediates at a controlled flux to meet cellular demands encountered under conditions detrimental to thiol chemistry and Fe-S cluster metabolism.