Structure-activity characterization of sulfide:quinone oxidoreductase variants
Structure-activity characterization of sulfide:quinone oxidoreductase variants
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DOI：
10.1016/j.jsb.2012.04.007
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发表时间：
2012-06-01
影响因子：
3
通讯作者：
Weiner, Joel H.
中科院分区：
文献类型：
--
作者：
Cherney, Maia M.;Zhang, Yanfei;Weiner, Joel H.
硫化物：醌氧化还原酶（SQR）是一种外周膜蛋白，催化硫化物氧化为元素硫。酶促反应分两步进行。来自硫化物的电子首先转移到酶辅因子FAD，FAD又将它们传递到膜中的醌池上。最近已经报道了几种野生型SQR结构。然而，SQR的酶促机制尚未完全阐明。为了了解催化必需残基在SQR的酶促机制中的作用，我们在催化位点中产生了许多保守残基的变体，包括来自嗜酸性、化学无机营养细菌Acidithiobacillus ferrooxidans的SQR的半胱氨酸三联体。对这些化合物进行了结构表征，并测定了它们在每个反应步骤中的活性。此外，野生型SQR与硒化钠和氰化金（I）的晶体结构已被确定。以前我们提出了一个机制，为减少硫化物元素硫涉及亲核攻击Cys 356对C-4A原子的FAD。在这里，我们还考虑了一个替代的阴离子自由基的机制，通过直接电子转移从Cys 356的异咯嗪环的FAD。(c)2012 Elsevier Inc. All rights reserved.
Sulfide:quinone oxidoreductase (SQR) is a peripheral membrane protein that catalyzes the oxidation of sulfide species to elemental sulfur. The enzymatic reaction proceeds in two steps. The electrons from sulfides are transferred first to the enzyme cofactor, FAD, which, in turn, passes them onto the quinone pool in the membrane. Several wild-type SQR structures have been reported recently. However, the enzymatic mechanism of SQR has not been fully delineated. In order to understand the role of the catalytically essential residues in the enzymatic mechanism of SQR we produced a number of variants of the conserved residues in the catalytic site including the cysteine triad of SQR from the acidophilic, chemolithotrophic bacterium Acidithiobacillus ferrooxidans. These were structurally characterized and their activities for each reaction step were determined. In addition, the crystal structures of the wild-type SQR with sodium selenide and gold(I) cyanide have been determined. Previously we proposed a mechanism for the reduction of sulfides to elemental sulfur involving nucleophilic attack of Cys356 on C-4A atom of FAD. Here we also consider an alternative anionic radical mechanism by direct electron transfer from Cys356 to the isoalloxazine ring of FAD. (c) 2012 Elsevier Inc. All rights reserved.