Structural Insight into the Heme-based Redox Sensing by DosS from Mycobacterium tuberculosis
Structural Insight into the Heme-based Redox Sensing by DosS from Mycobacterium tuberculosis
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DOI：
10.1074/jbc.m808905200
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发表时间：
2009-05-08
影响因子：
4.8
通讯作者：
Kang, Beom Sik
中科院分区：
文献类型：
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作者：
Cho, Ha Yeon;Cho, Hyo Je;Kang, Beom Sik
结核分枝杆菌被认为在缺氧或一氧化氮（NO）的影响下转化为非复制持续状态。这种转化被认为是通过两个传感器组氨酸激酶，DoS和DoS T，其中每一个包含两个GAF结构域，负责检测氧张力介导的。在这项研究中，我们确定了第一GAF域（GAF-A）的DoS，这表明与血红素的相互作用的晶体结构。b型血红素嵌入在GAF-A结构域的疏水空腔中，并且大致垂直于GAF结构域的β折叠。His-149在近端血红素轴位与血红素铁配体结合。铁，在氧化的形式，是六配位的水分子在远端的位置。在还原时，亚铁形式的铁是五配位的，并且当GAF结构域暴露于大气O-2时，亚铁形式被氧化以生成Met形式而不是亚铁O-2结合形式。由于血红素在GAF域中是孤立的，因此其可访问性受到限制。然而，在血红素位点发现的确定的氢键网络可以加速电子转移性，并解释了为什么DoS不能结合O-2。黄素核苷酸被证明可以减少DoS的血红素铁，而NADH不能这样做。这些结果表明，DoS是一种氧化还原传感器，并通过其还原检测缺氧条件。
Mycobacterium tuberculosis is thought to undergo transformation into its non-replicating persistence state under the influence of hypoxia or nitric oxide (NO). This transformation is thought to be mediated via two sensor histidine kinases, DosS and DosT, each of which contains two GAF domains that are responsible for detecting oxygen tension. In this study we determined the crystal structures of the first GAF domain (GAF-A) of DosS, which shows an interaction with a heme. A b-type heme was embedded in a hydrophobic cavity of the GAF-A domain and was roughly perpendicular to the beta-sheet of the GAF domain. The heme iron was liganded by His-149 at the proximal heme axial position. The iron, in the oxidized form, was six-coordinated with a water molecule at the distal position. Upon reduction, the iron, in ferrous form, was five-coordinated, and when the GAF domain was exposed to atmospheric O-2, the ferrous form was oxidized to generate the Met form rather than a ferrous O-2-bound form. Because the heme is isolated inside the GAF domain, its accessibility is restricted. However, a defined hydrogen bond network found at the heme site could accelerate the electron transferability and would explain why DosS was unable to bind O-2. Flavin nucleotides were shown to reduce the heme iron of DosS while NADH was unable to do so. These results suggest that DosS is a redox sensor and detects hypoxic conditions by its reduction.