Heme binding to the second, lower-affinity site of the global iron regulator Irr from Rhizobium leguminosarum promotes oligomerization.
Heme binding to the second, lower-affinity site of the global iron regulator Irr from Rhizobium leguminosarum promotes oligomerization.
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血红素与豆根瘤菌全局铁调节因子 Irr 的第二个亲和力较低的位点结合，可促进寡聚化。
DOI：
10.1111/j.1742-4658.2011.08117.x
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
White GF
中科院分区：
文献类型：
--
作者：
White GF
铁响应调节因子Irr存在于广泛的α-变形菌中，它调节许多基因以响应必需但有毒的金属铁。与几乎所有其他细菌谱系用于铁稳态的转录调节因子Fur不同，Irr不直接感测Fe 2+，而是与铁的生理学重要形式，即血红素相互作用。最近对来自固氮共生根瘤菌（Rhizobium leguminosarum，IrrRl）的Irr的研究表明，它以亚微摩尔亲和力在His-Xxx-His（HxH）基序上结合血红素。 这导致蛋白质与其同源DNA调节铁控制元件盒序列分离，从而允许其靶基因在铁充足条件下表达。在本研究中，我们报告了新的见解血红素结合Irr的机制和后果。除了HxH基序之外，Irr还在第二个较低亲和力的位点结合血红素。对野生型Irr和His变体的光谱研究表明，His 46和可能的His 66参与了在第二个位点以低自旋状态配位血红素。与来自慢生根瘤菌的已充分研究的Irr相比，IrrRl的两个血红素位点都不稳定亚铁血红素。 此外，我们表明，无血红素的IrrRlexists作为二聚体和更大的，可能是六聚体形式的混合物，并且血红素结合促进IrrRl寡聚化。IrrRl变体的生物分析研究表明，这种特性不依赖于HxH基序，而是与第二个位点的血红素结合有关。 通过分子筛作用结合到聚乙烯上（查看相互作用1，2）·Irr 在溶液中通过共沉淀结合到聚乙二醇（查看相互作用）
The iron responsive regulator Irr is found in a wide range of α‐proteobacteria, where it regulates many genes in response to the essential but toxic metal iron. Unlike Fur, the transcriptional regulator that is used for iron homeostasis by almost all other bacterial lineages, Irr does not sense Fe2+directly, but, rather, interacts with a physiologically important form of iron, namely heme. Recent studies of Irr from the N2‐fixing symbiontRhizobium leguminosarum(IrrRl) showed that it binds heme with submicromolar affinity at a His‐Xxx‐His (HxH) motif. This caused the protein to dissociate from its cognate DNA regulatory iron control element box sequences, thus allowing expression of its target genes under iron‐replete conditions. In the present study, we report new insights into the mechanisms and consequences of heme binding to Irr. In addition to the HxH motif, Irr binds heme at a second, lower‐affinity site. Spectroscopic studies of wild‐type Irr and His variants show that His46 and probably His66 are involved in coordinating heme in a low‐spin state at this second site. By contrast to the well‐studied Irr fromBradyrhizobium japonicum, neither heme site of IrrRlstabilizes ferrous heme. Furthermore, we show that heme‐free IrrRlexists as a mixture of dimeric and larger, likely hexameric, forms and that heme binding promotes IrrRloligomerization. Bioanalytical studies of IrrRlvariants showed that this property is not dependent on the HxH motif but is associated with heme binding at the second site.Structured digital abstract•Irr binds to irrby molecular sieving (View Interaction 1, 2)•Irr binds to irrby cosedimentation in solution (View interaction)