Cofacial heme binding is linked to dimerization by a bacterial heme transport protein
Cofacial heme binding is linked to dimerization by a bacterial heme transport protein
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DOI：
10.1016/j.jmb.2006.08.001
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发表时间：
2006-10-06
影响因子：
5.6
通讯作者：
Murphy, Michael E. P.
中科院分区：
文献类型：
--
作者：
Chan, Anson C. K.;Lelj-Garolla, Barbara;Murphy, Michael E. P.
在发达国家，空肠弯曲杆菌是引起食源性疾病的主要细菌。像大多数病原体一样，空肠梭菌需要铁，而铁必须从宿主环境中获得。虽然食源性病原体空肠梭菌对铁的偏好尚未确定，但这种生物具有血红素运输系统来获取铁。ChaN是一种来自空肠梭菌的铁调控脂蛋白，被认为与外膜受体ChaR有关。铜绿假单胞菌中ChaN同源物PhuW的突变，影响了血红素作为唯一铁源的生长。以1.9 A分辨率测定的ChaN晶体结构表明，ChaN由一个大的平行β片和一个由α -螺旋组成的小结构域组成。出乎意料的是，两个共面血红素基团（相距3.5埃，铁间距离4.4埃）结合在由ChaN单体二聚体形成的口袋中。每个血红素铁由来自一个单体的单个酪氨酸配位，丙酸基团由来自另一个单体的组氨酸和赖氨酸氢键连接。序列分析表明，这些残基在不同细菌来源的ChaN同源物中是保守的。电子吸收和电子顺磁共振（EPR）谱分析结果表明，在溶液中，ChaN通过酪氨酸配位与血红素结合，产生了高自旋的血红素铁结构，与低自旋的物质呈ph依赖平衡。分析性超离心表明，载脂蛋白chan主要是单体和二聚化。与血红素结合时发生，使二聚体形成的稳定常数增加60倍。(c) 2006 Elsevier Ltd.版权所有。
Campylobacter jejuni is a leading bacterial cause of food-borne illness in the developed world. Like most pathogens, C. jejuni requires iron that must be acquired from the host environment. Although the iron preference of the food-borne pathogen C. jejuni is not established, this organism possesses heme transport systems to acquire iron. ChaN is an iron-regulated lipoprotein from C. jejuni proposed to be associated with ChaR, an outermembrane receptor. Mutation of PhuW, a ChaN orthologue in Pseudomonas aerugmosa, compromises growth on heme as a sole iron source. The crystal structure of ChaN, determined to 1.9 A resolution reveals that ChaN is comprised of a large parallel beta-sheet with flanking alpha-helices and a smaller domain consisting of alpha-helices. Unexpectedly, two cofacial heme groups (similar to 3.5 angstrom apart with an inter-iron distance of 4.4 angstrom) bind in a pocket formed by a dimer of ChaN monomers. Each heme iron is coordinated by a single tyrosine from one monomer, and the propionate groups are hydrogen bonded by a histidine and a lysine from the other monomer. Sequence analyses reveal that these residues are conserved among ChaN homologues from diverse bacterial origins. Electronic absorption and electron paramagnetic resonance (EPR) spectroscopy are consistent with heme binding through tyrosine coordination by ChaN in solution yielding a high-spin heme iron structure in a pH-dependent equilibrium with a low-spin species. Analytical ultracentrifugation demonstrates that apo-ChaN is predominantly monomeric and that dimerization. occurs with heme binding such that the stability constant for dimer formation increases by 60-fold. (c) 2006 Elsevier Ltd. All rights reserved.