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血红素氧合酶HugZ是幽门螺旋杆菌(Helicobacter pylori)利用宿主血红素作为铁源的关键蛋白.HugZ的His245残基侧链咪唑基与血红素中心铁配位结合,是酶活中心的重要组成部分.用定点突变的方法构建HugZ突变体H245A、H249A和H245A/H249A基因,并将突变体蛋白表达纯化.通过X射线晶体学途径解析了突变体H245A与血红素复合物的2.55魡分辨率晶体结构.结构解析表明,HugZ的His249残基侧链咪唑基团与血红素的铁原子结合,从而补偿了His245侧链缺失.这种结构特征在已知血红素氧合酶中未曾发现.Val238ψ平面的可翻转和Gly239的柔性是His249能与血红素配位结合的关键原因,二者的共同作用改变了C端肽链的走向,使Val238与His249之间的柔性回折与α1螺旋的相互作用发生解离,并向远离血红素的方向伸展.HugZ蛋白与血红素结合的光谱实验证明HugZ柔性C端上的组氨酸残基有利于HugZ与血红素的结合.研究结果表明,含多个组氨酸残基柔性C端的存在有利于血红素氧合酶HugZ结合和分解血红素.
The heme oxygenase, HugZ, is a key protein of Helicobacter pylori that utilizes host heme as an iron source.HuzZ His245 residue side-chain imidazolyl binds to the heme center iron and is an important component of the enzyme activity center The HugZ mutant H245A, H249A and H245A / H249A genes were constructed by site-directed mutagenesis, and the mutant protein was expressed and purified.It was analyzed by X-ray crystallography that the crystal structure of H245A and heme complex at 2.55 魡 resolution Structure.Analysis of structure shows that the side chain imidazyl group of His249 residue of HugZ binds to the iron atom of heme to compensate for the deletion of His245 side chain.This structural feature was not found in the known heme oxygenase.Val238ψ plane The turnover of Gly239 and flexibility of Gly239 His249 with the heme coordination with the key reasons for the combination of the two changes in the C-terminal peptide chain, Val238 and His249 flexible back between the α1 helix interaction occurs Dissociation and extend away from the heme.HuZZ protein and heme binding spectroscopy experiments show HugZ flexible C-terminal histidine residue is conducive to HugZ and heme binding. The results show, comprising a plurality of histidine residues present in the C-terminus of the flexible facilitate binding of heme oxygenase and decomposition HugZ heme.