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Metal-binding properties of an Hpn-like histidine-rich protein

机译：Hpn样组氨酸富集蛋白的金属结合特性

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The Hpn-like protein (Hpnl), a histidine- and glutamine-rich protein, is critical for Helicobacter pylori colonization in human gastric muscosa. In this study, the thermodynamic properties of Ni~(II), Cu~(II), Co ~(II), and Zn~(II) toward Hpnl were studied by isothermal titration calorimetry (ITC). We found that Hpnl exhibits two independent binding sites for Ni~(II) as opposed to one site for Cu~(II), Co ~(II), and Zn~(II). Protease digestion and chemical denaturation analysis further revealed that Ni~(II) confers a higher stability upon Hpnl than other divalent metal ions. The potential NiII binding sites are localized in the His-rich domain of Hpnl as confirmed by mutagenesis in combination with modification of histidine residues of the protein. We also demonstrated that the single mutants (H29A and H31A) and tetrameric mutant (H29-32A) cut nearly half of the binding capacity of Hpnl towards nickel ions, whereas other histidine residues (His30, 32, 38, 39, 40, and 41) are nonessential for nickel coordination. Escherichia coli cells that harbored H29A, H31A, and H29-32A mutant genes exhibited less tolerance toward high concentrations of extracellular nickel ions than those with the wild-type gene. Our combined data indicated that the conserved histidine residues, His29 and His31 in the His-rich domain of Hpnl, are critical for nickel binding, and such a binding is important for Hpnl protein to fulfill its biological functions.
机译：Hpn样蛋白（Hpnl）是富含组氨酸和谷氨酰胺的蛋白，对于幽门螺杆菌在人胃黏膜中的定殖至关重要。通过等温滴定热法（ITC）研究了Ni〜（II），Cu〜（II），Co〜（II）和Zn〜（II）对Hpnl的热力学性质。我们发现，Hpnl对Ni〜（II）表现出两个独立的结合位点，而对Cu〜（II），Co〜（II）和Zn〜（II）则表现出一个独立的结合位点。蛋白酶消化和化学变性分析进一步表明，Ni〜（II）对Hpnl具有比其他二价金属离子更高的稳定性。如通过诱变结合蛋白质的组氨酸残基的修饰所证实的，潜在的NiII结合位点位于Hpn1的富含His的结构域中。我们还证明了单个突变体（H29A和H31A）和四聚体突变体（H29-32A）削减了Hpnl对镍离子的结合能力的近一半，而其他组氨酸残基（His30、32、38、39、40和41 ）对于镍的配位是不必要的。与野生型基因相比，具有H29A，H31A和H29-32A突变基因的大肠杆菌细胞对高浓度细胞外镍离子的耐受性较低。我们的综合数据表明，Hpnl富含His的结构域中的保守组氨酸残基His29和His31对于镍结合至关重要，而这种结合对于Hpnl蛋白实现其生物学功能很重要。

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