Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Via L. Borsari 46, 44121 Ferrara, Italy; Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland.
Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Via L. Borsari 46, 44121 Ferrara, Italy.
J Inorg Biochem. 2021 Jan;214:111304. doi: 10.1016/j.jinorgbio.2020.111304. Epub 2020 Nov 4.
Helicobacter pylori is a gram-negative bacterium with gastric localization that can cause many gastrointestinal disorders. Its survival in the host environment strictly requires an efficient regulation of its metal homeostasis, in particular of Ni(II) ions, crucial for the synthesis of some essential enzymes. Hpn is a protein of 60 amino acids, 47% of which are histidines, expressed by H. pylori and avid for nickel, characterized by the presence of an ATCUN (Amino Terminal Cu(II)- and Ni(II)-binding) motif and by two further histidine residues which can act as additional metal anchoring sites. We decided to deepen the following aspects: (i) understanding the role of each histidine in the coordination of metal ions; (ii) comparing the binding affinities for Cu(II), Ni(II) and Zn(II) ions, which are potentially competing metals in vivo; (iii) understanding the Hpn ability of forming ternary and poly-nuclear complexes. For these purposes, we synthesized the Hpn N-terminal "wild-type" sequence (MAHHEEQHG-Am) and the following peptide analogues: MAAHEEQHG-Am, MAHAEEQHG-Am, MAHHEEQAG-Am and MAHAEEQAG-Am. Our results highlight that the histidines in position 4 and 8 lead to the formation of Cu(II) binuclear complexes. The ATCUN motif is by far the most efficient binding site for Cu(II) and Ni(II), while macrochelate Zn(II) complexes are formed thanks to the presence of several suitable anchoring sites (His and Glu). The metal binding affinities follow the order Zn(II) < Ni(II) < < Cu(II). In solutions containing equimolar amount of wild-type ligand, Cu(II) and Ni(II), the major species above pH 5.5 are hetero-binuclear complexes.
幽门螺杆菌是一种革兰氏阴性细菌，具有胃部定位性，可以引起许多胃肠道疾病。其在宿主环境中的生存严格依赖于其金属内稳态的有效调节，特别是 Ni(II) 离子，这对于一些必需酶的合成至关重要。Hpn 是一种由 60 个氨基酸组成的蛋白质，其中 47%为组氨酸，由幽门螺杆菌表达，对镍具有强烈的亲和力，其特点是存在 ATCUN（氨基末端 Cu(II)-和 Ni(II)-结合）基序和另外两个组氨酸残基，它们可以作为额外的金属锚定位点。我们决定深入研究以下几个方面：（i）了解每个组氨酸在配位金属离子中的作用；（ii）比较 Cu(II)、Ni(II)和 Zn(II)离子的结合亲和力，这些离子在体内是潜在的竞争金属；（iii）了解 Hpn 形成三元和多核配合物的能力。为此，我们合成了 Hpn N 端“野生型”序列（MAHHEEQHG-Am）和以下肽类似物：MAAHEEQHG-Am、MAHAEEQHG-Am、MAHHEEQAG-Am 和 MAHAEEQAG-Am。我们的结果表明，第 4 位和第 8 位的组氨酸导致 Cu(II)双核配合物的形成。到目前为止，ATCUN 基序是 Cu(II)和 Ni(II)的最有效结合位点，而大环螯合 Zn(II)配合物的形成则得益于存在多个合适的锚定位点（His 和 Glu）。金属结合亲和力的顺序为 Zn(II) < Ni(II) < Cu(II)。在含有等摩尔量野生型配体、Cu(II)和 Ni(II)的溶液中，在 pH 值高于 5.5 的情况下，主要物种是杂双核配合物。
