Department of Chemistry and Pharmacy, University of Sassari, Italy.
Faculty of Chemistry, University of Wroclaw, Poland.
J Trace Elem Med Biol. 2017 Dec;44:151-160. doi: 10.1016/j.jtemb.2017.07.006. Epub 2017 Jul 29.
Ni(II) stimulates innate immunity via the direct binding to human Toll Like Receptor 4 (hTLR4), the bacterial lypopolysaccharide receptor. The binding is specific for humans and causes nickel contact allergy. The protein sequence analysis of hTLR4 revealed that the ectodomain, the region supposed to coordinate the metal ions, contains a histidine-rich motif that is not conserved among all organisms. To elucidate the role of each histidine residue on the protein-nickel binding, we examined the formation of Ni(II) complexes with the model peptide NH-FQHSNRKQMSERSVFRSRRNRIYRDISHTHTR-COO, which encompasses the sequence 429-460 of hTLR4. The amino acid sequence of the peptide has been modified by the substitution of some selected lipophilic residues (Leu and Phe) with hydrophilic residues (Arg), aiming at increasing the peptide hydro solubility of the protein fragment. Potentiometric, ultraviolet-visible (UV-vis), nuclear magnetic resonance (NMR) and circular dichroism (CD) measurements demonstrate that the non-conserved histidines in the ectodomain cooperate in metal coordination and consequently enable the activation of the molecular mechanism of nickel hypersensitivity reaction.
镍（II）通过直接与人类 Toll 样受体 4（hTLR4）结合来刺激先天免疫，后者是细菌脂多糖的受体。这种结合对人类具有特异性，导致镍接触过敏。hTLR4 的蛋白序列分析表明，其外域，即被认为协调金属离子的区域，包含一个富含组氨酸的基序，该基序在所有生物体中都没有保守。为了阐明每个组氨酸残基在蛋白-镍结合中的作用，我们研究了模型肽 NH-FQHSNRKQMSERSVFRSRRNRIYRDISHTHTR-COO 与 Ni(II) 形成复合物的情况，该肽涵盖了 hTLR4 的序列 429-460。通过用亲水性残基（Arg）替代一些选定的疏水性残基（Leu 和 Phe）来修饰肽的氨基酸序列，旨在增加蛋白片段的肽水溶解度。电位、紫外-可见（UV-vis）、核磁共振（NMR）和圆二色性（CD）测量表明，外域中的非保守组氨酸在金属配位中协同作用，从而使镍超敏反应的分子机制激活。
