Yamamoto Yasuhiko, Araki Haruka, Shinomiya Ryosuke, Hayasaka Kosuke, Nakayama Yusaku, Ochi Kentaro, Shibata Tomokazu, Momotake Atsuya, Ohyama Takako, Hagihara Masaki, Hemmi Hikaru
Department of Chemistry , University of Tsukuba , Tsukuba 305-8571 , Japan.
Tsukuba Research Center for Energy Materials Science (TREMS) , University of Tsukuba , Tsukuba 305-8571 , Japan.
Biochemistry. 2018 Oct 16;57(41):5938-5948. doi: 10.1021/acs.biochem.8b00792. Epub 2018 Oct 4.
Heme in its ferrous and ferric states [heme(Fe) and heme(Fe), respectively] binds selectively to the 3'-terminal G-quartet of all parallel-stranded monomeric G-quadruplex DNAs formed from inosine(I)-containing sequences, i.e., d(TAGGGTGGGTTGGGTGIG) DNA(18mer) and d(TAGGGTGGGTTGGGTGIGA) DNA(18mer/A), through a π-π stacking interaction between the porphyrin moiety of the heme and the G-quartet, to form 1:1 complexes [heme-DNA(18mer) and heme-DNA(18mer/A) complexes, respectively]. These complexes exhibited enhanced peroxidase activities, compared with that of heme(Fe) alone, and the activity of the heme(Fe)-DNA(18mer/A) complex was greater than that of the heme(Fe)-DNA(18mer) one, indicating that the 3'-terminal A of the DNA sequence acts as an acid-base catalyst that promotes the catalytic reaction. In the complexes, a water molecule (HO) at the interface between the heme and G-quartet is coordinated to the heme Fe atom as an axial ligand and possibly acts as an electron-donating ligand that promotes heterolytic peroxide bond cleavage of hydrogen peroxide bound to the heme Fe atom, trans to the HO, for the generation of an active species. The intermolecular nuclear Overhauser effects observed among heme, DNA, and Fe-bound HO indicated that the HO rotates about the HO-Fe coordination bond with respect to both the heme and DNA in the complex. Thus, the HO in the complex is unique in terms of not only its electronic properties but also its dynamic ones. These findings provide novel insights into the design of heme-deoxyribozymes and -ribozymes.
亚铁态和铁态的血红素[分别为血红素(Fe²⁺)和血红素(Fe³⁺)]通过血红素的卟啉部分与鸟嘌呤四重体之间的π-π堆积相互作用，选择性地结合到由含次黄嘌呤核苷(I)的序列形成的所有平行链单体G-四链体DNA的3'-末端鸟嘌呤四重体上，即d(TAGGGTGGGTTGGGTGIG) DNA(18聚体)和d(TAGGGTGGGTTGGGTGIGA) DNA(18聚体/A)，形成1:1复合物[分别为血红素-DNA(18聚体)和血红素-DNA(18聚体/A)复合物]。与单独的血红素(Fe²⁺)相比，这些复合物表现出增强的过氧化物酶活性，并且血红素(Fe²⁺)-DNA(18聚体/A)复合物的活性大于血红素(Fe²⁺)-DNA(18聚体)复合物的活性，这表明DNA序列的3'-末端A作为酸碱催化剂促进催化反应。在复合物中，血红素与鸟嘌呤四重体之间界面处的水分子(H₂O)作为轴向配体与血红素铁原子配位，并可能作为供电子配体促进与血红素铁原子结合的过氧化氢的异裂过氧化物键断裂，该过氧化氢与H₂O处于反位，以产生活性物种。在血红素、DNA和与铁结合的H₂O之间观察到的分子间核Overhauser效应表明，在复合物中，H₂O围绕H₂O-铁配位键相对于血红素和DNA旋转。因此，复合物中的H₂O不仅在其电子性质方面而且在其动力学性质方面都是独特的。这些发现为血红素脱氧核酶和核酶的设计提供了新的见解。
