Kim Sella, Lee Ji-Hye, Seok Jong Hyeon, Park Yi-Ho, Jung Sang Won, Cho Art E, Lee Cheolju, Chung Mi Sook, Kim Kyung Hyun
Department of Biotechnology & Bioinformatics, Korea University, Sejong 339-700, Korea.
Functional Proteomics Center, Korea Institute of Science and Technology, Seoul 136-791, Korea.
J Mol Biol. 2016 Dec 4;428(24 Pt B):5007-5018. doi: 10.1016/j.jmb.2016.10.022. Epub 2016 Oct 21.
Iron and oxygen chemistry is mediated by iron proteins for many biological functions. Carboxylate-bridged diiron enzymes including ferritin have the common mechanism of oxygen activation via peroxodiferric intermediates. However, the route for iron uptake and the structural identification of intermediates still remain incomplete. The 4-fold symmetry channel of Helicobacter pylori ferritin was previously proposed as the iron-uptake route in eubacteria, but the amino acid residues at the 4-fold channel are not highly conserved. Here, we show evidence for a short path for iron uptake from His93 on the surface to the ferroxidase center in H. pylori ferritin and Escherichia coli ferritin. The amino acid residues along this path are highly conserved in Gram-negative bacteria and some archaea, and the mutants containing S20A and H93L showed significantly decreased iron oxidation. Surprisingly, the E. coli ferritin S20A crystal structure showed oxygen binding and side-on, symmetric μ-η:η peroxodiferric and oxodiferric intermediates. The results provide the structural basis for understanding the chemical nature of intermediates in iron oxidation in bacteria and some of archaea.
铁与氧的化学反应由铁蛋白介导，以实现多种生物学功能。包括铁蛋白在内的羧酸盐桥连双铁酶具有通过过氧二铁中间体激活氧的共同机制。然而，铁的摄取途径以及中间体的结构鉴定仍不完整。先前有人提出幽门螺杆菌铁蛋白的四重对称通道是真细菌中铁的摄取途径，但四重通道处的氨基酸残基并非高度保守。在此，我们证明了从幽门螺杆菌铁蛋白和大肠杆菌铁蛋白表面的His93到铁氧化酶中心存在一条铁摄取的短路径。这条路径上的氨基酸残基在革兰氏阴性菌和一些古细菌中高度保守，含有S20A和H93L的突变体显示铁氧化显著降低。令人惊讶的是，大肠杆菌铁蛋白S20A晶体结构显示了氧结合以及侧面、对称的μ-η:η过氧二铁和氧代二铁中间体。这些结果为理解细菌和一些古细菌中铁氧化中间体的化学性质提供了结构基础。
