報告題目：Electron Transfer Regulation in Tetraheme Cytochromes Revealed by NMR
報告人:    Prof. Hideo Akutsu
     Osaka University
    Yokohama City University
地    點：beat365化學學院A717學術報告廳
時    間：2019年05月13日(星期一) 上午10:00
主請人：劉忠範 院士

報告摘要：

Cytochromes are ubiquitous heme-proteins that are involved in a wide variety of redox reactions in biological electron transport systems. Some cytochromes have multiple hemes, generally protoporphyrins coordinated to iron. They are mainly found in bacteria that can be traced back more than 500 million years to the anaerobic world, and reveal special redox features because of heme-heme interactions. Such features will be discussed in this talk focusing on c-type tetraheme-cytochromes [1, 2]. A cyclic heme architecture and its environment including bis-imidazole coordination and heme exposure realize extremely low redox potentials of cytochrome c₃. To elucidate its mechanism, the effect of extensive mutations at conserved and non-conserved aromatic residues on the coordination property of heme irons was investigated, using NMR and X-ray crystallography [2]. The results suggested the importance of p-p interaction and p-cation interactions among hemes and conserved aromatic rings. On determination of heme reduction potentials, each heme in cytochrome c₃ was expected to play a different role in the electron transport with other redox proteins. It was supported by the interaction with [NiFe] hydrogenase. Design of the heme architecture is also important. In contrast to cytochrome c₃, the chain-like heme architecture in Shewanella small tetraheme cytochrome c provides a pathway for directional electron transfer. Actually, soluble fumarate reductase visualizes a directional electron transfer through a molecular wire. Thus, the tetraheme architectures can work as sophisticated devices.

References:

1) H. Akutsu and Y. Takayama, Functional roles of heme architecture and its environment in tetraheme cytochrome c, Accounts Chem. Res., 40, 171-178 (2007).  

2) Y. Takayama, M. Taketa-Sato, H. Komori, K. Morita, S.-J. Kang, Y. Higuchi, and H. Akutsu, Role of p-electron systems in stabilization of the oxidized tetraheme architecture in cytochrome c₃, Bull. Chem. Soc. Jpn., 84, 1096-1101 (2011).