X-ray dose-dependent structural changes of the [2Fe-2S] ferredoxin from Chlamydomonas reinhardtii

• Published in: Journal of biochemistry (Tokyo) 2020-06, Vol.167 (6), p.549-555
• Main Authors: Ohnishi, Yusuke, Muraki, Norifumi, Kiyota, Daiki, Okumura, Hideo, Baba, Seiki, Kawano, Yoshiaki, Kumasaka, Takashi, Tanaka, Hideaki, Kurisu, Genji
• Format: Article
• Language: English
• Subjects: Chlamydomonas reinhardtii - metabolism; Crystallization; Crystallography, X-Ray; Ferredoxins - chemistry; Ferredoxins - metabolism; Ferredoxins - radiation effects; Models, Molecular; Oxidation-Reduction; Protein Conformation; Recombinant Proteins - chemistry; Recombinant Proteins - metabolism; Recombinant Proteins - radiation effects; X-Ray Absorption Spectroscopy; X-Rays
• ISSN: 0021-924X; 1756-2651
• DOI: 10.1093/jb/mvaa045

Abstract Plant-type ferredoxin (Fd) is an electron transfer protein in chloroplast. Redox-dependent structural change of Fd controls its association with and dissociation from Fd-dependent enzymes. Among many X-ray structures of oxidized Fd have been reported so far, very likely a given number of them was partially reduced by strong X-ray. To understand the precise structural change between reduced and oxidized Fd, it is important to know whether the crystals of oxidized Fd may or may not be reduced during the X-ray experiment. We prepared the thin plate-shaped Fd crystals from Chlamydomonas reinhardtii and monitored its absorption spectra during experiment. Absorption spectra of oxidized Fd crystals were clearly changed to that of reduced form in an X-ray dose-dependent manner. In another independent experiment, the X-ray diffraction images obtained from different parts of one single crystal were sorted and merged to form two datasets with low and high X-ray doses. An Fo–Fo map calculated from the two datasets showed that X-ray reduction causes a small displacement of the iron atoms in the [2Fe-2S] cluster. Both our spectroscopic and crystallographic studies confirm X-ray dose-dependent reduction of Fd, and suggest a structural basis for its initial reduction step especially in the core of the cluster.