title: Crystal structure of the catalytic subunit of magnesium chelatase.
abstract: Tetrapyrroles, including haem and chlorophyll, play vital roles for various biological processes, such as respiration and photosynthesis, and their biosynthesis is critical for virtually all organisms. In photosynthetic organisms, magnesium chelatase (MgCh) catalyses insertion of magnesium into the centre of protoporphyrin IX, the branch-point precursor for both haem and chlorophyll, leading tetrapyrrole biosynthesis into the magnesium branch(1,2). This reaction needs a cooperated action of the three subunits of MgCh: the catalytic subunit ChlH and two AAA(+) subunits, ChlI and ChlD (refs 3-5). To date, the mechanism of MgCh awaits further elucidation due to a lack of high-resolution structures, especially for the ∼150 kDa catalytic subunit. Here we report the crystal structure of ChlH from the photosynthetic cyanobacterium Synechocystis PCC 6803, solved at 2.5 Å resolution. The active site is buried deeply inside the protein interior, and the surrounding residues are conserved throughout evolution. This structure helps to explain the loss of function reported for the cch and gun5 mutations of the ChlH subunit, and to provide the molecular basis of substrate channelling during the magnesium-chelating process. The structure advances our understanding of the holoenzyme of MgCh, a metal chelating enzyme other than ferrochelatase.
authors.affiliation: Photosynthesis Research Centre, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.|University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Xuemin
authors.initials: X
authors.lastname: Chen
authors.affiliation: Photosynthesis Research Centre, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.|University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Hua
authors.initials: H
authors.lastname: Pu
authors.affiliation: Photosynthesis Research Centre, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.|University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Fang
authors.affiliation: Photosynthesis Research Centre, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.|University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Xiao
authors.initials: X
authors.lastname: Wang
authors.affiliation: Photosynthesis Research Centre, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.|University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Shun
authors.initials: S
authors.lastname: Zhao
authors.affiliation: Laboratory of Non-coding RNA, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Yajing
authors.initials: Y
authors.lastname: Lin
authors.affiliation: School of Life Sciences, Anhui University, Hefei, Anhui 230601, China.
authors.forename: Min
authors.initials: M
authors.lastname: Zhang
authors.affiliation: Photosynthesis Research Centre, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
authors.forename: Huai-En
authors.initials: HE
authors.lastname: Dai
authors.affiliation: Laboratory of Non-coding RNA, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China.|Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230027, China.
authors.forename: Weimin
authors.initials: W
authors.lastname: Gong
authors.affiliation: Photosynthesis Research Centre, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Liu