Bilin-dependent regulation of chlorophyll biosynthesis by GUN4

Biosyntheses of chlorophyll and heme in oxygenic phototrophs share a common trunk pathway that diverges with insertion of magnesium or iron into the last common intermediate, protoporphyrin IX. Since both tetrapyrroles are pro-oxidants, it is essential that their metabolism is tightly regulated. Her...

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Veröffentlicht in:Proceedings of the National Academy of Sciences - PNAS 2021-05, Vol.118 (20), p.1-9
Hauptverfasser: Zhang, Weiqing, Willows, Robert D., Deng, Rui, Li, Zheng, Li, Mengqi, Wang, Yan, Guo, Yunling, Shi, Weida, Fan, Qiuling, Martin, Shelley S., Rockwell, Nathan C., Lagarias, J. Clark, Duanmu, Deqiang
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Sprache:eng
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Zusammenfassung:Biosyntheses of chlorophyll and heme in oxygenic phototrophs share a common trunk pathway that diverges with insertion of magnesium or iron into the last common intermediate, protoporphyrin IX. Since both tetrapyrroles are pro-oxidants, it is essential that their metabolism is tightly regulated. Here, we establish that heme-derived linear tetrapyrroles (bilins) function to stimulate the enzymatic activity of magnesium chelatase (MgCh) via their interaction with GENOMES UNCOUPLED 4 (GUN4) in the model green alga Chlamydomonas reinhardtii. A key tetrapyrrole-binding component of MgCh found in all oxygenic photosynthetic species, CrGUN4, also stabilizes the bilin-dependent accumulation of protoporphyrin IX-binding CrCHLH1 subunit of MgCh in light-grown C. reinhardtii cells by preventing its photooxidative inactivation. Exogenous application of biliverdin IXα reverses the loss of CrCHLH1 in the bilin-deficient heme oxygenase (hmox1) mutant, but not in the gun4 mutant. We propose that these dual regulatory roles of GUN4: bilin complexes are responsible for the retention of bilin biosynthesis in all photosynthetic eukaryotes, which sustains chlorophyll biosynthesis in an illuminated oxic environment.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.2104443118