Bilin-dependent regulation of chlorophyll biosynthesis by GUN4
- 11 May 2021
- journal article
- research article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences of the United States of America
- Vol. 118 (20)
- https://doi.org/10.1073/pnas.2104443118
Abstract
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.Keywords
Funding Information
- HHS | NIH | National Institute of General Medical Sciences (R01 GM068552)
- U.S. Department of Energy (DOE DE-FG02-09ER16117)
- National Natural Science Foundation of China (31570233)
- National Natural Science Foundation of China (32070268)
- HHS | NIH | National Institute of General Medical Sciences (R35 GM139598)
- Macquarie University (Visiting Research Fellowship)
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