Bilin-dependent regulation of chlorophyll biosynthesis by GUN4
Weiqing Zhang, Robert D. Willows, Rui Deng, Li Zheng, Mengqi Li, Yan Wang, Yunling Guo, Weida Shi, Qiuling Fan, Shelley S. Martin, Nathan C. Rockwell, J. Clark Lagarias, Deqiang Duanmu
Abstract
Significance Enzymes of the chlorophyll biosynthetic pathway, which bind protoporphyrin and Mg-porphyrins, are susceptible to damage by singlet oxygen production in the presence of light and oxygen. These studies show that heme-derived linear tetrapyrroles (bilins) both stimulate and protect the protoporphyrin-binding CHLH subunit of Mg chelatase, the first committed enzyme of the chlorophyll synthesis, from self-sensitized photodamage and turnover via formation of nonphotosensitizing GENOMES UNCOUPLED 4 (GUN4):bilin:porphyrin adducts, which deliver protoporphyrin to CHLH. GUN4:bilin adducts likely evolved to sustain chlorophyll biosynthesis in an oxic world, accounting for retention of bilin synthesis in nearly all oxygenic photosynthetic species on Earth.