The Allosteric Role of the AAA+ Domain of ChlD Protein from the Magnesium Chelatase of Synechocystis Species PCC 6803

Magnesium chelatase catalyzes the first essential step in chlorophyll biosynthesis. Results: Mutations in the AAA+ domain of the magnesium chelatase ChlD subunit reduce but do not abolish catalytic activity. Conclusion: ChlD is an allosteric regulator of magnesium chelatase. Significance: These observations reveal an essential role for the ChlD protein in the first committed stage in chlorophyll biosynthesis. Magnesium chelatase is an AAA+ ATPase that catalyzes the first step in chlorophyll biosynthesis, the energetically unfavorable insertion of a magnesium ion into a porphyrin ring. This enzyme contains two AAA+ domains, one active in the ChlI protein and one inactive in the ChlD protein. Using a series of mutants in the AAA+ domain of ChlD, we show that this site is essential for magnesium chelation and allosterically regulates Mg2+ and MgATP2− binding.