Identification of cysteine residues involved in thioredoxin-dependent redox regulation of CHLI1, a subunit of Mg-chelatase in Arabidopsis thaliana

Abstract

Mg-chelatase catalyzes the insertion of Mg²⁺ into protoporphyrin IX and is composed of three subunits, CHLI, CHLD and CHLH. Mg-insertion by Mg-chelatase requires ATP hydrolysis attributed by CHLI, which primary determines the rate of Mg-insertion. Determination of three-dimensional structure of Rhodobacter BCHI revealed that the protein is a member of AAA⁺-protein family. Our previous study showed that CHLI1 of Arabidopsis is a target protein of chloroplast thioredoxin. In this study, we identified one critical disulfide bond involved in the redox regulation of ATPase activity based on the analysis of point mutation of 4 cysteine residues of CHLI1. These cysteines are expected to be located in close proximity within the C-terminal regulatory domain based on the BCHLI structure. Thus, the identified one crucial disulfide bond located in the C-terminal domain of CHLI1 may be involved in thioredoxin-dependent redox regulation, which may regulate the ATPase activity of CHLI1.