Light- and Metabolism-related Regulation of the Chloroplast ATP Synthase Has Distinct Mechanisms and Functions

• Published in: The Journal of biological chemistry Vol. 288; no. 18; pp. 13156 - 13163
• Main Authors: Kohzuma, Kaori, Dal Bosco, Cristina, Meurer, Jörg, Kramer, David M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 03.05.2013; American Society for Biochemistry and Molecular Biology
• Subjects: Allosteric Regulation - physiology; Amino Acid Substitution; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; ATP Synthase; Carbon Dioxide - metabolism; Chloroplast; Chloroplast Proton-Translocating ATPases - genetics; Chloroplast Proton-Translocating ATPases - metabolism; Light; Mutation, Missense; Oxidation-Reduction; Photoperiod; Photosynthesis; Plant Biology; Proton Transport; Redox Regulation; Thioredoxin; Thylakoids - enzymology; Thylakoids - genetics; ATP Synthase; Redox Regulation; Photosynthesis; Thioredoxin; Proton Transport; Chloroplast
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M113.453225

The chloroplast CF0-CF1-ATP synthase (ATP synthase) is activated in the light and inactivated in the dark by thioredoxin-mediated redox modulation of a disulfide bridge on its γ subunit. The activity of the ATP synthase is also fine-tuned during steady-state photosynthesis in response to metabolic changes, e.g. altering CO2 levels to adjust the thylakoid proton gradient and thus the regulation of light harvesting and electron transfer. The mechanism of this fine-tuning is unknown. We test here the possibility that it also involves redox modulation. We found that modifying the Arabidopsis thaliana γ subunit by mutating three highly conserved acidic amino acids, D211V, E212L, and E226L, resulted in a mutant, termed mothra, in which ATP synthase which lacked light-dark regulation had relatively small effects on maximal activity in vivo. In situ equilibrium redox titrations and thiol redox-sensitive labeling studies showed that the γ subunit disulfide/sulfhydryl couple in the modified ATP synthase has a more reducing redox potential and thus remains predominantly oxidized under physiological conditions, implying that the highly conserved acidic residues in the γ subunit influence thiol redox potential. In contrast to its altered light-dark regulation, mothra retained wild-type fine-tuning of ATP synthase activity in response to changes in ambient CO2 concentrations, indicating that the light-dark- and metabolic-related regulation occur through different mechanisms, possibly via small molecule allosteric effectors or covalent modification. Background: Chloroplast ATP synthase activity is regulated by both light and metabolic factors, but the relationship between these regulatory modes is not established. Results: Mutating three highly conserved acidic amino acid residues in the γ subunit alters light- but not metabolism-induced regulation. Conclusion: Metabolism and light regulation operates via distinct mechanisms. Significance: The chloroplast ATP synthase is a key control point for the light and dark reactions of photosynthesis.