The chloroplast ATP synthase redox domain in Chlamydomonas reinhardtii eludes activity regulation for heterotrophic dark metabolism

• 成果类型: Article
• 署名作者: Lebok, Lando; Buchert, Felix
• 署名单位: University of Munster
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-12044
• DOI: 10.1073/pnas.2412589121
• 发表日期: 2024-11-12
• 关键词: photosynthetic electron-transport; plastid terminal oxidase; thioredoxin reductase c; potential difference; cysteine bridge; epsilon-subunit; photophosphorylation; modulation; activation; gradient

摘要

To maintain CO2 fixation in the Calvin-Benson-Bassham cycle, multistep regulation of the chloroplast ATP synthase (CF1Fo) is crucial to balance the ATP output of photosynthesis with protection of the apparatus. A well-studied mechanism is thiol modulation; a light/dark regulation through reversible cleavage of a disulfide in the CF1Fo gamma-subunit. The disulfide hampers ATP synthesis and hydrolysis reactions in dark-adapted CF1Fo from land plants by increasing the required transmembrane electrochemical proton gradient (Delta(mu) over tilde (H+)). Here, we show in Chlamydomonas reinhardtii that algal CF1Fo is differently regulated in vivo. A specific hairpin structure in the gamma-subunit redox domain disconnects activity regulation from disulfide formation in the dark. Electrochromic shift measurements suggested that the hairpin kept wild-type CF1Fo active, whereas the enzyme was switched off in algal mutant cells expressing a plant-like hairpin structure. The hairpin segment swap resulted in an elevated Delta(mu) over tilde (H+) threshold to activate plant-like CF1Fo, increased by similar to 1.4 photosystem (PS) I charge separations. The resulting dark-equilibrated Delta(mu) over tilde (H+) dropped in the mutants by similar to 2.7 PSI charge separation equivalents. Photobioreactor experiments showed no phenotypes in autotrophic aerated mutant cultures. In contrast, chlorophyll fluorescence measurements under heterotrophic dark conditions point to an altered dark metabolism in cells with the plant-like CF1Fo as the result of bioenergetic deviations from wild-type. Our results suggest that the lifestyle of C. reinhardtii requires a specific CF1Fo dark regulation that partakes in metabolic coupling between the chloroplast and acetate-fueled mitochondria.