Calcium-dependent regulation of photosynthesis in Chlamydomonas reinhardtii: Structural and functional dynamics of calredoxin, a chloroplast Ca2+-dependent thioredoxin
Final Report Abstract
Chloroplast Ca2+-transport (import/export), allocation, sensing and/or signaling appear to be essential for chloroplast biology and in particular for effective photosynthesis in green algae and vascular plants. There is evidence that a regulatory network exists which senses the chloroplast Ca2+ content, participates in regulation of photosynthesis and control of protein expression. Yet, basic aspects of this network are unknown. Herein, we focused on calredoxin (CRX), a newly identified factor in this network, which operates as a Ca2+-dependent thioredoxin (TRX) in the chloroplast. As a Ca2+-dependent sensor-responder, CRX links calcium and redox responses. Ca2+-binding to CRX remodels its structure allowing binding and electron transfer to chloroplast peroxiredoxin (PRX1), important for photo-acclimation responses. In our work we provided mechanistic insights into the protein-protein interaction between CRX and PRX1. Our structural data revealed that Ca2+-driven structural changes, namely the elongation of the CRX structure upon Ca2+-binding, permit binding and electron transfer between CRX and PRX1. We further dissected the interconnection of CRX in the Ca2+- and redox-dependent regulatory networks via quantitative proteomics. To this end, we took advantage of the crx insertional mutant (IMcrx), two CRISPR-Cas9-generated knockout mutants (crx KOs, E1 and A5) and two rescued strains (IM-R and A5R). The data revealed coregulation of CRX and a chloroplast NADPH-dependent thioredoxin reductase (NTRC). Further, enzymatic assays revealed that CRX inhibits NADPH-dependent reduction of oxidized chloroplast PRX1 via NTRC and discovered that the function of the NADPH-NTRC complex is under strict control of CRX. Notably, the absence of CRX under HL conditions severely inhibited light-driven CO2 fixation, underpinning the importance of CRX for redox tuning as well as for efficient photosynthesis. These insights expand the link between photoprotection and photosynthesis as well as between calcium and redox control in chloroplasts.
Publications
- (2018) X-ray crystallographic and high-speed AFM studies of peroxiredoxin 1 from Chlamydomonas reinhardtii. Acta Crystallogr F Struct Biol Commun 74: 86-91
Charoenwattanasatien R, Tanaka H, Zinzius K, Hochmal AK, Mutoh R, Yamamoto D, Hippler M, Kurisu G
(See online at https://doi.org/10.1107/s2053230x17018507) - (2020) Calcium sensing via EF-hand 4 enables thioredoxin activity in the sensor-responder protein calredoxin in the green alga Chlamydomonas reinhardtii. J Biol Chem 295: 170-180
Charoenwattanasatien R, Zinzius K, Scholz M, Wicke S, Tanaka H, Brandenburg JS, Marchetti GM, Ikegami T, Matsumoto T, Oda T, Sata M, Hippler M, Kurisu G
(See online at https://doi.org/10.1074/jbc.ra119.008735) - (2022) Calredoxin regulates the chloroplast NADPH-dependent thioredoxin reductase in Chlamydomonas reinhardtii. BioRxiv
Zinzius K, Marchetti GM, Fischer R, Milrad Y, Oltmanns A, Kelterborn S, Yacoby I, Hegemann P, Scholz M, Hippler M
(See online at https://doi.org/10.1101/2022.11.22.517551) - (2022) Structural analysis revealed a novel conformation of the NTRC reductase domain from Chlamydomonas reinhardtii. J Struct Biol 214: 107829
Marchetti GM, Fusser F, Singh RK, Brummel M, Koch O, Kummel D, Hippler M
(See online at https://doi.org/10.1016/j.jsb.2021.107829)
