Calredoxin represents a novel type of calcium-dependent sensor-responder connected to redox regulation in the chloroplast

Ana Karina Hochmal, Karen Zinzius, Ratana Charoenwattanasatien, Philipp Gäbelein, Risa Mutoh, Hideaki Tanaka, Stefan Schulze, Gai Liu, Martin Scholz, André Nordhues, Jan Niklas Offenborn, Dimitris Petroutsos, Giovanni Finazzi, Christian Fufezan, Kaiyao Huang, Genji Kurisu & Michael Hippler

Nature Communications
2016 vol: 7 pp: 11847 doi: 10.1038/ncomms11847

Abstract
Calcium (Ca(2+)) and redox signalling play important roles in acclimation processes from archaea to eukaryotic organisms. Herein we characterized a unique protein from Chlamydomonas reinhardtii that has the competence to integrate Ca(2+)- and redox-related signalling. This protein, designated as calredoxin (CRX), combines four Ca(2+)-binding EF-hands and a thioredoxin (TRX) domain. A crystal structure of CRX, at 1.6 Å resolution, revealed an unusual calmodulin-fold of the Ca(2+)-binding EF-hands, which is functionally linked via an inter-domain communication path with the enzymatically active TRX domain. CRX is chloroplast-localized and interacted with a chloroplast 2-Cys peroxiredoxin (PRX1). Ca(2+)-binding to CRX is critical for its TRX activity and for efficient binding and reduction of PRX1. Thereby, CRX represents a new class of Ca(2+)-dependent ‘sensor-responder’ proteins. Genetically engineered Chlamydomonas strains with strongly diminished amounts of CRX revealed altered photosynthetic electron transfer and were affected in oxidative stress response underpinning a function of CRX in stress acclimation.

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Topics: Intracellular signalling peptides and proteins, Plant signalling, Stress signalling, Monolith – MicroScale Thermophoresis, MST, Proteins, Publications