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

Hochmal A, Zinzius K, Charoenwattanasatien R, Gäbelein P, Mutoh R, Tanaka H, Schulze S, Liu G, Scholz M, Nordhues A, Offenborn J, Petroutsos D, Finazzi G, Fufezan C, Huang K, Kurisu G, Hippler M

Nature communications
2016 vol: 7 (May) pp: 11847

Abstract

Calcium (Ca2+) 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 Ca2+- and redox-related signalling. This protein, designated as calredoxin (CRX), combines four Ca2+-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 Ca2+-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). Ca2+-binding to CRX is critical for its TRX activity and for efficient binding and reduction of PRX1. Thereby, CRX represents a new class of Ca2+-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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