Abstract
Photosynthetic efficiency depends on equal light energy conversion by two spectrally distinct, serially-connected photosystems. The redox state of the plastoquinone pool, located between the two photosystems, is a key regulatory signal that initiates acclimatory changes in the relative abundance of photosystems. The Chloroplast Sensor Kinase (CSK) links the plastoquinone redox signal with photosystem gene expression but the mechanism by which it monitors the plastoquinone redox state is unclear. Here we show that the purified Arabidopsis and Phaeodactylum CSK and the cyanobacterial CSK homologue, Histidine kinase 2 (Hik2), are iron-sulfur proteins. The Fe-S cluster of CSK is further revealed to be a high potential redox-responsive [3Fe-4S] center. CSK responds to redox agents with reduced plastoquinone suppressing its autokinase activity. Redox changes within the CSK iron-sulfur cluster translate into conformational changes in the protein fold. These results provide key insights into redox signal perception and propagation by the CSK-based chloroplast two-component system.
Highlights
Photosynthetic efficiency depends on equal light energy conversion by two spectrally distinct, serially-connected photosystems
We further show that the redox changes in the Fe-S cluster induce conformational changes in the Chloroplast Sensor Kinase (CSK) protein and modulate its autokinase activity
We further examined the presence of an Fe-S cluster in CSK by electron paramagnetic resonance (EPR) spectroscopy
Summary
Photosynthetic efficiency depends on equal light energy conversion by two spectrally distinct, serially-connected photosystems. The Chloroplast Sensor Kinase (CSK) links the plastoquinone redox signal with photosystem gene expression but the mechanism by which it monitors the plastoquinone redox state is unclear. Redox changes within the CSK iron-sulfur cluster translate into conformational changes in the protein fold These results provide key insights into redox signal perception and propagation by the CSK-based chloroplast two-component system. In changing conditions of light quality, the redox state of the interphotosystem electron carrier plastoquinone (PQ) is a key regulatory signal that governs the expression of genes encoding core protein subunits of the photosystems[7]. CSK and its cyanobacterial homolog, Histidine kinase 2 (Hik2), provide the crucial signal transduction chain that links PQ with photosystem gene expression[9,11]. We further show that the redox changes in the Fe-S cluster induce conformational changes in the CSK protein and modulate its autokinase activity
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