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bioRxiv · 10.1101/2024.11.21.624570

Switchable client specificity in a dual functional chaperone coordinates light harvesting complex biogenesis

Siegel, A. R.·Kroon, G.·Wright, P. E.·Shan, S.-o.
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Abstract

The proper assembly of light harvesting complexes (LHCs) is critical for photosynthesis and requires the biogenesis of light-harvesting chlorophyll a,b-binding proteins (LHCPs) to be coordinated with the biosynthesis of chlorophylls (Chl). The mechanism underlying this coordination is not well understood. Here we show that a conserved molecular chaperone in chloroplasts, cpSRP43, provides a molecular thermostat that helps maintain this coordination. cpSRP43 undergoes a conformational rearrangement between a well-folded closed state and a partially disordered open state. Closed cpSRP43 is dedicated to the de novo biogenesis of LHCPs, whereas open cpSRP43 protects multiple Chl biosynthesis enzymes from heat-induced destabilization. Rising temperature shifts cpSRP43 to the open state and thus enables it to protect Chl biosynthesis enzymes that are heat-destabilized. Our results reveal the molecular basis of a post-translational mechanism for the thermo-adaptation of LHC biogenesis. They also demonstrate how an ATP-independent chaperone uses conformational dynamics to switch its activity and client selectivity, thereby adapting to different proteostatic demands under shifting environmental conditions. TeaserA thermo-switchable molecular chaperone helps coordinate light harvesting complex assembly during photosynthesis.

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Siegel, A. R., Kroon, G., Wright, P. E., Shan, S.-o.. 2024-11-21. Switchable client specificity in a dual functional chaperone coordinates light harvesting complex biogenesis. https://doi.org/10.1101/2024.11.21.624570

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