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bioRxiv · 10.1101/2020.07.31.226407

A copper activated protease regulates photosynthetic soluble electron carriers in cyanobacteria

Garcia-Canas, R. M.·Giner-Lamia, J.·Florencio, F. J.·Lopez-Maury, L.
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Abstract

After the Great Oxidation Event (GOE), iron availability was greatly decreased and photosynthetic organisms evolved several alternative proteins and mechanisms. One of these proteins, plastocyanin, is a type I blue-copper protein that can replace cytochrome c6 as a soluble electron carrier between cytochrome b6f and photosystem I. In most cyanobacteria, expression of these two alternative proteins is regulated by copper availability, but the regulatory system remains unknown. Herein, we provide evidence that the regulatory system is composed of a BlaI/CopY family transcription factor (PetR) and a BlaR membrane protease (PetP). PetR represses petE (plastocyanin) expression and activates petJ (cytochrome c6), while PetP controls PetR levels in vivo. Using whole-cell extracts, we demonstrated that PetR degradation requires both PetP and copper. Transcriptomic analysis revealed that the PetRP system regulates only four genes (petE, petJ, slr0601, and slr0602), highlighting its specificity. Furthermore, the presence of petE and petRP in early branching cyanobacteria indicates that acquisition of these genes could represent an early adaptation to decreased iron bioavailability following the GOE. Significance StatementAfter the appearance of oxygenic photosynthesis, Fe became oxidized and its solubility and availability were greatly decreased. This generated a problem for most organisms since they are strongly dependent on Fe, especially photosynthetic organisms. In response, organisms evolved alternatives to Fe-containing proteins such as plastocyanin, a copper protein that substitutes for cytochrome c6 in photosynthesis. Expression of these two proteins in cyanobacteria is regulated by Cu availability, but the regulatory system remains unknown. Herein, we describe the regulatory system for these alternative proteins in photosynthesis in cyanobacteria. The mechanism involves a transcription factor (PetR) and a membrane protease (PetP) that degrades PetR in the presence of Cu.

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Garcia-Canas, R. M., Giner-Lamia, J., Florencio, F. J., Lopez-Maury, L.. 2020-07-31. A copper activated protease regulates photosynthetic soluble electron carriers in cyanobacteria. https://doi.org/10.1101/2020.07.31.226407

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