Degradation of Rubisco SSU during oxidative stress triggers aggregation of Rubisco particles in <Emphasis Type="Italic">Chlamydomonas reinhardtii</Emphasis> |
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Authors: | Joel?A?Knopf Email author" target="_blank">Michal?ShapiraEmail author |
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Institution: | (1) Department of Life-Sciences, The Ben-Gurion University of the Negev, PO Box 653, Beer Sheva, 84105, Israel |
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Abstract: | Oxidative stress in plants and green algae has multiple damaging effects, and leads to the degradation of Ribulose-1,5-biphosphate
carboxylase/oxygenase (Rubisco). We recently showed for the green algae Chlamydomonas reinhardtii that in response to a photo-oxidative stress, nascent synthesis of its chloroplast encoded large subunit (LSU) stops. In
parallel, newly synthesized small subunits (SSU) that are encoded by the nucleus are rapidly degraded, thus assembly of new
holoenzyme particles is inhibited. Here we show that under extreme oxidizing conditions, the steady-state level of the SSU
is also reduced. Cleavage of the LSU under oxidizing conditions is well established, and we show, using sucrose gradients,
that the resulting fragments of the LSU co-exist as parts of the holoenzyme. In parallel, we demonstrate the selective in-vivo
formation of high-density aggregates of Rubisco particles, in response to oxidative stress. Given the known tendency of unassembled
LSUs to aggregate, we propose that the rapid elimination of the SSU during oxidative stress along with the fragmentation of
the LSU and formation of intra-protein disulfide bridges, leads to the observed aggregation of Rubisco particles. Indeed,
we note here a substantially decreased ratio of SSU in the aggregated Rubisco particles. We also observed that this aggregation
marks the viability threshold of C. reinhardtii cells exposed to oxidative stress. |
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Keywords: | Rubisco Aggregation Chlamydomonas reinhardtii Photo-oxidative stress |
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