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Storage of energy-rich molecules

Discovery of a giant protein playing a key role in the storage of energy-rich molecules in microalgae

Published on 4 December 2020

DTH1_4.jpgResearchers have just discovered the essential role of a new giant protein (DTH1) involved in the degradation of "lipid droplets", the main site of carbon and energy storage in microalgae. This discovery significantly changes our understanding of their production and storage system for energy-rich molecules. It opens up new perspectives in the development of third-generation biofuels1.

Present on earth for millions of years in all wetlands, microalgae interest scientists for their great environmental adaptation capacities. Indeed, they have been able to colonize both salt and fresh water, from the brackish ones to glaciers or simple soil moisture. In order to cope with very hostile living conditions, some of them have managed to specialize in the storage of reserves of highly energetic molecules by developing specific mechanisms, the mysteries of which scientists are now trying to unravel. Understanding their production systems for "high added value molecules" is crucial for the development of 3rd generation biofuel production. One of the research teams at the Bioscience and biotechnology Institute of Aix-Marseille (BIAM), in collaboration with a Korean team, is working on this subject.

These energy reserves, better known as lipid droplets (LDs), are the essential site of carbon storage in the microalga Chlamydomonas reinhardtii, a model studied in the development of 3rd generation biofuels. These droplets are formed in large numbers under the effect of stress in many unicellular organisms.

No lipid without stress...
Consisting of a "neutral lipid core", the droplet, which is formed mainly under the effect of stress, is surrounded by a simple layer of membrane lipids, itself encircled by proteins. When the stress disappears, the microalgae resume their growth by consuming the energy stored in the form of oils (triacylglycerols or TAGs). In order to be able to find a countermeasure to prevent the algae from degrading the valuable oils, researchers are trying to understand this degradation process in more detail.

 How to preserve lipids in the absence of stress
"To decipher this mechanism, we are studying algal mutants that show defects in the oil degradation process," explains Yonghua Li-Beisson, researcher and co-author of the discovery. "The one we identified has lost all these degradation capacities. We were able to demonstrate that this phenomenon is linked to the absence of a giant protein called DTH1 (Delayed in TAG Hydrolysis 1).

DTH1 is located on the lipid droplet by an amphipathic helix sequence and by binding to a specific phospholipid (phosphatidylethanolamine). "It's this combination that contributes to its association to LDs," Yonghua points out. "The dth1 mutant is unable to degrade the oils and moreover the mutant grew less well than its background strain. DTH1 is therefore a new protein essential to the degradation of lipid droplets that has been identified. This study was published in the Proceedings of the National Academy of Sciences USA at the end of August 2020 and opens up new perspectives in the development of 3rd generation biofuels.



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