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The STUDIA UNIVERSITATIS BABEŞ-BOLYAI issue article summary
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Abstract: When exposed to high osmolarity/salinity environments, many Bacteria and Archaea counteract the ensuing dehydration of the cytoplasm and drop in vital turgor though the accumulation of a selected class of organic osmolytes, the compatible solutes. These compounds are highly compliant with cellular physiology. In addition to their crucial role in cellular osmotic adjustment, they also serve as chemical chaperones by promoting the functionality of cellular components, macromolecular complexes, and even of entire cells from various types of insults. Ectoine and its derivative hydroxyectoine are prominent members of the compatible solutes. Their biosynthetic genes (ectABC/D) are widely found in members of the Bacteria (Czech et al., 2018), occur only rarely in Archaea (Widderich et al., 2016) and, surprisingly, have now also been detected in a few halophilic ciliates. It seems that the ect genes-containing Archaea and ciliates have acquired the ability to produce ectoines via horizontal gene transfer events (Widderich et al., 2016; Czech & Bremer, 2018). Ectoines can be amassed by osmotically stressed cells through import and synthesis. I will discuss various types of ectoine/hydroxyectoine importers with special emphasis on the substrate-binding-proteins of ABC- and TRAP-type transporters as their crystal structures revealed the molecular determinants of how compounds that are otherwise preferentially excluded from protein surfaces can nevertheless be bound with high affinity and specificity (Hanekop et al., 2007; Lecher et al., 2009). In addition, I will present an overview of the biochemistry and structural biology of the ectoine/hydroxyectoine biosynthetic enzymes (Höppner et al., 2014; Czech et al., 2019), and discuss the osmostress-responsive expression of the ect biosynthetic genes (Czech et al., 2018).
Keywords: ectoine, gene regulation, hydroxyectoine, osmotic stress, synthesis, transport. |
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