Abstract
We were able to demonstrate that hydroxyectoine, in contrast to ectoine, is a good glass-forming compound. Fourier transform infrared and spin label electron spin resonance studies of dry ectoine and hydroxyectoine have shown that the superior glass-forming properties of hydroxyectoine result from stronger intermolecular H-bonds with the OH group of hydroxyectoine. Spin probe experiments have also shown that better molecular immobilization in dry hydroxyectoine provides better redox stability of the molecules embedded in this dry matrix. With a glass transition temperature of 87°C (vs. 47°C for ectoine) hydroxyectoine displays remarkable desiccation protection properties, on a par with sucrose and trehalose. This explains its accumulation in response to increased salinity and elevated temperature by halophiles such as Halomonas elongata and its successful application in ``anhydrobiotic engineering'' of both enzymes and whole cells.
Highlights
Compatible solutes are low-molecular mass water-binding organic solutes, which are accumulated in the cytoplasm of halophiles for osmotic equilibrium, either as a replacement for or in combination with inorganic salts
The sugars sucrose and trehalose, on the other hand, are well known desiccation protectants in all domains of life and their remarkable function has been linked to the ability to form glasses, which in selected cases ensures conservation of biological functions in an completely dry state
As the halophilic Halomonas elongata is unable to synthesize trehalose and/or sucrose, but appears to convert ectoine into hydroxyectoine in response to heat and water stress, we investigated whether this provides an alternative adaptation strategy for survival of cells and biomolecules in the dry state
Summary
Compatible solutes (organic osmolytes) are low-molecular mass water-binding organic solutes, which are accumulated in the cytoplasm of halophiles for osmotic equilibrium, either as a replacement for or in combination with inorganic salts. They are known as versatile stress-protecting compounds, in particular for the stabilization of proteins, membranes and whole cells. The sugars sucrose and trehalose, on the other hand, are well known desiccation protectants in all domains of life and their remarkable function has been linked to the ability to form glasses, which in selected cases ensures conservation of biological functions in an (almost) completely dry state This phenomenon of “anhydrobiosis” (life without water; Clegg, 2001) is apparent in many higher forms of life (e.g., seeds, resurrection plants, tardigrada, the chironomid Polypedilum vanderplanki). The outstanding role of disaccharides (possibly in combination with intrinsically disordered proteins, IDPs) has given rise to a number of biophysical models, of which the “water entrapment” (Belton and Gil, 1994; Cottone et al, 2002) and “anchorage” hypothesis (Allison et al, 1999; Francia et al, 2008) are the most comprehensive because they encompass glassformation of solutes and simultaneous entrapment of small water clusters, possibly anchored to critical sites at the interface with biomolecules
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