Neutrons describe ectoine effects on water H-bonding and hydration around a soluble protein and a cell membrane

Abstract

Understanding adaptation to extreme environments remains a challenge of high biotechnological potential for fundamental molecular biology. The cytosol of many microorganisms, isolated from saline environments, reversibly accumulates molar concentrations of the osmolyte ectoine to counterbalance fluctuating external salt concentrations. Although they have been studied extensively by thermodynamic and spectroscopic methods, direct experimental structural data have, so far, been lacking on ectoine-water-protein interactions. In this paper, in vivo deuterium labeling, small angle neutron scattering, neutron membrane diffraction and inelastic scattering are combined with neutron liquids diffraction to characterize the extreme ectoine-containing solvent and its effects on purple membrane of H. salinarum and E. coli maltose binding protein. The data reveal that ectoine is excluded from the hydration layer at the membrane surface and does not affect membrane molecular dynamics, and prove a previous hypothesis that ectoine is excluded from a monolayer of dense hydration water around the soluble protein. Neutron liquids diffraction to atomic resolution shows how ectoine enhances the remarkable properties of H-bonds in water—properties that are essential for the proper organization, stabilization and dynamics of biological structures.

DNA protection by ectoine from ionizing radiation: molecular mechanisms

“…36 Ectoine is known to be expelled from the first hydration shell of charged surfaces and biomolecules. 6,7,11 However, its presence in solution will inevitably decrease the amount of water around DNA in the biologically relevant target volume of 10-15 nm diameter. 20,37 Therefore, ectoine may act as a protective agent by passively displacing water from the surroundings of the DNA.…”

“…3) in the solid 4 state and in water, 5 exerts a kosmotropic effect on the local water structure [5][6][7][8] as well as an influence on protein functions. 7,[9][10][11] Moreover, various studies [12][13][14] investigated the effects of ectoine on biological damage caused by ultraviolet radiation (UV) of various wavelengths. The study by Bünger et al 13 found that UV-A (340-400 nm) irradiated human keratinocytes show a decrease in mitochondrial DNA mutations for cells pretreated with ectoine.…”

Ectoine as a promising protective agent in humans and animals

“…Interestingly, this amino acid derivative does not interact directly with protein surfaces but rather it forms a molecular net holding water molecules close to the macromolecule (10,18,19). Moreover, Roychoudhury et al (20) have shown that ectoine, like other compatible solutes, strengthens intramolecular interactions essential for protein stability.…”

“…Harishchandra et al (28) propose that ectoine increases cell membrane fluidity to cope with extreme conditions such as high temperature or osmotic pressure. A recent biophysical study by Zacchai et al (10) showed that ectoine is excluded from the hydration layer at the membrane surface and does not affect membrane molecular dynamics. Moreover, improved hydration of the cell surface thanks to ectoine increases intermolecular spacing and boosts the mobility of the lipid head groups in the cell membrane ( Figure 2) (29).…”

“…A number of biophysical studies show that ectoine binds water molecules even better than some other osmoprotectants such as glycerol (9,10) and that it is well tolerated by humans, animals, and various cell cultures. In fact, ectoine retains strong hydration properties even at high NaCl concentrations (11).…”