Abstract
Ectoine, a compatible solute and osmolyte, is known to be an effective protectant of biomolecules and whole cells against heating, freezing and extreme salinity. Protection of cells (human keratinocytes) by ectoine against ultraviolet radiation has also been reported by various authors, although the underlying mechanism is not yet understood. We present the first electron irradiation of DNA in a fully aqueous environment in the presence of ectoine and at high salt concentrations. The results demonstrate effective protection of DNA by ectoine against the induction of single-strand breaks by ionizing radiation. The effect is explained by an increase in low-energy electron scattering at the enhanced free-vibrational density of states of water due to ectoine, as well as the use of ectoine as an ˙OH-radical scavenger. This was demonstrated by Raman spectroscopy and electron paramagnetic resonance (EPR).
Highlights
Ectoine, a compatible solute and osmolyte, is produced and accumulated at molar concentrations by halotolerant and halophilic microorganisms to survive in extreme environments with high salinity.[1,2] This is achieved by keeping the chemical potential of water in- and outside the cell in balance, without adjusting salt concentrations.[2]
To quantify the relative contributions of the different protective mechanisms further work is needed. This raises a fundamental question of radiation biology, namely the quantitative contributions of high energy radiation, low energy electrons, prehydrated electrons and OH-radicals to the total damage yield
A viable approach to answer this question in future studies might be to perform low-energy electron irradiation experiments at specific electron energies in the condensed phase with different levels of hydration.[36]
Summary
A compatible solute and osmolyte, is produced and accumulated at molar concentrations by halotolerant and halophilic microorganisms to survive in extreme environments with high salinity.[1,2] This is achieved by keeping the chemical potential of water in- and outside the cell in balance, without adjusting salt concentrations.[2]. We present a study which aims at obtaining a better understanding of the interplay between DNA, ectoine, sodium chloride, water and ionizing radiation. We irradiated DNA with high energy electrons (30 keV) in phosphate buffered saline (PBS) at various ectoine (0–1 M) and sodium chloride (0, 0.5 M) concentrations. The results show a significant protection of DNA against induction of SSB by ionizing radiation and a small protective enhancement upon the addition of NaCl. Further measurements were performed to investigate the underlying mechanisms. The increase of the free vibrational density of states of the water molecules due to the presence of ectoine was measured by Raman spectroscopy, and was related to an increase of the inelastic scattering cross section of the secondary radiation products. The results are compared with the above mentioned previous studies and interpreted in terms of protective mechanisms
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