Abstract
Deep subsurface environments can harbour high concentrations of dissolved ions, yet we know little about how this shapes the conditions for life. We know even less about how the combined effects of high pressure influence the way in which ions constrain the possibilities for life. One such ion is perchlorate, which is found in extreme environments on Earth and pervasively on Mars. We investigated the interactions of high pressure and high perchlorate concentrations on enzymatic activity. We demonstrate that high pressures increase α-chymotrypsin enzyme activity even in the presence of high perchlorate concentrations. Perchlorate salts were shown to shift the folded α-chymotrypsin phase space to lower temperatures and pressures. The results presented here may suggest that high pressures increase the habitability of environments under perchlorate stress. Therefore, deep subsurface environments that combine these stressors, potentially including the subsurface of Mars, may be more habitable than previously thought.
Highlights
Deep subsurface environments can harbour high concentrations of dissolved ions, yet we know little about how this shapes the conditions for life
Though there is quite a lot known about the effects cellular organic osmolytes, such as trimethylamine-N-oxide, impose on organisms thriving in the deep sea under high-pressure stress up to the 1000 bar level[10,11,12], the combined effects of high salt, low temperature, and high pressure on biochemical processes is still terra incognita
A marked destabilising effect of perchlorate, being a typical low-charge-density anion at the far end of the Hofmeister series of anions, at high concentrations, has been observed in lysozyme at pH 7 as well and is expected to be due to weak binding of the ClO4− anions to the protein[36,37]. This reduces the Little is known about the effects of high ion concentrations on cellular life or the combined effects of ions with high pressure
Summary
Deep subsurface environments can harbour high concentrations of dissolved ions, yet we know little about how this shapes the conditions for life. We know even less about how the combined effects of high pressure influence the way in which ions constrain the possibilities for life One such ion is perchlorate, which is found in extreme environments on Earth and pervasively on Mars. These may take the form of the reported subglacial lake at the Martian south pole[3], or the deep groundwater beneath the Martian cryosphere[2] These cold environments have been hypothesised to contain high concentrations of perchlorate salts, following their detection at the surface[6], due to their extremely low eutectic temperatures. Previous studies have demonstrated the deleterious effects of destabilising ions such as perchlorates on the activity of αchymotrypsin (α-CT) and other enzymes[7,13] Stabilising salts, such as sodium sulphate[14], have been shown to increase the activity and structural stability of α-CT15. A greater understanding of how these effects change with pressure is yet to be achieved
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