Is Water Essential to Life?

Image of a water molecules composed of 2 hydrogen atoms and 1 oxygen atom. Water molecules are polar, resulting in a partial negative charge near the oxygen atom and partial positive charges near the hydrogen atoms. This uneven distribution of charge causes water molecules to attract one another – forming the ‘hydogen bond’ shown above. Hydrogen bonds are what give water unique properties that are thought to be essential for water’s role in making life on Earth possible. Credit: University of Arizona

New research by scientists at the University of Bristol has challenged one of the key beliefs in chemistry: that proteins are dependent on water to survive and function. The team’s findings, published this month in Chemical Science, could eventually lead to the development of new industrial enzymes.

Proteins are large organic molecules that are vital to every living thing, allowing us to convert food into energy, supply oxygen to our blood and muscles, and drive our immune systems. Since proteins evolved in a water-rich environment, it is generally thought that they are dependent on water to survive and function.

Proteins consist of one or more polypeptides – chains of amino acids held together by peptide bonds. If a protein in water is heated to temperatures approaching the boiling point of water, these chains will lose their structure and the protein will denature (unfold).

A classic example of denaturing occurs when an egg is hard-boiled: the structures of the proteins in the egg unfold with temperature and stick together creating a solid. In the egg’s case, this process cannot be reversed – however there are many examples where cooling the protein results in refolding of the structure.

Previously, it was thought that water was essential to the refolding process, however the Bristol findings suggest this isn’t necessarily the case.

Using a spectroscopic technique called circular dichroism, Adam Perriman of Bristol’s School of Chemistry and colleagues have shown that the oxygen-carrying protein myoglobin can refold in an environment that is almost completely devoid of water molecules.

Our planet is at just the right distance from the Sun for liquid water to exist on its surface and play a role in life. But are their other options for life? Image: NASA

“We achieved this by attaching polymer molecules to the surface of the protein and then removing the water to give a viscous liquid which, when cooled from a temperature as high as 155°C, refolded back to its original structure," said Perriman.

“We then used the Circular Dichroism beamline (B23) at Diamond Light Source, the UK’s national synchrotron science facility in Oxfordshire, to track the refolding of the myoglobin structure and were astounded when we became aware of the extremely high thermal resistance of the new material.”

These findings could pave the way for the development of new industrial enzymes where hyper-thermal resistance would play a crucial role, in applications ranging from biosensor development to electrochemical reduction of CO2 to liquid fuels.

Reference:
Hyper-thermal stability and unprecedented re-folding of solvent-free liquid myoglobin’ by Alex Brogan, Giuliano Siligardi, Rohanah Hussain, Adam Perriman and Stephen Mann in Chemical Science DOI: 10.1039/C2SC20143G