IBM Research Europe

Biological remodelling of liquid water

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It is well known that the human body is mostly composed of water: The brain, for example, is 75 percent water and even bones are not “dry” – containing as much as one third water. All of this water maintains the shape and structure of biological cells and is involved in numerous biochemical processes. It is so important that reducing the amount of water in the body by only a few percent leads to dehydration, and a reduction in content by only 15 percent can be fatal.

The network of bonds in water nanoconfined in a cellular membrane

Even the search for life on other planets is largely a search for extra-terrestrial water. At the molecular scale, the role of water in biological phenomena remains under intense investigation. It is now clear that water is not a passive solvent in which biological molecules move and function, but an active driving force in the assembly and organization of proteins and membranes.

On the other hand, it has so far been acknowledged that only a very thin layer of water surrounding the (and in direct contact with) biological surfaces plays a relevant role in shaping biological phenomena. For this reason, such thin layer of water is known as “biological water” in the scientific community.

At the atomic level, water molecules become very slow and arrange in ordered patterns thanks to the formation of a peculiar network of bonds. Departing from the surface of biological systems, water molecules move and diffuse as they do in bulk water, i.e., in the absence of any biological system.

Recently a team from IBM Research Europe located in Daresbury, UK, the University of Oxford, and the University of Barcelona have explored the reverse question: How is water itself restructured in the vicinity of biological surfaces?

Reporting today, in the peer-review journal ACS Nano, the group use computational simulation at the molecular scale and innovative analysis tools to reveal how water structure responds to confinement by lipid (cellular) membrane surfaces – one of the most fundamental of all biological interfaces. The team find that water molecules are arranged in more ordered patterns and linked together by a peculiar network of bonds that extend at distances much larger than originally thought. The authors also identify the existence of an abrupt interface within the water layers separating so-called “bound” and “unbound” water both with structures which differ from normal liquid water.

These results provide new insight into the role of water in biological processes as well as in the concept of “biological water”, and show that water structure is highly responsive to environment – particularly when confined by the soft interfaces found near biological membranes.

The findings may have broader implications for developing nanoscale models of biological interactions and for understanding how alteration of the water structure and topology, for example, due to changes in extracellular ion concentrations, could affect diseases and signalling.

ACS Nano: Network Topology in Water Nanoconfined Between Phospholipid Membranes, Fausto Martelli, Jason Crain and and Giancarlo Franzese,

Research Staff Member, IBM Research Europe

Jason Crain

Leadership of research at the physics / life science interface ; Visiting Professor, University of Oxford, Department of Biochemistry, IBM Research Europe

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