Cell membranes change the structure of water at least twice as far as expected

A new study published in ACS Nano shows how water is restructured in the vicinity of biological membranes. “The results provide a new insight into the role of water in biological processes, showing that water is highly responsive to the environment – particularly at the soft interfaces given by biological membranes”, explains Giancarlo Franzese, researcher at the Institute of Nanoscience and Nanotechnology (IN2UB) and the Department of Condensed Matter Physics of the University of Barcelona, who led the study within a collaboration with a team from IBM Research Europe (Daresbury, UK) and the University of Oxford.

The common understanding to date was that it was only a thin layer –of about 1 nm– of water in direct contact with membranes which played a role in shaping biological phenomena. This layer is sometimes called biological water and its dynamics and structure are very different from bulk water.

At an atomic level, biological water is very slow, bounded to the membrane, and forms a peculiar network of bonds. At approximately 0.8 nm from the membrane, the authors identified the existence of an abrupt bound–unbound water interface. Unbound water molecules move and diffuse as they do in bulk water, i.e., in the absence of any biological system. However, unbound water has many more defects than bulk water up to a surprisingly large distance, 2.4 nm away from the membrane, corresponding to eight water layers.

Researchers used computational simulation at a molecular scale and innovative analysis tools to reveal how water structure responds to confinement by lipid cellular membrane surfaces. “Despite the defects, unbound water is more ordered than bulk water and has a characteristic topology that extend at distances much larger than originally thought” points out Franzese.

The results of the study offer a new perspective on studying nanoconfined water and developing models of biological interactions. It helps in the understanding, for example, of the relation between changes in water structure, due to extracellular ions, and diseases or cell signaling.

Article reference:

F. Martelli, J. Crain i G. Franzese. «Network Topology in Water Nanoconfined between phospholipid membranes». ACS Nano, Juny 2020. Doi: /10.1021/acsnano.0c02984