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A single water molecule acting as gate keeper

November 12, 2004

How do the bonds cells form with their environments rupture? What enables some cells to migrate? It is known since quite a while that cells can have complex mechanical interactions with their environments. Not only the biochemical but also the physical properties of their environment can thus have significant impact on cell behavior and even gene expression.

Together with fellow researchers at the University of Washington in Seattle, David Craig, and the Beckman Institute in Urbana-Champaign (USA), Klaus Schulten and Mu Gao, ETH Professor Viola Vogel explored the mechanical interactions between cells and their extracellular matrices. They wanted to know how the bond between the proteins which anchor cells in their environment ruptures if exposed to tensile forces.

They show in the current issue of the journal "Structure" that a single water molecule acts as a gate keeper. It protects the forcebearing bond between the cell and the extracellular matrix from attacks by free water molecules and thereby delays the rupture.

Dynamic picture of the anchoring bond under force

Integrins are transmembrane proteins which anchor cells to the extracellular matrix by specific bind to short tri-peptides, i.e. matrix exposed RGD-peptides. The researchers tested the mechanical properties of this bond using computer simulations.

They placed the integrin domains which bind the RGD-peptide into a box filled with water molecules and applied force between the integrin and the RGD-peptide. These simulations give the first dynamic picture how the integrin-RGD complex resists force-induced dissociation.

Such simulations allow watching the movement of all water molecules and atoms of the protein complex under the influence of tensile forces acting on the integrin-RGD complex. They rev�ealed that a single water molecule makes a major contribution to the mechanical stability of the most critical force-bearing linkage. The RGD-integrin complex is only formed in the presence of a doubly charged calcium or manganese ion. A single water molecule is tightly bound to this ion and thereby blocks access of free water molecules to the force bearing bond of the RGD-integrin complex.

Broader significance

While the regulatory functions of divalent ions in biological processes are well known, the insights into the dynamic processes of the RGD-integrin rupture described in the current issue of "Structure" provide for the first time a structural basis how the bond between cells and their environments is stabilized mechanically. Such dynamic insights might have broader implications. This includes the development of new drugs or for understanding the processes how cells attach to and detach from the surrounding tissue, how they migrate and - in case of cancer - how they are stimulated to form new blood vessels.

ETH Zuerich

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