Cells in animals adhere to dynamic, seemingly random assemblies with other cells that make up tissues like skin, organs, and brain. The cell's adhesion and motion is controlled by the extracellular matrix, with the protein fibronectin being a key component. The proteins have optimal mechanical elasticity and also signal to cell surface receptors, integrins, the tension exerted on them. How this is achieved is the subject of an ongoing collaboration with the research group of Viola Vogel of the Department of Bioengineering at the U. of Washington in Seattle (see also Oct 2001 highlight). The most recent publication from this effort reports a 97,884 atom steered molecular dynamics simulation using NAMD. It is revealed now that stretching two consecutive domains of fibronectin deforms two sites, the so-called RGD and synergy sites as well as their distance. This weakens binding to cell receptors and, as a result, integrins can function as gauges that signal the magnitude of exterior forces to a cell.