University of Utah researchers bridge the gap between atomic-scale simulations and whole-cell models.

According to the old adage, oil and water don't mix. As simple as it sounds, this principle is the construction secret behind one of evolution's most successful structures--the cell membrane. It acts as both guardian and gate, controlling what nutrients and ions, chemical messages, and drugs pass into and out of the cell.

To do its job, the cell membrane must be strong yet flexible, fluid yet robust. It must shrink, bend, and swell like a rubber ball in response to changes in its contents and the external environment. This elasticity allows it to protect the building blocks essential to all organisms--genes and organelles, nutrients and energy--against the hostile world outside.

Understanding how cell membranes accomplish these feats would help scientists design more efficient drug delivery systems, develop accurate models of cellular function, and better understand basic biochemical processes such as ion transport. The small size of cells, however, makes it problematic to observe the behavior of real cell membranes in laboratory experiments. Determining both how easily a membrane expands and contracts and how a membrane's composition affects its elasticity demands pricey equipment and impeccable technique.

The alternative is to run experiments on virtual cells. Using a computer, scientists can observe the behavior of every atom in a cell membrane and its surrounding solvent. Rather than inferring what the molecules are doing from laboratory results, researchers using molecular dynamics simulations can observe all the molecular interactions firsthand. This method allows them to trace membrane behaviors back to the movements of a few constituent molecules. But molecular dynamics modeling comes with its own set of difficulties. Because cell membranes have a relatively large surface area, the number of molecules required to model an entire cell membrane plus its surrounding solvent molecules is unbelievably high. Not even a supercomputer can keep track of all the atoms involved.

Now chemistry professor Gregory Voth and research assistant professor Gary Ayton of the University of Utah have found creative ways to sidestep this problem. Using methods typically applied in statistical mechanics and engineering, they have been able to bridge the gap between atomic-scale simulations and whole-cell membrane models. The results, obtained on Alliance supercomputers, represent views of cell membrane behavior unparalleled in any petri dish.

Access Online | Posted 8-8-2003