Changing the spatial arrangement of molecules in a cell can alter their functions.

In biology, location matters. A cell's strategically placed organelles don't behave the same if they are suspended in a test tube. A gene carefully enveloped in a cell's nucleus doesn't remain functional if it's floating outside the nucleus. And a protein that normally moves long distances to do its job doesn't succeed if it's tied to one spot.

Biologists readily accept the general principle that location is intricately tied to function. Quantifying this is hard, however. There has been no well-established method to tweak a protein's location. But now, HHMI investigator Jay Groves has a technique to do just that. And the results he's getting from his experiments suggest just how important spatial organization of molecules inside cells is to human health, with implications for the immune system and cancers.

Groves and his lab members at the University of California, Berkeley, call their method "spatial mutation." While a typical protein mutation changes the overall sequence and structure of a protein, a spatial mutation changes its positioning in cells, along with its ability to move and organize.

Groves relies on a diverse lab team of biochemists, engineers, and physicists to perform these experiments. Groves did his graduate work in soft condensed matter physics—essentially, the study of materials that are soft and squishy, such as membranes. As a biophysics graduate student at Stanford University, he designed systems that allowed him to round up various membranes into discrete areas. He decided to try the technique on living biology.

"Biologists were starting to ask questions about large-scale organization that couldn't be answered by the classical tools of biology," says Groves. He suspected his method of divvying up membranes into compartments could be used to block the movement of membrane-embedded proteins. "I realized that I could get inside a cell and rearrange the organization."

He chose to study signaling between two membrane-embedded proteins, known as juxtacrine signaling. Two cells must come in close contact for this type of communication; they can't pass the chemical signal through space. Groves envisioned having one protein on a controllable synthetic membrane while its partner protein was on the membrane of a living cell.

To set up a spatial mutation, Groves and his collaborators begin with a glass slide and painted a nanometer-scale grid of metal lines on the glass using a technique (electron-beam lithography) borrowed from the computer chip industry. Then they arrange lipids—the building blocks of cellular membranes—and the embedded protein of interest within each square of the grid. Although free to move within its square of the grid, a protein can't pass the metal line, where there's a brief break in the lipids. The set-up thwarts any long-distance movement or large-scale organization of the proteins while local rearrangement and clustering are allowed to occur normally.

Image: Groves Lab

	PAGE 1 of 2	Continue