Monolayers reveal protein preferences.

The chemical complexity of proteins makes them seem quite fickle to bio-engineers. On one hand, these molecules often stick to surfaces where they don't belong, fouling contact lenses or leading to clots in artificial blood vessels, implanted valves and otehr biomedical devices. On the other hand, they sometimes don't stick as well as researchers would like, as in procedures for purifying biotechnology's protein products.

Now, two scientists at Harvard University have developed a technique for figuring out just what makes one protein favor some surfaces over others. In the May 24 SCIENCE, chemist George M. Whitesides and graduate student Kevin L. Prime report developing organic films to test how well proteins stick to different materials.

To make the films, Prime and Whitesides add hydrocarbon molecules called alkanes to an alcohol solution containing a thin strip of gold. The alkanes self-assemble on the gold template and form a single, dense layer of molecules. For their experiments, the researchers used alkanes with methyl, sugar, hydroxyl and polyethylene glycol tails that stick up from the monolayer. This enabled them to create monolayers with known surface structure and composition. They then added various proteins to determine how much each monolayer film absorbed.

"Proteins are complex, so if you can minimize the complexity of the solid surface, then you have a chance to correlate the solid surface's properties with what [absorption] you see," notes bio-engineer Joseph Andrade of the University of Utah in Salt Lake City, who also studies protein/surface interactions. "The self-assembled monolayer system provides a degree of control, reproducibility and reliability that is simply unavailable with all other systems."

Whitesides and Prime observed that the five proteins they studied stuck poorly to films containing lots of polyethylene glycol. This tail is so bulky that it forms a slick gel that proteins cannot penetrate. But the proteins seemed to take a fancy to the other films, which readily absorbed the added molecules.

"Now we can understand on a molecular level the interaction of proteins which man-made materials," Whitesides told SCIENCE NEWS. In the past, chemists have relied mostly on trial and error to identify "nonstick" surfaces that absorb less protein. But with the new data, researchers can develop " a prescription for how to modify these surfaces to improve them," Whitesides says. "We want to develop man-made materials that are as non-interactive as possible."