Heralding a major advance in the field of protein engineering, scientists at the University of California, Berkeley have designed a protein that toggles between two different structures upon binding a small molecule. The designed property is significant because many biological processes depend on a protein's ability to change its shape in response to outside signals. The scientists predict that with further refinements, their protein may one day be used to detect environmental toxins or--in a laboratory setting--act as a switch to activate genes or as a molecular zipper to join together proteins.

The newly designed structure is featured in the cover article of the June 1996 issue of Nature Structural Biology.

"This designed protein is novel because it responds to its environment by undergoing a dramatic structural change," said Dr. Tom Alber, an x-ray crystallographer and the study's lead scientist.

The scientists synthesized their own version of a common protein structure called a double-helical coiled coil. This structure is composed of two helices that wrap like grape vines around each other. The design incorporated a selective binding site such that when the researchers added a small molecule, benzene, the two helices intertwined with a third to create a triple-helical coiled coil.

This structural change could enable the protein to indicate the presence of benzene, which is a carcinogen, said Dr. Alber. Additional proteins could be designed to detect other environmental pollutants--but not quite yet. "The present design binds compounds such as benzene too weakly to beat your nose as a detection system," said Dr. Alber.