Protein-Like Molecules Could Form Medical Devices, Electronics

"Proteins come in so many shapes and sizes that they are able to perform a wide variety of functions," said Jonathan Parquette, assistant professor of chemistry at Ohio State. "We wanted to mimic that versatile structure in a synthetic form."

Parquette and his students built the molecules, called dendrimers, from tiny, spaghetti-like plastic filaments. Researchers have long tried to mimic the shape of proteins using dendrimers, but the Ohio State group is the first to coax the soft, tangled filaments to maintain a shape that suits needed applications.

The molecule is shaped like a sphere, supported by branching beams of polymer inside, with hollow portions that could theoretically hold drugs or other chemicals. Parquette described his work September 23 at the BioMEMS and Biomedical Nanotechnology World 2001 meeting in Columbus, Ohio.

BioMEMS, or biomedical microelectromechanical systems, are microscopic medical devices under development around the world. The tiny devices can be as small as a few millionths of a meter -- much smaller than the width of a human hair.

Parquette's synthetic protein molecule belongs to the realm of nanotechnology, which concerns devices even smaller than bioMEMS. The molecule is about the same size as a small protein or a short sequence of DNA -- a few tens of atoms across.

The chemists are working toward developing the molecule into a larger, more complex structure.

Ultimately, synthetic proteins could act as devices to deliver medicine to tumors or other sites of disease in the body. They could also act as catalysts for chemical reactions that produce drugs, or form computer chips for light-responsive molecular electronics.

For these molecules to perform such tasks, the outer shell would have to open and close on cue, Parquette explained. A molecule could locate a tumor, for instance, and unravel its structure to release cancer-fighting medicine from within.

"Along the outside of the molecule, the atoms fasten together like a zipper," Parquette explained. "Getting them to zip up is half the puzzle. Getting them to unzip on demand is the other half."

With chemicals, the researchers caused the normally long, stringy dendrimers to fold into a protein-like shape. Then they added other chemicals that bound themselves to select sites along the dendrimers, effectively zipping together layers of folds and stiffening the structure overall.

Currently, Parquette and his colleagues are investigating whether light could be used as a stimulus to make the dendrimers unfold. If so, the protein-like molecules could form the basis for extremely tiny, very fast computer chips.

Whereas semiconductor computer chips carry a digital signal of "one" or "zero" based on the presence of an electron, molecular computer chips stimulated by light from fiber optics could carry a signal based on whether individual molecules were "zipped" or "unzipped."

For Parquette, this work has helped to explain how nature builds its own micrometer- and nanometer-size structures.

"On the nanoscale, it seems that atoms have a way of cooperating together to assume certain structures for specific functions. If we can learn to harness that cooperativity, we may be able to form better synthetic molecules," Parquette said.

"As soon as you think you're pretty smart about something, it turns out nature has thought of it first," he said with a smile.

This work was supported by Parquette's Faculty Early Career Development (CAREER) award from the National Science Foundation.