Magazine article Science News

Material Peptide: A Piece of Protein Yeast Becomes a Building Block for Scientists

Magazine article Science News

Material Peptide: A Piece of Protein Yeast Becomes a Building Block for Scientists

Article excerpt

A piece of yeast protein becomes a building block for scientists

Four years ago, Shuguang Zhang was a typical molecular biologist. Questions about the replication of genetic material occupied most of his waking hours and all of his lab work at the Massachusetts Institute of Technology.

Now, thanks to his son's Lego set, he finds himself more and more drawn to materials science.

Those plastic building blocks provide never-ending entertainment for children. Pegs jutting out of each block's top fit into indentations on the undersides of other blocks, making possible the construction of towers and structures of all sorts.

Zhang and his MIT colleagues recently discovered that nature has created its own set of molecular Legos and hidden them away in a peculiar yeast protein. Each of these "Legos" consists of a string of 16 amino acids, which together form a type of molecule known as a peptide. Peptides serve as the building blocks for proteins.

From the biologist's viewpoint, the newly identified peptide may provide clues about certain disease processes, says Zhang. These peptide molecules interlock with each other to create structures resembling the proteinaceous plaques found in the brains of people with Alzheimer's disease and in the livers of people with cirrhosis.

Peptides that readily fit together to form bigger structures might also help explain how life originated. Perhaps, Zhang speculates, collections of peptides like these assembled into primordial, cell-like compartments.

But the Lego peptide also shows potential in disciplines traditionally far removed from biology. Increasingly, materials scientists seek molecules that they can piece into ever more complex and useful entities. This approach leads to new materials for all sorts of structural, mechanical, and biomedical applications.

"The overall objective is to do things from the molecular scale up," explains Stephen A. Fossey, a materials engineer at the U.S. Army Natick (Mass.) Research, Development, and Engineering Center. Some materials researchers have begun to eye biological molecules in their quest for easy-to-use building blocks and for guidance on how these starting molecules should fit together (SN: 2/23/91, p.119; 4/20/91, p.246; 5/16/92, p.328).

Like most biologists, however, Zhang had focused on how proteins and other molecules function in living cells. Several times during the past four years, he found himself at apparent dead ends in his investigations of the yeast protein and its unusual peptide fragment. But when viewed instead from the perspective of materials science, those same efforts represent an exciting success story.

"It's a very interesting observation," comments David A. Tirrell, a polymer chemist at the University of Massachusetts at Amherst. He, too, studies peptides, but primarily with the goal of making new materials. "By our standards, this [peptide] is a relatively complicated polypeptide chain. It has relevance both to the design of synthetic materials that self-assemble and to [biological questions]."

With the newly discovered peptide or other molecules like it, scientists might one day build "natural" drug-delivery platforms or other implantable devices whose degradation would leave no foreign matter behind in the body, suggests Alexander Rich, a biophysicist at MIT.

Zhang's divergence from the field of molecular biology began with the discovery of the protein that contains this amino acid sequence. Working with Rich, he was looking for proteins that bind to a special form of DNA, called Z-DNA.

Z-DNA twists in the opposite direction from the typical, right-handed double helix, known as B-DNA. The left-handed conformation requires quite a bit of extra energy to keep from reverting to a right-handed twist, notes Zhang.

The discovery of left-handed DNA some 14 years ago puzzled scientists, who until then thought DNA had only one conformation. …

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