New enzyme synthesized from scratch.

New Enzyme Synthesized From Scratch

Biological cells no longer hold a monopoly on enzyme design. After striving for years to break into this exclusive catalyst-creating territory, scientists seem finally to have made it. The achievement, they say, could lead to "designer enzymes" for specific medical, industrial or research uses.

In a biochemical tour de force, three Denver researchers designed and drew up blueprints for a hypothetical protein they predicted would act somewhat like the pancreatic digestive enzyme chymotrypsin. Then they chemically assembled their brainchild in the lab, and found that the synthetic molecule shows the predicted enzyme-like behavior.

Although others have assembled noncatalytic proteins with specific shapes (SN: 9/28/85, p.204) or commandeered biological cells to manufacture catalytic proteins, or enzymes (SN: 9/2/89, p.152), Stewart says his group is the first to both design and chemically synthesize an artificial enzyme from scratch.

"For the first time, we have shown that you can put together amino acids [the building blocks of proteins] in a designed structure and get a molecule with catalytic activity having the characteristics of an established enzyme," asserts biochemist John M. Stewart of the University of Colorado Medical School. Stewart, Karl W. Hahn and Wieslaw A. Klis detail the work in the June 23 SCIENCE.

Their synthetic enzyme, called chymohelizyme-1 (CHZ-1), began as a few lines on a computer screen. These represent the precise spatial arrangement of three pivotal amino acids in chymotrypsin's molecular structure that give the natural protein its catalytic powers.

Like archaeologists reconstructing entire skulls from a jawbone, the researchers built the entire 73-amino-acid protein around the catalytic fragment of chymotrypsin. Hahn spent two years designing CHZ-1 -- amino acid by amino acid -- with guidance from computer programs that use fundamental biochemical and thermodynamic theories to assess the physical viability of each new assembly proposed.

This modeling effort yielded a molecular blueprint comprising four parallel helical columns chemically tied together on one end. The other end of the columns hosts the catalytic triad of amino acids and an oily binding pocket for holding the synthetic protein's target molecules in place. It took Klis only one attempt, lasting about two months, to assemble molecules of CHZ-1 using techniques and machinery developed by Stewart and others. The team already has drawn up blueprints for other enzymes.

Biochemical studies indicate that CHZ-1 binds some target molecules as readily as chymotrypsin. Solutions containing CHZ-1 snip apart some targets about 100,000 times faster than catalyst-free solutions, though only about one-thousandth as fast as chymotrypsin solutions. CHZ-1 gets inhibited by the same agents that inhibit its natural counter-part, and it does not act on targets of related enzymes such as trypsin. In short, the humanly created protein behaves like a bona fide enzyme.

"It's the first clear-cut example of a de novo synthesis of a protein with catalytic activity," says protein chemist William F. DeGrado of Du Pont in Wilmington, Del.

Adds biochemist Bruce Merrifield of Rockefeller University in New York City, who won a 1984 Nobel prize for his work on protein synthesis, "If others can reproduce and expand on this work, it will be one of the most important achievements in biology or chemistry."