Catalytic antibodies do greasy work.

Catalytic antibodies do greasy work

Two years ago, researchers first reported getting antibodies to act like enzymes, proteins that catalyze specific chemical reactions. Since then, scientists have designed many catalytic antibodies, known also as abzymes. Each is tailor-made to do a specific chemical job, such as slicing one molecule in two or splicing two molecules into one. Now a team of six scientists has coaxed abzymes into doing something new -- work in a greasy, organic environment that normally would deactivate them. The team describes its strategy in the Dec. 21 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY.

Researchers predict that catalytic antibodies will become versatile tools for such jobs as purifying drugs, cutting and splicing proteins and destroying viruses. To date, abzyme research largely has been limited to reactions that occur in aqueous solutions. But the ability to use abzymes in organic solvents could make them handy for a variety of reactions that occur only in organic solutions, says Richard J. Massey, a coauthor of the report and vice president of IGEN, Inc., a biotechnology firm in Rockville, Md.

The scientists first load the antibodies into the watery interiours of greasy, microscopic spheres, called reverse micelles, that dissolve in organic solvents. The solvent used here is isooctane. A reactant chemical, dissolved in the isooctane, penetrates into the reverse micelles, where the abzymes catalyze reaction, in this case cleaving the phenylacetate molecules. "This gets across the concept that we think will be important, namely, the ability of an antibody to work in an organic solvent," Massey says.

Catalytic antibodies and other enzymes speed the transformation of a chemical reactant into a product. Presumably, they achieve this by binding to the reactant and encouraging the formation of what chemists call the reaction's "transition state," a short-lived, intermediate chemical structure that, once formed, quickly yields the product molelcule(s). Enzymes speed reactions by getting reactants into their transition states faster. To make an abzyme that specifically cleaves phenylacetate, the researchers obtained antibodies that bind to another longer-lived molecule that is similar in form to phenylacetate's fleeting transition-state.

Since all antibodies are structurally similar, the scientists expect that their success at getting the phenylacetate-cleaving abzyme to work in a reverse micelle will extend to other abzymes. And since the researchers can use well-established methods for obtaining antibodies to a variety of transition states, they expect the technology to have many applications. One possible use is to purify drugs that emerge from their chemical syntheses in two mirror-image forms, only one of which is active. By binding to and breaking up only the inactive form, abzymes might held drug companies purify their products, Massey says.

The researchers admit that hurdles remain ahead. Most abzymes made so far work at a snail's pace compared with the enzymes found inside cells. Also, most existing abzymes cut molecules in two. Peter G. Schultz of the University of California, Berkeley, an author of the recent paper and one of the earliest to study catalytic antibodies, says it is harder to make abzymes that splice together smaller molecules. Stephen J. Benkovic, a catalytic-antibody specialist at Pennsylvania State University, adds that it may be harder to get molecules that are "greasier" and even less water-soluble than phenylacetate to go inside the reverse micelles.