Scientists have created a new family of artificial enzymes that can build important chemical bonds with extremely high precision.
The advance could eventually provide cleaner and more efficient ways to manufacture medicines, specialty chemicals and advanced materials.
Researchers at the Manchester Institute of Biotechnology developed the engineered enzymes to create carbon-carbon and carbon-nitrogen bonds.
These bonds form the basic framework of countless molecules, but constructing them in exactly the right arrangement can be challenging.
The research, led by Dr. Zachary Birch-Price and Professor Anthony Green, was published in Nature Catalysis.
Enzymes are biological catalysts that speed up chemical reactions. They are widely used in modern biotechnology because they can often perform reactions under mild conditions and with remarkable selectivity.
However, natural enzymes evolved to perform particular biological jobs, meaning that many reactions useful to chemists are outside their normal abilities.
The Manchester researchers wanted to expand what enzymes can do.
Instead of relying entirely on the amino acids normally found in proteins, they engineered enzymes containing a non-natural catalytic amino acid. This gave the proteins chemical abilities that natural enzymes generally do not possess.
The researchers named the resulting family of enzymes “allylic transferases.”
During a reaction, these enzymes produce a highly reactive intermediate molecule inside their active site—the small region where chemical reactions take place. Different carbon- or nitrogen-containing molecules can then react with this intermediate, allowing the enzyme to create a variety of new carbon-carbon and carbon-nitrogen bonds.
Importantly, the same basic enzyme system could work with many different chemical starting materials. The researchers tested compounds including furans, indoles, pyrroles and anilines, demonstrating that the approach can produce a diverse collection of molecular structures.
The team then used a process called directed evolution to improve the enzymes. This technique mimics natural evolution in the laboratory.
Researchers create different versions of an enzyme, test their performance and use the most successful versions as the basis for further improvements.
One evolved enzyme, called ASB1.3, converted more than 99% of starting material into desired products in several experiments while also producing molecules with very high stereochemical purity. This is important because molecules containing the same atoms can have different three-dimensional arrangements, and only one form may have the desired properties.
Another enzyme, ASA1.5, successfully created particularly challenging structures known as all-carbon quaternary stereocenters. In larger laboratory-scale experiments, it achieved 98% conversion.
The researchers also found remarkably few unwanted products. Across the reactions they examined, the enzymes generally produced one major desired product rather than mixtures requiring complicated purification.
Structural studies offered clues about how the enzymes achieve such precision. A molecule released during the reaction appears to remain temporarily inside the enzyme and help position incoming molecules in the correct orientation.
The technology will require further development before it can be widely used in industrial chemical production. However, the researchers say the study demonstrates how combining protein engineering with chemistry not normally found in nature can dramatically expand the abilities of enzymes.
Ultimately, such designer enzymes could give chemists a powerful new toolbox for constructing complex molecules more selectively and efficiently, including molecular structures that are difficult to make using conventional chemical catalysts.
