In a new study that may provide a defense against biochemical warfare, researchers at Texas A&M University have modified an enzyme to destroy harmful nerve agents 15,000 times more effectively than the wild-type parent.
In a paper published in Biochemistry (1), the group reported their enhancement of the active site of an enzyme called phosphotriesterase (PTE) by mutagenesis. These mutations improved the enzyme’s ability to hydrolyze or decompose the more toxic variants of chemical warfare agents.
To improve the enzyme’s activity, Raushel’s lab used a technique called directed evolution. By imitating the natural selection process, the researchers created libraries of mutant enzymes and tested the activities of those mutated enzymes to select the ones that degraded the lab’s nerve agent analogs most effectively. Then, those selected enzymes were used as parents for the next generation of mutants that would include a subset of enzymes that were even more effective in the task.
“In one sense you mimic nature by taking the ones that are better and making further mutations of those until you find something that’s quite reasonable. So, in the best case here for the compounds that we were initially looking at relative to the wild-type enzyme, we’ve improved the catalytic constants by a factor of 15,000,” said Raushel.
While the research may eventually provide practical applications in military defense and broader commercial use in the future, the lab has only done preliminary analog testing at this point. Right now, his lab lacks access to actual military nerve agents, which has limited the testing of the newly modified PTE enzymes onsite.
“Our strategy is that we use analogs to make better mutants, and then take the best mutants and have them tested at [U.S. Army facility] Aberdeen Proving Ground,” explained Raushel. “Then, we can make further changes based on the ones that work better with the compounds that they have there.”
In addition to these tests, Raushel’s team is now in the process of conducting experiments to make the PTE enzyme much more specific for the hydrolysis of an extremely toxic individual nerve agent used in chemical warfare called VX. At the moment, there are very few enzymes that are physically able to hydrolyze VX.
“I think we have something that is about 100-fold better than the wild-type enzyme. So, this has come a long way for us and is where we are heading next,” said Raushel.
- Tsai, P.-C., N. Fox, A.N. Bigley, S.P. Harvey, D.P. Barondeau, and F.M. Raushel. 2012. Enzymes for the homeland defense: Optimizing phosphotriesterase for the hydrolysis of organophosphate nerve agents. Biochemistry (July).