When awarded the 2018 Chemistry Nobel Prize, Professor Frances Arnold became the 52nd female laureate out of the so far 908. Originally trained in mechanical and aerospace engineering, it was not written in the stars that she would make a deep impact on the field of chemistry. Today, thousands of labs around the globe practise Directed Evolution, a method pioneered by Frances Arnold for design of enzymes able to perform given tasks in industry or academic research.
Just like a catalyst at a chemical production facility, enzymes enable or accelerate biological reactions without being consumed in the process. The suite of enzymes found in nature today has been underway for millions of years, and the process is still ongoing. Evolution.
“I see evolution as a remarkable algorithm, which continuously produces diversity. Tiny alterations – mutations – in the DNA sequence will spur different properties and still more complexity. What we do is to use the same process to re-engineer enzymes found in nature and improve their value in the service of humankind,” says Frances Arnold.
New substances in the chemical toolbox
As an example, Frances Arnold and her co-workers are able to perform new chemistry by creating carbon-silicon bonds in bacteria. While both carbon and silicon are highly abundant elements on Earth, they do not bond in biological systems.
Initially, the team identified the protein family of cytochromes c as promising. Cytochromes contain heme, which is a coordination complex consisting of an iron ion and a porphyrin ligand. For instance, heme is known from the protein hemoglobin, responsible for oxygen transport in blood. Cytochromes c are electron transport proteins, and generally do not have catalytic functions. But they do have a small amount of activity for forming carbon-silicon bonds.
Further, Frances Arnold’s team chose a cytochrome c found in bacteria in hot Icelandic springs. This was practical, since this protein is highly stable, for instance being able to survive boiling – so 100 degrees C.
Using the wild type protein as starting point, the researchers would run consecutive iterations, each time making tiny changes to the DNA sequence. The resulting products were screened for improved functionality. A negative answer would dismiss the product, while a positive answer would trigger further iterations.
In this way, Arnold and co-workers have created a new enzyme able to catalyse carbon-silicon bond formation with more than a thousand turnovers – which is much better than the best small-molecule catalyst invented by chemists for this type of carbene-insertion reaction. Further, the team managed to produce the enzyme in bacteria with high yields.
Recently, the group was able to transfer the same principle to carbon-boron bonds, also not seen in the biological world. In other words, Frances Arnold has added two new elements to the toolbox of biological chemistry. As often the case for fundamental research, the applications for biological carbon-silicon and carbon-boron bonding chemistry remain to be found. However, given the track record of the Nobel laureate, this should only be a matter of time. Frances Arnold is co-inventor on over 50 US patents.
“As an engineer, I have always felt that inventions are not really useful, until they are converted into products which people can actually hold in their hands.”
Startups inspire to new research
An example of such a new product is insect pheromones for crop protection. Application of the pheromone will disturb insect reproduction – with high specificity, so only the harmful insect species is affected – and thus replace farmer’s use of pesticides. While this principle has been known for quite some time, it is only now through application of new enzymes and new chemistry that pheromones can be produced in the relevant quantities at competitive costs. The pheromones are produced by the start-up company Provivi, co-founded by Frances Arnold in 2013 with two former students.
In all, Frances Arnold has co-founded four companies, and she does not see any conflict between fundamental and applied science.
“As I see things, my science is applied. Typically, you will have a technology and a vague idea on how it can be applied. Only as you actually start a company and begin to explore these opportunities will you learn the true potential. Often, the final application will be far from what you had imagined. So, my advice for keen entrepreneurs is that being flexible and able to pivot is important. You need to be willing to change direction rapidly, and most importantly involve people with other competencies than the scientific.”
This is quite natural, Arnold feels:
“You cannot expect people in a science lab to be specialists in business development also. But the really interesting part is that if you keep an open mind, you will learn a lot from the challenges faced by the start-ups you are involved with. This is inspiration to take back and incorporate in your science.”
In the case of pheromones for crop protection, this biotechnology has a direct positive environmental impact by replacing pesticides. Even more importantly, production based on enzymes will contribute in more subtle ways to general improvements in industrial sustainability. Enzymes produced through directed evolution can be applied in production of everything from biofuels to pharmaceuticals, and in more sustainable manner in comparison with traditional methods. By operating at lower temperatures and generally milder conditions, enzymes can replace harsh and energy-consuming chemistry. Further, enzyme catalysis is often able to replace traditional catalysis involving precious metals which are scarce and expensive. And finally, enzymes have high specificity meaning that the amounts of waste are minimized.
"I see evolution as a remarkable algorithm, which continuously produces diversity"
NOBEL LAUREATE FRANCES H. ARNOLD , PROFESSOR AT CALIFORNIA INSTITUTE OF TECHNOLOGY
“Waste minimization and a higher purity of the end products are currently the main drivers for application of enzymes in industry. This is seen especially for high-value products such as pharmaceuticals,” notes Frances Arnold, regretting that the argument of climate change mitigation does not carry the same weight.
“Over the past ten years, we have seen a lot of scientific progress in enzymes that enable production of biofuels. But as long as society does not put a price on carbon emissions, it is hard to produce biofuels at a price able to compete with pumping oil out of the ground.”
Speaking of carbon emissions, it is tempting to ask whether Frances Arnold sees difficulties in finding funding for biofuel research in a time, where USA has recently pulled out from the Paris Agreement?
“Fortunately, we are still able to attract funding for promising projects. Regardless of the political developments, public agencies continue to do good work. Also, many forward-looking companies engage still more in the search for more sustainable production. President Trump says what he says, but industry is smart, realizing we need to become sustainable.”