BTI researchers are working to discover, understand, and improve our ability to enlist the help of molecules that catalyze life.
by Mary Hoff
Enzymes are the movers and shakers of the biomolecular world. A class of proteins found in every cell of every living thing, they bring together molecules that would otherwise be reluctant to interact so they can combine, exchange parts, or otherwise alter each other.
In nature, enzymes facilitate thousands of processes from photosynthesis to decomposition. Enzymes speed up chemical reactions thousands of times faster than the reactions would occur on their own. Over the millennia, humans have found ways apply this superpower to accomplish a variety of useful goals from making beer and cheese, to making our laundry whiter and brighter, to cranking out millions of copies of a sample of DNA to solve crimes or find long-lost relatives.
“And that’s just the beginning,” says Romas Kazlauskas, professor in the department of Biochemistry, Molecular Biology, and Biophysics. “Enzymes can also learn how to do different things. We’re trying to figure out which parts are important and why they’re important, then design something different to do a reaction that doesn’t occur naturally.” By identifying enzymes, improving understanding of how they work, and applying them to new tasks, Kazlauskas and BTI colleagues are taking advantage of the billions of years of evolution that produced these molecules to make medicines, degrade pollutants, speed industrial processes, and more.
Trash to Treasure Kazlauskas is working with an enzyme found in nature that degrades PET plastic. First synthesized in the 1940s, PET (a form of polyethylene) is widely used for beverage and food containers with some 70 million tons generated every year—and much of that ending up in landfills and the ocean. Current efforts to recycle the material can only produce lower-quality plastics.
“One idea is to break down to component parts and resynthesize fresh plastic that would be just as good as what you started with,” he says.
Sound like a job for an enzyme? Kazlauskas thought so, too. But the likelihood of finding a suitable one in nature was slim because PET didn’t exist for most of evolutionary history. Nevertheless, in a compost heap in Japan, researchers recently found an enzyme that bacteria use to break down the waxy part of plants that could also break down PET.
Kazlauskas, along with graduate student Colin Pierce and colleagues, is working on modifying that enzyme known as cutinase, to improve its ability to degrade PET. The goal, ultimately, is to be able to develop a commercially viable way to turn old PET into new plastics without experiencing the loss of quality. This would not only reduce the load of plastic waste, it would also reduce pressure to produce more plastic, often from fossil fuels.
Kazlauskas sees huge opportunities beyond PET for efforts to extend nature’s ability to degrade compounds. “There are a lot of cases where we start making stuff and putting it out in nature, and people say it doesn’t degrade,” he says. “We’re finding bugs that can degrade these forever chemicals.” he says. By advancing the ability to modify such natural enzymes to make them do the job even better, the hope is to avoid the buildup of undesirable, manufactured compounds in the environment and reduce the need to make more from raw materials.
Life on the Edge
Turning somersaults in a sulfurous hot spring or clinging tenaciously to life on a glacier, the organisms studied by McKnight Presidential Fellow Trinity Hamilton, associate professor in the department of Plant and Microbial Biology, are the stars in microscopic world’s version of “Survivor.” Having evolved within living things, most enzymes work best under fairly mild conditions with respect to things like temperature and acidity. But not all. In the hot springs of Yellowstone National Park, Hamilton is studying how microbes—and the enzymes they use to carry out the activities of daily life—can survive regular temperature fluctuations of 40 degrees Celsius (104 degrees Fahrenheit) or more. And, on the other end of the spectrum, she’s also looking at how other microorganisms that live on ice maintain their function at low temperatures in the absence of liquid water.
Hamilton studies, among other things, enzymes that facilitate photosynthesis and function well up to 72 degrees Celsius, and then suddenly quit. “We have no idea why,” she says. “It’s really hard to perform autopsies on microbes.”
The ability of bacterial enzymes to function at various temperatures is behind the process that makes it possible to sequence DNA using what is called the polymerase chain reaction (PCR) technique. The enzyme used for this was isolated from bacteria in a hot spring in Yellowstone National Park. A better understanding of how bacteria keep these proteins active under extreme conditions could open the door to advancing our ability to solve other human challenges like preserving food or thriving in the face of climate change.
Molecular Assembly Line
For Michael Smanski, a McKnight land grant professor in the department of Biochemistry, Molecular Biology, and Biophysics, the focus is on bringing together enzymes from different sources to create an efficient work team that can produce a specific molecule.
Most recently he’s been focusing on serofendic acid, a molecule found in the blood of fetal calves. In the early 2000s, researchers in Japan discovered that serofendic acid could prevent the untimely death of neurons and potentially serve as a therapy for minimizing damage from Parkinson’s disease, strokes, and other neurological trauma. The problem? It occurs in such small quantities that it would take 1,000 calves to make a minute 3 milligrams of active substance—providing dismal prospects for practical use.
Biosynthesis and enzymes to the rescue. Using databases describing enzymes from different organisms and the type of work each does, Smanski and colleagues designed a molecular assembly line that could make serofendic acid from readily available feedstock chemicals. Then they introduced the corresponding genes into a bacterium, enabling it to make the desired product.
As any industrial engineer would know, populating an assembly line with ready workers is only part of the solution, however. For efficiency’s sake, it’s also important to have the right capacity at every step of an assembly process to ensure that partially made products don’t pile up, or a slow step doesn’t drag down everything else. To optimize production of serofendic acid, Smanski has been tweaking the activity levels of the various enzymes relative to each other.
Even as he’s working on a strategy to improve outcomes for individuals with brain disorders, Smanski is also discovering principles that can be applied more broadly to optimizing artificial biosynthetic processes.
Optimizing a process means testing multiple levels of expression for the specific gene that’s coding for each enzyme along the way. If the assembly line consists of 15 enzymes, and researchers want to test five levels of expression for each, that would require 5 15 power—more than 30 billion—individual trials. Using combinatorial mathematics, Smanski is devising a strategy for selecting from those millions of possibilities, a mere 100 or so that are most likely to succeed, making the optimization process far more manageable.
“As improvements in the technical aspects of genetic engineering make it easier to rewrite the genetic blueprints of living organisms, learning how to efficiently sift through all of the possibilities of what-to-write is becoming more important,” Smanski says. “We think that our work at the interface of combinatorial mathematics and genetic engineering will benefit any application that requires more than one or a few genes working together.”
Bringing multiple enzymes together in an assembly line is far more easily said than done. The molecules involved in sequential steps must be physically located close enough to each other to be able to pass a product-in-the-making down the line. They also must be positioned correctly at their stations so they can accomplish their task.
Distinguished McKnight University Professor Claudia Schmidt-Dannert is on it. Rather than identifying enzymes to string together to accomplish a molecule-making task, she is working on the assembly line itself.
Her goal is to not only design a stable assembly line of enzymes able to make a useful product but to genetically modify a microorganism—say, the bacterium E. coli—so that it can produce it on its own. Such a self-assembling scaffold, she believes, could dramatically improve the function of molecular assembly lines, reducing the cost of producing pharmaceuticals and other useful products.
“If we stabilize enzymes, we can make reactions more efficient,” she says.
Schmidt-Dannert and colleagues recently received a patent for a self-assembling, modular scaffold that co-locates enzymes in a way that enhances their ability to efficiently produce desired molecules. Her current focus is on developing scaffolds as materials that can correctly self-assemble into 3-dimensional architectures to organize and support enzyme functions. This would allow the manufacture of a broad range of chemicals including pharmaceutically active molecules—a process that can be extremely difficult using conventional chemical synthesis methods.
She’s also applying her strategy to making molecular assembly lines more economical by including enzymes that recycle required co-factors, which are molecules or metals that assist enzymes in assembling a molecular product.
“You need to recycle the [co-factors]. Otherwise, the process is too expensive,” she says. “A scaffold helps make that possible.”