Engineering Enzyme Functions at Will
Enzymes are proteins capable of carrying out some kind of reaction, and they are formed by several hundred to several thousand of just 20 types of amino acids linked by peptide bonds. Rather than having a flexible, string-like structure, enzymes are precisely folded into highly complex three-dimensional structures. They work to facilitate reactions by taking substrates into their internal chiral space and lowering the activation energy through various means. Nature holds enzymes with wonderful, yet-undiscovered functions. I am engaged in research to discover novel enzymes and to rationally modify and improve their functions, and I would like to introduce a few examples of this work.
[Improving Enzyme Function through Rational Design]
In recent years, the three-dimensional structures of many enzymes have been determined, and their detailed reaction mechanisms have been elucidated. With this information, it has become possible to rationally design enzyme functions and modify them at specific, targeted points. Although we are still in a trial-and-error phase, I believe that if the precision of the design improves, it will be possible to create enzymes with desired performance in a much shorter time and at a lower cost compared to conventional random mutagenesis.
Parameters such as an enzyme's substrate specificity and maximum velocity are fixed, and it has long been considered extremely difficult to alter them easily. Among these challenges, improving enzyme activity through mutagenesis was the most difficult task, and few researchers attempted it. Recently, by applying rational design to an arylmalonate decarboxylase (AMDase) that we originally discovered, we have succeeded in creating mutant enzymes with activities not found in nature, such as an S-selective AMDase with inverted stereoselectivity and a racemase that acts on unnatural compounds. Furthermore, by redesigning the active site through the introduction of mutations at a few specific amino acid sites, we have successfully increased the activity by tens to ten thousand times. A 10,000-fold increase in enzyme activity means that the cost of an enzyme in a certain manufacturing process could be reduced from one million yen to 100 yen, which has an extremely large industrial impact. In this way, we were able to demonstrate that enzyme activity can be improved through rational design.
[Discovery of a PET-Degrading Enzyme]
PET resin, a polyester of terephthalic acid and ethylene glycol, is widely used for containers such as bottles and for fibers in clothing. However, it was long believed that no microorganisms existed that could readily degrade the highly stable PET resin. Recently, our group, in collaboration with a group from the Kyoto Institute of Technology, succeeded in discovering the world's only microorganism capable of degrading PET resin and in analyzing its genome. It seems this microorganism had gone undiscovered because it grows very slowly and degrades PET inconspicuously. We also discovered a novel PET-degrading enzyme (named PETase) that is expected to have applications in the surface processing of PET fibers and in PET recycling. We have already filed a patent application and aim to improve its performance for practical application.
[Conclusion]
Enzymes have superior functions as catalysts and enable the construction of green processes, so it is necessary to further expand their range of applications in the future. Together with energetic and talented students, I will continue to search for and create unique enzymes with features that will astonish the world. By significantly improving their properties, I hope to contribute to the realization of ultra-high-efficiency processes.