Collaborative Research: Structural, Functional and Evolutionary Basis for the Utilization of a Quinone Methide-Like Mechanism in the Biosynthesis of Plant Specialized Metabolites

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

Plants synthesize a vast array of compounds that facilitate interactions with their environment, from attracting pollinators and seed dispersers to protecting themselves from pathogens, parasites and herbivores. Each plant species has evolved the ability to synthesize a unique set of such chemicals, often classified as secondary or specialized metabolites. While large numbers of such compounds have been identified, our understanding of the enzymes responsible for their biosynthesis is lagging far behind. Of particular interest is a group of metabolites called the phenylpropenes, consisting of a complex set of bioactive volatile chemicals including eugenol and isoeugenol, that have played important roles in human history and continue to serve important agricultural and dietary needs of humankind. The biosynthesis of the phenylpropenes, which are found only in plants, occurs through an unusual reduction reaction. The research groups led by the PI and CoPI have recently identified two representative enzymes responsible for phenylpropene biosynthesis, eugenol and isoeugenol synthases (EGS and IGS), that catalyze the formation of eugenol and isoeuegnol, respectively, from biosynthetic precursors of the plant polymer lignin. The goals of this project are to study the reaction mechanism of the EGS-IGS type enzymes, to identify related enzymes that synthesize other agriculturally and nutritionally important phenylpropenes, and to use this knowledge to modify such enzymes by rational design to create more efficient biosynthetic pathways for economically reliable sources of existing and new high-value phenylpropenes. It is hypothesized that these enzymes use a 2-step mechanism involving a quinone methide-like intermediate that has not previously been studied in detail and that may also be involved in the syntheses of other important, non-phenylpropene specialized compounds. The investigators use a multidisciplinary approach that includes biochemical, genomic and metabolomic approaches to identify new genes and enzymes for phenylpropene biosynthesis, crystallographic studies to solve the 3-dimensional structure of the proteins, and chemical synthesis of substrates and substrate analogs combined with experimentally modified enzymes to examine reaction mechanism. The project also integrates the training of high school students, teachers, undergraduate students and PhD level scientists in state-of-the-art multidisciplinary research. The research will lead to the identification of a number of new enzymes capable of synthesizing phenylpropenes with important agricultural and nutritional properties, and result in a better understanding of how these enzymes work. It will therefore also lead to the rational engineering of new enzymes that can synthesize novel phenylpropenes with enhanced bioactivity as well as the ability to biosynthesize existing compounds more efficiently. Furthermore, since other enzymes that are involved in the synthesis of distinct plant compounds may utilize a similar mechanism, the biochemical research will increase our understanding of the function of these important enzymes as well. The project will also contribute to the multidisciplinary training of the next generation of scientists--including women and minorities--at all levels, as post-docs preparing to assume faculty positions, as graduate students, and as undergraduates preparing to choose a specific career in science. Furthermore, an outreach program to high-school teachers and students will positively influence high school students considering a career in science in the first place. To disseminate the knowledge gained in this project, the research results will be presented at scientific meetings and published in refereed scientific journals, and in addition, the researchers will give occasional talks to the general public about their work and its implications as well as contribute materials to the general public's media such as print, radio and TV as they have done in the past.