Discovery and Characterization of SAM-Dependent Pericyclases

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Nature uses enzymes to accelerate chemistry with high efficiency and selectivity. Enzymes are employed in making complex materials known as natural products. Many of these reactions are of importance to the chemical community, and having stable enzymes to carry them out can lead to greener chemistry. Gaining new understandings of how these enzymes function is therefore important towards applications in the chemical industry, as well as discovering new enzymes that are stable and powerful. This award from the Chemistry of Life Processes Program in the Chemistry Division examines the underlying properties of a new class of enzymes discovered recently in the laboratories of Professors Yi Tang and Kendall Houk at the University of California at Los Angeles: a set of enzymes that catalyze pericyclic reactions. Pericyclic reactions are immensely important in synthetic chemistry, as they can lead to the formation of multiple bonds in a single step. However, only a few examples of such enzymes exist and the chemistry is very limited compared to what can be done using organic compounds. This set of pericyclases uses a partner, S-adenosylmethionine or SAM, to catalyze a set of transformations never before seen in biology. This propject combines a multidisciplinary team to study these enzymes using biochemical, structural and computation methods. Results from this work can illuminate the underlying basis of catalysis, and enables us to search through other microbes for additional examples. The project also integrates an outreach program that involves local high school students and undergraduate students in our research laboratories to perform mentored research, and introduces them to the power of enzymes. Pericyclic reactions are among the most powerful synthetic transformations to make multiple bonds regioselectively and stereoselectively. These reactions have been widely applied for the synthesis of biologically active complex natural products containing contiguous stereogenic carbon centers. Despite the prominence of pericyclic reactions in total synthesis, however, only limited enzyme catalyzed pericyclic reactions have been characterized over the past five decades. LepI represents a new family of pericyclases (enzymes that catalyze a pericyclic reaction) that use S-adenosylmethionine (SAM) to catalyze biologically unprecedented reactions, including hetero-Diels Alder cyclization and a [3,3]-sigmatropic retro-Claisen rearrangement. The overarching goal of this project is to understand the structural and mechanistic basis of the reactions catalyzed by pericyclases in the LepI family, especially the role of SAM in catalysis and how periselectivity (selective formation of one pericyclic reaction product) is controlled. A combination of biochemical, structural and computational characterization methods are being used to study the enzyme. The proposed studies are leading to new insights into how nature catalyzes these challenging reactions and controls the regio- and stereoselectivity, and will establish a new role for SAM in enzyme catalysis.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.