Enzyme Evolution and Emergence of Novel Catalytic Functions

Enzyme evolution underlies major expansions of metabolic complexity with profound biological implications. In this talk, I will discuss emergence of cyclization reactions catalyzed by terpene synthases. Cyclic terpenes mediate numerous biological functions in modern plants and provide bioactive compounds for human use, including artemisinin, the most effective treatment for malaria currently available. Guided by the available structural, kinetic, and sequence data, we have constructed mutant libraries which include combinations of amino acids responsible for inducing cyclization reactions in an enzyme that produces E beta-farnesene, a linear hydrocarbon chain. We have used measurements of kinetic rates and mass spectrometry in order to assess catalytic efficiency and specificity of the mutant enzymes. Inspired by spin glass models adapted from statistical physics, we have developed a model which predicts properties as a function of enzyme sequence. Using this model we have inferred evolutionary patterns of enzyme energetics. We have also developed a bio-physical model on fitness of an enzyme based on its catalytic properties. Our studies provide quantitative insights into evolutionary dynamics of a major enzyme family, and highlights the importance of epistasis.