Engineering Enzymes for New Stereoselective and Stereodynamic Processes: An Integrated Chemistry -Bioengineering- X-Ray Crystallography-Molecular Dynamics Approach

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Most pharmaceutical drugs and agrochemicals are what is referred to as fine chemicals. The molecules have very specific structures that give them their beneficial properties. Enzymes are highly effective in producing such structures. The objective of this project is to develop a strategy to design and tune the activity of enzymes that are involved in the production of a class of fine chemicals called taxanes. These compounds have anti-cancer properties. One of the taxanes, taxol, is currently used in the treatment of metastatic breast cancers. The project will include educating and mentoring undergraduate and graduate students at the interface of biomolecular engineering, chemistry and structural biology. A collaboration with the science department at a large public high school with a diverse student population is also planned. These efforts will develop a workforce to support a vibrant bioeconomy.The tools of molecular dynamics simulation and x-ray crystallography will guide the directed evolution of two promising nicotinamide-dependent oxidoreductases. The focus is on engineering these enzymes for reactions in which racemic substrates can be effectively deracemized and converted to primarily one of four possible stereoisomers through dynamic reductive kinetic resolution. The targeted transformations will provide access to a spectrum of valuable building blocks for natural products synthesis, chemical biology and medicinal chemistry. Several building blocks to be constructed are for chemotherapeutic agents of the taxane family, useful as anti-cancer drugs. In previous work, the team has shown that the Clostridial enzyme (CaADH) shows remarkable substrate promiscuity, while at the same time exhibits considerable stereochemical fidelity. Preliminary results suggest that the origins of this behavior lie in a flexible binding pocket. A key goal of this project is to understand how this flexible active site is able to adapt to substrates of different shapes and functionalities and stereoselectively transform these substrates. More specifically, the team seeks to elucidate the mechanisms by which such biocatalysts effectively make two ‘stereochemical choices’, namely enantiodiscrimination (choosing one of two rapidly equilibrating enantiomers-sets first stereocenter) and facial discrimination (delivering a nicotinamide-derived hydride equivalent to one of two diastereofaces-sets second stereocenter).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.