In the Tsai lab we study how enzymes in nature create bioactive molecules called polyketides, which are used to treat many diseases. We use a variety of techniques such as x-ray crystallography, molecular biology, microbiology, organic synthesis, and computational biology in order to uncover the mysteries of natural product biosynthesis. Our lab also is interested in determining the structures of protein complexes involved in fatty acid biosynthesis.
Polyketides are a diverse class of natural products produced by fungi and bacteria that possess a large assortment of biological activities and are used to treat many diseases. Examples of polyketides in pharmaceuticals and health care include tetracycline (antibiotic), lovastatin (cholesterol-lowering), epothilone B (chemotherapeutic) and rapamycin (immunosuppressant). Polyketides are biosynthesized either by multi-domain enzyme complexes called the polyketide synthase (Type I PKS) or by a series of individual enzymes (Type 2 PKS). The Tsai group is interested in understanding the mechanism by which these bioactive molecules are biosynthesized. We utilize X-ray crystallography and structural analysis in parallel with biosynthesis, chemical biology, and computational biology to aid in our understanding of PKS enzyme machinery with the end goal of engineering new bioactive molecules.
Synthesis of Polyketide Analogues
Polyketide intermediates are very reactive and cannot be isolated. As a result, they are very difficult to study. This has hampered efforts to understand the reactions
and enzymes involved in many important steps of polyketide biosynthesis. Our lab uses atom replacement strategies to synthesize small molecule mimics of biosynthetic intermediates in order to better understand how enzymes handle highly reactive polyketides. The molecules we design also are used to aid in protein crystallization and induce complex formation of enzymes.
Fatty Acid Biosynthesis
Fatty acids in E. coli are made by a set of enzymes called a type II fatty acid synthase. Growing fatty acids are shuttled by the acyl carrier protein (AcpP) and delivered to the active sites of target enzyme for elongation and modification. AcpP forms very transient interactions with partner enzymes, and structure elucidation of these complexes is a significant challenge. We utilize mechanism based crosslinking approaches to trap fatty acid biosynthesis in action and solve complex crystal structures. This pathway is a target for biofuel production, and understanding the protein-protein interactions in this system are critical for metabolic engineering efforts.