CRYSTAL STRUCTURES OF POLYKETIDE SYNTHASES: STRUCTURE-BASED DESIGN OF NOVEL POLY

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Polyketides are a structurally diverse class of natural products that have pharmacologically important activities such as anti-cancer, antibiotic, cholesterol lowering and immunosuppressive properties. (20% of the top selling drugs in the world are polyketides.) They are synthesized in nature from a limited repertoire of simple carboxylic acids by multifunctional proteins called polyketide synthases (PKSs). Determination of crystal structures of PKSs will greatly facilitate the pharmaceutical utilization of PKSs by protein engineering or substrate engineering to produce the next generation of "unnatural" polyketide antibiotics. Previously, we solved the crystal structures of two thioesterases from erythromycin polyketide synthase (DEBS) and picromycin polyketide synthase, respectively, and the crystal structure of priming ketosynthase (ZhuH) from R1128 polyketide synthase utilizing the beamtime at SSRL. This represents a promising start toward the eventual goal of elucidating the high-resolution structure of a complete polyketide synthase. Within the past 6 months we have developed several important constructs for ketosynthase (KS) and acyl transferase (AT) domains from DEBS. More recently, we have crystallized both native and inhibitor bound KS-AT didomain proteins from module 3 and module 5 of DEBS. Preliminary data has shown that these crystals diffract in the range of 3-5 ¿¿ Currently we are preparing additional crystals of these didomains as well as crystals of other didomain proteins. Beamtime at SSRL is urgently needed to solve the crystal structures of these prototypical proteins from modular PKSs for which no known structure is currently available.