Studies on Calicheamicin Biosynthesis and Self Resistance

Natural products (NPs) and NP derivatives are an unrivaled, but highly under-represented, resource. Arugably among the most notable natural products discovered to date, the 10-membered enediynes - exemplified by the saccharide-fused calicheamicins (CLM) and the anthraquinone-fused dynemicins (DYN) - offer unprecedented molecular architecture, spectacular biological activity and demonstrated clinical utility. The objective of the first phase of this study (CA84374, years 1-4) was to i) clone and characterize the CLM gene cluster from M. echinospora, ii) develop the genetic tools to address CLM biosynthesis in M. echinospora, iii) investigate the mechanism(s) of CLM self-resistance, and iv) initiate aryltetrasaccharide biosynthetic studies. With these goals largely achieved and new tools/information in place, the second phase of this program (CA84374, years 5-9) was focused upon i) cloning and characterization of the DYN gene cluster from M. chersina, ii) development of genetic tools to address DYN biosynthesis in M. chersina, iii) initiating enediyne core biosynthetic studies, iv) structurally characterization of the CLM self-sacrifice resistance protein CalC, and v) the elucidation of key aryltetrasaccharide biosynthetic transformations (sugar N-oxidation, thiosugar formation and GT-catalyzed aryltetrasaccharide assembly). The successful completion of the majority of phase II aims enables the proposed course of study for this competitive renewal. Specifically, we will focus upon i) extending our understanding of enediyne core biosynthesis, ii) delineating the potential role of CalC in regulating CLM production in M. echinospora, iii) completing the study of key aryltetrasaccharide sugar nucleotide transformations (sulfur installation and sequential C-C alkylation of the N-alkyl dideoxypentose), iv) initiating an enediyne structural biology program and v) synthesizing and evaluating (neo)glycorandomized libraries of CLM and DYN.