Evolution-Oriented Modular Excision of Polyketide Synthases at a Splice Site of Enoylreductase Domain Yielded an...

Polyketide natural products represent a major source of medicinal compounds. The majority of them are biosynthesized by the modular polyketide synthase (PKS) assembly line in Streptomyces spp. Due to the high sequence similarity among the coding regions of PKSs, recombination-mediated gene truncation is prevalent in PKSs. These recombination sites can be the guidelines of reprogramming PKSs for designed biosynthesis. Herein, we have discovered that a PKS module excision naturally occurred between two adjacent enoylreductase (ER) domains in the PKS assembly line of carboxyl polyether ionomycin (INO). The recombination led to significant accumulation of a two-carbon truncated product of INO, neoionomycin A, which exhibited significant anti-inflammatory activities in both zebrafish neuroinflammation and mouse colitis models. Moreover, the natural fusion site of the ER domain was successfully applied to generate the second PKS module excision, yielding another truncated product of INO. The study should represent the first instance of generating the functional hybrid PKS module via a splice junction within the ER domain, thereby adding a new reference site for the rational PKS reconstruction.