Ectopic expression of the minimal whiE polyketide synthase generates a library of aromatic polyketides of diverse sizes and shapes

The single recombinant expressing the Streptomyces coelicolor minimal whiE (spore pigment) polyketide synthase (PKS) is uniquely capable of generating a large array of well more than 30 polyketides, many of which, so far, are novel to this recombinant. The characterized polyketides represent a diver se set of molecules that differ in size (chain length) and shape (cyclizati on pattern). This combinatorial biosynthetic library is, by far, the larges t and most complex of its kind described to date and indicates that the min imal whiE PKS does not independently control polyketide chain length nor di ctate the first cyclization event. Rather, the minimal PKS enzyme complex m ust rely on the stabilizing effects of additional subunits (i.e., the cycla se whiE-ORFVI) to ensure that the chain reaches the full 24 carbons and cyc lizes correctly. This dramatic loss of control implies that the growing pol yketide chain does not remain enzyme bound, resulting in the spontaneous cy clization of the methyl terminus. Among the six characterized dodecaketides , four different first-ring cyclization regiochemistries are represented, i ncluding C7/C12, C8/C13, C10/C15, and C13/C15. The dodecaketide TW93h posse sses a unique 2,4-dioxaadamantane ring system and represents a new structur al class of polyketides with no related structures isolated from natural or engineered organisms, thus supporting the claim that engineered biosynthes is is capable of producing novel chemotypes.