Heterologous Production of the C33-C45 Polyketide Fragment of Anticancer Apratoxins in a Cyanobacterial Host.

A polyketide synthase subcluster of cytotoxic apratoxin A was isolated from a environmental DNA library and engineered with a thioesterase II domain for heterologous expression in the filamentous cyanobacterium sp. PCC7120. Further engineering with a rhamnose-inducible promoter led to the production of (2,3,5,7)-3,7-dihydroxy-2,5,8,8-tetramethylnonanoic acid, a stereogenically rich chiral building block that is important to the efficient synthesis of apratoxin analogues, representing the first synthetic biology attempt for this type of polyketide fragment.