Biosynthetic assembly of cytochalasin backbone

Cytochalasins are an important class of fungal natural products in view of structural diversity and biological activities. Although their biosynthetic studies have been examined extensively, the detailed molecular assembly mechanism remains to be solved. We have succeeded to heterologously express the cytochalasin polyketide synthase–non-ribosomal peptide synthetase (PKS–NRPS) hybrid gene ccsA and the trans-acting enoyl-CoA reductase gene ccsC in Aspergillus oryzae. The resultant transformant produced a novel metabolite possessing the cytochalasin backbone. This established that CcsA is capable of constructing the octaketide connected with phenylalanine in collaboration with CcsC, and that CcsA R domain catalyzes reductive cleavage of the thio-tethered PKS–NRPS product.